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					                                                                                                                                   Gardening in the
                                                                                                                                   Global Greenhouse
                                                                                                                                   The Impacts of Climate Change
                                                                                                                                   on Gardens in the UK




     Gardening in the Global Greenhouse was funded by the following organisations:




     Research was carried out by:




The UK Climate Impacts Programme
The UK Climate Impacts Programme (UKCIP) is based at the University of Oxford and funded by DEFRA to coordinate an assessment of
how climate change will affect the UK, and help organisations assess how they might be affected.
UKCIP, Union House, 12–16 St. Michael’s Street, Oxford, OX1 2DU, UK; enquiries@ukcip.org.uk.
Tel: +44(0)1865 432076; Fax: +44(0)1865 432077.
Summary report written by Dr Phil Gates, University of Durham.
Cover images (from top): Protea longiflora (NT); Hardy’s Cottage (Eric Chrichton, NTPL); Nymans (Patsy Fagan, NTPL).
Printed on 50% recycled paper.
Published in November 2002 under the UK Climate Impacts Programme.                                                                 Summary Report
Gardening in the Global Greenhouse: Summary Report                                                                                                 Introduction




Introduction: The British and their gardens

The British are noted for their love of gardens. As an art form, gardening is an essential
part of our culture. It is one of the leading hobbies in Britain, with an estimated 27 million
gardeners (41 per cent of the population) participating in some way. Gardeners sustain
a multi-million pound horticultural retail industry. Our heritage gardens and their plant
collections, representing 500 years of garden history, attract 24 million visitors each year,
contributing an estimated £300 million to the tourism industry.

                                                          A wake up call from the weather

                                                          Gardeners are more aware than many how              organisations, commercial horticulturists,
                                                          the weather affects them and their interests.       landscape consultants, the horticultural press,
                                                          Over the last four decades, extreme weather         and representatives from local and national
                                                          events have severely damaged many gardens           government, universities and research
                                                          and resulted in major economic losses. These        organisations, to consider how gardens would
                                                          events include:                                     be affected by climate change.

                                                          • severe winter weather in 1962/63 that             The primary outcome of the meeting was
                                                            killed many hardy plants;                         the commissioning of a technical report,
                                                                                                              entitled ‘The Impacts of Climate Change
                                                          • drought in 1976, which weakened trees
Drought dried out lakes and reservoirs in 1976                                                                on Gardens in the UK’, by Richard Bisgrove
(Mike Sleigh, RHS)                                          and dried out lakes;
                                                                                                              and Professor Paul Hadley, of the University
                                                          • storms in 1987 and 1990 that felled               of Reading (2002). The authors assembled
                                                            millions of trees;                                and evaluated evidence on how plants and
                                                                                                              garden components respond to altered
                                                          • torrential and prolonged rain leading to
                                                                                                              climatic conditions, and assessed the likely
                                                            soil erosion, flooding and drowning of
                                                                                                              impact of the UKCIP 1 climate change
                                                            plant roots in 2000 and 2001.
                                                                                                              scenarios on gardens in the United Kingdom.
                                                          These events highlight the vulnerability of
                                                                                                              This document summarises their report. It
                                                          gardens to the vagaries of weather and
                                                                                                              describes effects on garden plants, domestic
                                                          climate. A workshop was held in London in
                                                                                                              gardens, nationally important heritage
                                                          April 2000, attended by gardening
                                                                                                              gardens, the landscape industry and the retail
Trees at Chartwell, Kent felled by the storm in 1987                                                          horticultural industry. It discusses aspects of
(Peter Baistow, NTPL)                                                                                         gardening that might benefit from climate
                                                                                                              change and identifies techniques and
                                                                                                              practices that might reduce undesirable effects
                                                                                                              of climate change on gardens. It also
                                                                                                              highlights the important role that gardens can
1
    The UKCIP02 scenarios describe how the climate of                                                         play in raising awareness of environmentally
    the UK is likely to change over the course of the
    21st century. They were produced for the UK Climate
                                                                                                              sustainable practices which can minimise the
    Impacts Programme by the Hadley Centre at the Met.                                                        effects of climate change, and identifies areas
    Office and by the Tyndall Centre for Climate Change
    Research with funding from the Government’s                                                               for further research.
    Department for Environment, Food and Rural Affairs.   Flooding at Westbury Court, Glos. in 2000/01 (NT)




                                                                                                                                                            1
Gardening in the Global Greenhouse: Summary Report                                                                        What is happening to our climate?   Gardening in the Global Greenhouse: Summary Report                                        What is happening to our climate?




What is happening to our climate?

The current phase of climate change is part of a continuous warming of the climate                                                                                            Change in average winter and summer temperature for the low and high emissions scenarios.
recorded over the last 150 years and is being caused primarily by industrial activities
that have raised levels of greenhouse gases which retain heat within the atmosphere.                                                                                            Winter                                           Summer
                                                                                                                                                                                        2020s                 2050s      2080s      2020s    2050s    2080s
                                                                                                                                                                                                                                                                           deg C
There is overwhelming evidence that the rate          In the low emissions scenario, at the current    • mean annual rainfall may decrease by
of warming is increasing, although                    rate of 0.1°- 0.3°C rise per decade annual         10-20 per cent, but with 10-30 per cent                                                                                                                                4.5

projections for the rate and extent of                average temperatures will increase by              more falling in winter and 20-50 per cent                Low                                                                                                           4
                                                                                                                                                                  Emissions
warming vary, depending on predictions of             1° - 2.5°C by the 2080s. This lower rate of        less in summer by the 2080s. Rain will                                                                                                                                 3.5

economic growth, human population levels              increase would depend on the use of clean          tend to fall with greater intensity;                                                                                                                                   3

and compliance with international                     and efficient technologies, reduced use of                                                                                                                                                                                2.5
                                                                                                       • by the 2080s summer droughts will be
agreements to regulate emissions of carbon            natural resources that generate carbon                                                                                                                                                                                    2
                                                                                                         more frequent, as will very wet winters,
dioxide, the most important greenhouse gas.           dioxide, and global solutions to problems
                                                                                                         but autumns will be drier. Higher                                                                                                                                      1.5

                                                      of social and economic stability and
In the UKCIP02 high emissions scenario, with                                                             temperatures and less cloud cover in                     High
                                                                                                                                                                                                                                                                                1

                                                      equity between developed and                                                                                Emissions
rapid economic growth in developed and less                                                              summer will lead to greater evaporative                                                                                                                                0.5

                                                      developing countries.
developed countries and a market driven                                                                  loss from soils and leaves,
reliance on fossil fuels, by the 2080s                Climate change is already occurring and            worsening drought conditions;
average temperatures are likely to rise by            further change is inevitable, with common
                                                                                                       • although predictions for extreme weather
2°- 4.5°C, at a rate of between 0.3°- 0.5°C           consequences for climate in the UK. These are:
                                                                                                         events are less certain than for
per decade. This is between two and three
                                                      • higher mean annual temperatures, which           temperature, weather patterns are likely to
times faster than the current rate of
                                                        will increase the length of the growing          become more erratic, with greater
temperature increase.
                                                        season for many plants. A 1°C increase in        frequency of torrential rain, temperature
                                                        mean temperature will increase the               extremes and storms.
                                                        growing season by three weeks in south
                                                                                                                                                                              Percentage change in average winter and summer precipitation for the 2020s, 2050s and 2080s
                                                                                                       Within these overall trends there will be
                                                        east England and by 10 days in the                                                                                    for the low and high emissions scenarios
                                                                                                       pronounced regional differences, with the
                                                        north west;
                                                                                                       lowest rainfall and highest temperatures
                                                      • greater warming in summer and autumn           occurring in south east England. The reduction                          Winter                                            Summer
                                                        than in winter, with summer maximums           of soil moisture will therefore be greatest in                                 2020s                  2050s       2080s       2020s    2050s    2080s                 per cent

                                                        rising faster than summer minimums,            areas where water supplies are already low.                                                                                                                                    30
                                                        leading to increased frequency of hot
                                                                                                       By the 2050s sea levels are expected to rise                                                                                                                                   25

                                                        summer days. By the 2080s temperatures                                                                                                                                                                                        20
                                                                                                       by 14-18 cm, and by the 2080s by 23-36 cm.
                                                        may exceed 42°C about once per decade                                                                   Low                                                                                                                   15
                                                                                                       The effects will be greatest in the south east,          Emissions
Traditional scenes such as this at Bodnant, Gwynedd     in lowland England;                                                                                                                                                                                                           10

will become a rarity (Christopher Gallagher, NTPL)                                                     where the land mass is naturally subsiding.
                                                                                                                                                                                                                                                                                      0
                                                      • winter minimum temperatures rising faster      Coastal flooding could damage some                                                                                                                                             -10
                                                        than winter maximums, leading to milder        domestic and major heritage gardens.                                                                                                                                           -20

                                                        winters with a reduced temperature range                                                                                                                                                                                      -30
                                                                                                       These climate changes will have major
                                                        and fewer frosts. In many parts of the UK,                                                                                                                                                                                    -40
                                                                                                       effects on plant growth and on the
                                                        especially in the south west, frosts will be                                                            High                                                                                                                  -50
                                                                                                       ways in which we design, plant and                       Emissions
                                                        rare and might occur in Cornwall only
                                                                                                       maintain gardens.                                                                                                                                                  Changes within
                                                        about once every 10 years by the 2080s,                                                                                                                                                                         'natural' variability

                                                        although local variations will occur.
                                                        Snowfall will decrease everywhere in
                                                        lowland and coastal regions by as much as                                                                             Source: UKCIP02 Climate Change Scenarios

                                                        90 per cent by the 2080s, and by 60 per
                                                        cent in high snowfall areas such as the
Droughts will become more frequent (NT)                 Scottish Highlands;

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Gardening in the Global Greenhouse: Summary Report                                                                            Plants in a warmer world   Gardening in the Global Greenhouse: Summary Report                                                                                 Plants in a warmer world




Plants in a warmer world: how climate affects plant growth and development

Plants are influenced by extreme weather events and by gradual climate changes, the effects of                                                           “Grape cultivation could extend                                                                    Failure of plants to shut down metabolic
                                                                                                                                                                                                                                                            activity in winter might increase frost damage,
                                                                                                                                                          as far north as Scotland during
which are more insidious but potentially dramatic. A small change in average annual temperature                                                           the second half of the
                                                                                                                                                                                                                                                            but higher sugar levels generated in tissues
                                                                                                                                                                                                                                                            of evergreen species by winter growth might
of, say, 0.1°C has a cumulative effect through the growing season, with a large net impact. An                                                            21st century.“                                                                                    have the reverse effect. Species-specific effects
analogy would be a small change in bank interest rate, which might have little immediate effect                                                            Bisgrove and Hadley (2002)                                                                       are likely, and further research is needed.
on the daily economy but would have a profound impact on annual accounts.                                                                                                                                                                                   Interactions between higher carbon
                                                                                                                                                                                                                                                            dioxide levels and higher temperatures
                                                                                                                                                                                                        Grapes could be grown in Scotland in future (RHS)
                                               Effects of individual elements of climate        so although plants will grow more rapidly,                                                                                                                  As temperatures rise, plants respond more
                                               change have been tested in controlled            fertiliser requirements do not necessarily                                                              flower earlier, but others such as honesty          vigorously to higher carbon dioxide levels.
                                               environments for some plant species of           increase. Increases in carbon dioxide levels                                                            (Lunaria annua) and bleeding heart (Dicentra        Doubling atmospheric carbon dioxide levels
                                               agricultural importance and there is already     can hasten bud burst, flowering and fruiting                                                            formosa) will be largely unaffected.                and raising temperature by 3°C can increase
                                               evidence that rises in temperature and           and lead to earlier cessation of growth,                                                                                                                    growth by over 50 per cent, although this
                                                                                                                                                                                                        Temperature increase is likely to extend the
                                               atmospheric carbon dioxide levels have           depending on species investigated. In roses,                                                                                                                may not be reflected in higher yields. The
                                                                                                                                                                                                        northern limit for growing some vegetables
                                               increased growth of forest trees. Further        higher carbon dioxide levels increase the                                                                                                                   benefits are greater in vegetables harvested
                                                                                                                                                                                                        and fruit. Grape bud burst and maturity
                                               research is required for the majority of         number of flower buds, which bloom earlier                                                                                                                  early in development, such as carrots, than in
                                                                                                                                                                                                        dates may advance by up to 50 days and
                                               garden plants.                                   and accelerate flowering.                                                                                                                                   those that are cropped closer to maturity,
                                                                                                                                                                                                        yield may increase by up to 25 per cent by
                                                                                                                                                                                                                                                            such as onion and cauliflower. Warmer
                                               Higher carbon dioxide levels                                                                                                                             the 2050s.
                                                                                                                                                                                                                                                            temperatures shorten the growing period of
                                               Atmospheric carbon dioxide, the primary                                                                                                                  Temperature levels play a key role in               vegetables like onions, lowering ultimate
                                               agent of climate change, is used by plants in                                                                                                            regulating the annual growth cycle of               yields. In potato, higher carbon dioxide levels
                                               photosynthesis to produce chemical energy,                                                                                                               perennial plants. Normal bud burst often            increase rates of photosynthesis and so
                                               sugars and other organic molecules essential                                                                                                             depends on accumulated experience of                slightly increase overall yields, but higher
                                               for plant growth and development. Increases                                                                                                              winter chilling, which breaks dormancy and          temperatures hasten foliage death.
                                               in carbon dioxide levels, which are expected                                                                                                             prepares buds to open as soon as favourable
                                               to rise from the current 350 parts per million                                                                                                           spring weather arrives. At the end of the
                                               (ppm) to between 525 and 810 ppm by the                                                                                                                  growing season, falling temperatures halt
“.. doubling carbon dioxide                    2080s under the low and high emissions           Higher carbon dioxide levels can hasten bud burst
                                                                                                (Stephen Robson, NTPL)
                                                                                                                                                                                                        growth and trigger leaf fall. The intervening
 levels can increase plant growth              scenarios respectively, will increase the rate                                                                                                           period constitutes the growing season, which
 by as much as 50 per cent ..“                 of photosynthesis and so enhance plant                                                                                                                   will extend as climate changes. Currently
                                               growth. Experiments show that doubling                                                                                                                   spring is arriving 2 - 6 days earlier per
    Bisgrove and Hadley (2002)                                                                  Higher temperatures
                                               carbon dioxide levels can increase plant                                                                                                                 decade and autumn two days later each
                                               growth by as much as 50 per cent, although       Higher temperatures increase growth rates,                                                              decade. Precocious spring flowering, delayed
                                               this varies depending on plant species,          provided that no other factors are limiting. It                                                         leaf fall, extended lawn growth and
                                               temperature, water supply and mineral            is unlikely that the higher temperatures                                                                unseasonal winter flowering are already
                                               nutrient availability.                           expected by the 2080s will physically                                                                   commonplace and will increase in extent and
                                                                                                damage plants in the open ground, except                                                                frequency as climate changes.
                                               The way in which plants use the additional
                                                                                                for brief, exceptional periods, but damage
                                               products of photosynthesis varies between                                                                                                                Earlier springs lengthen the growing season
                                                                                                may occur in glasshouses unless these are
                                               species and is affected by other                                                                                                                         and allow earlier planting dates. Bud burst of
                                                                                                well shaded and ventilated.
                                               environmental factors. Under conditions of                                                                                                               most plants will be advanced, but the likelihood    Autumn is arriving later and later
                                                                                                                                                                                                                                                            (Michael Caldwell, NTPL)
                                               water stress, some plants divert resources       Higher temperatures produce faster seed                                                                 of frost damage to precocious growth will be
                                               into root production, improving water            germination, bud burst, leaf expansion and                                                              no greater than at present, because frosts will
                                               uptake. Plants use water more efficiently        flowering. Advances in flowering date can                                                               become less frequent. Frost damage in autumn
                                               as carbon dioxide levels rise, because a         be predicted for species whose temperature                                                              may become more serious, as higher average
                                               reduction in the numbers and opening of          response characteristics are known. Plants                                                              temperatures delay dormancy and clearer skies
                                               stomatal pores on leaf surfaces slows water      like Mexican orange (Choisya ternata) and                                                               increase the possibility of frost.
                                               loss. Nitrogen is also used more efficiently,    Rhododendron ‘Praecox’ are likely to

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Gardening in the Global Greenhouse: Summary Report                                                                                                          Soils   Gardening in the Global Greenhouse: Summary Report                                                                                    Pandora’s greenhouse




Soils: winter waterlogging, summer drought                                                                                                                          Pandora’s greenhouse: more pests, more diseases, more weeds

The UKCIP02 scenarios point to major changes in soil water content and hence nutrient                                                                               Garden pests, diseases and weeds tend to have short, rapid life cycles and reproduce in large
availability. Managing these changes represents one of the biggest challenges for gardeners                                                                         numbers – ideal credentials for organisms that can benefit from the predicted changes in
in the 21st century.                                                                                                                                                climate. Increased temperatures shorten pest life cycles so that populations increase faster,
                                                                                                                                                                    while longer growing seasons allow additional reproductive cycles at a time of the year when
                                                       Seasonal temperature increases will enhance        Sudden heavy downpours, coupled with soil                 pest levels are already high.
                                                       biological activity of soil micro-organisms,       compaction, poor drainage and landscaping
                                                       leading to more rapid breakdown of soil            with impervious materials, will lead to rapid
                                                       organic matter and faster nutrient release.        surface run-off and localised flooding.                   Pests                                             Beneficial or benign insects will be equally      Warmer temperatures in the UK are also
                                                       Increased availability of soluble soil nutrients   Prolonged waterlogging weakens and kills                                                                    affected by temperature change, so                likely to favour a northwards advance of
                                                                                                                                                                    Pests that undergo many breeding cycles in
                                                       will bring about faster and more vigorous          tree roots and will increase the risk of                                                                    increased natural predation of pests is likely.   native pest species and an influx of pests
                                                                                                                                                                    a growing season, such as thrips, aphids and
                                                       plant growth, but will also increase the loss      damage to property from large moribund                                                                      The nematode currently used as a biological       from continental Europe, either by natural
                                                                                                                                                                    spider mites, will complete their life cycles
                                                       of soil nutrients through leaching. Heavier,       trees growing close to houses. Cedars at the                                                                control for vine weevil could become more         migration or accidental introduction.
                                                                                                                                                                    faster. Milder winters will benefit many insect
                                                       intense rain, especially in winter when there      National Trust garden at Osterley Park in                                                                   widely used in future, as warmer conditions       Termites and a distinct strain of the Asian
                                                                                                                                                                    pests that already overwinter as adults,
                                                       is no vegetation cover, may wash away soil         Middlesex and hedges at Westbury Court in                                                                   will enable it to be effective for a longer       gypsy moth (Lymantria dispar ssp.) have
                                                                                                                                                                    while others that currently overwinter as
                                                       minerals, leading to pollution of streams,         Gloucestershire have already been affected                                                                  season. There is already evidence that            already been recorded in southern Britain.
                                                                                                                                                                    eggs may also adopt this strategy. Earlier
                                                       ponds and lakes.                                   by flooding. This can be avoided by improving                                                               butterflies are emerging earlier and that
                                                                                                                                                                    springs will allow them to disperse onto
The compost heap: addition of organic matter will                                                         drainage, using gullies, soakaways and                                                                      their ranges are extending, but increased
become increasingly important (Stephen Robson, NTPL)   Strategies for conserving soil fertility and                                                                 garden plants sooner, provided that these
                                                                                                          ditches in large gardens but is much more                                                                   activity of bees in mild winters reduces their
                                                       moisture will depend largely on soil                                                                         plant hosts also begin growth earlier. The
                                                                                                          difficult to control in closely spaced, small                                                               chances of survival.
                                                       conditions and local effects of climate                                                                      cabbage aphid (Brevicoryne brassicae)
“Evidence suggests that nitrate                        change. Peak garden demand
                                                                                                          suburban gardens.                                         already benefits from mild winters and for        Many insect pests transmit virus diseases,
 losses from soils may double.                         for water will be greatest in the densely                                                                    every 1°C increase in temperature, aphid          which will become more prevalent as pest
 Maintaining soil fertility, by                        populated south east where it is least                                                                       attacks begin two weeks earlier. An increase      infestations intensify and occur earlier in the
                                                                                                                                                                    in spring temperature of 2°C will allow           year, when plants are more severely
 replacing organic matter, will                        available. Free draining sandy soils will lose
                                                       organic matter faster, further reducing                                                                      cabbage root fly (Delia radicum) to become        vulnerable. Insects that are currently
 be essential.”                                                                                                                                                     active a month earlier than at present.           glasshouse pests, such as western flower
                                                       water-holding capacity during summer
    Bisgrove and Hadley (2002)                                                                                                                                      Faster plant growth reduces leaf nutritive        thrips, may move into the open garden,
                                                       droughts, and will be more prone to water
                                                       erosion in winter. Addition of organic matter                                                                value and can increase pest feeding activity      carrying virus diseases such as tomato
                                                       and mulching will be required. Heavy soils                                                                   by 20-40 per cent.                                spotted wilt virus and Impatiens necrotic
                                                                                                                                                                                                                                                                        Warmer conditions will allow greater use of biological
                                                       should retain sufficient water for plant                                                                                                                       spot viruses, which can infect a range of         control of the vine weevil (Chris Prior, RHS)

                                                       growth in summer but winter waterlogging                                                                                                                       vegetables. There is good reason to suppose
                                                       may kill plants unless grit is incorporated or                                                                                                                 that other pest species currently confined to
                                                                                                          Hedges at Westbury Court, Gloucestershire, have
                                                       raised beds are constructed.                       been affected by flooding (John Millar, NTPL)                                                               the sheltered environment of glasshouses
                                                                                                                                                                                                                      will move into the open garden. This has
“Managing rainwater run-off ..                         Higher summer temperatures will increase
                                                                                                                                                                                                                      already happened with red spider mite.
                                                       water evaporation from leaves and the soil,
 will be of crucial importance.”
                                                       lowering soil moisture content. A 3°C
    Bisgrove and Hadley (2002)                         increase in soil temperature, of the kind that
                                                       might be experienced by the 2080s under
                                                       the high scenario, can increase such water
                                                       loss by 30 per cent and decrease soil
                                                       moisture by 25 per cent. When this effect is
                                                       combined with substantially lower summer
                                                       rainfall, plants will suffer from severe drought
                                                       stress more frequently.




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Gardening in the Global Greenhouse: Summary Report                                                                                  Pandora’s greenhouse   Gardening in the Global Greenhouse: Summary Report                                                                                     Pandora’s greenhouse




                                               Horse chestnut leaf miner (Cameraria                 As with insect pests, climate change can be                                                                    There is great potential for severe fungal        There is evidence that bracken (Pteridium
                                               ohridella) has devastated trees in Spain,            expected to bring an influx of new diseases                                                                    damage to plants that form key structural         aquilinum), which is a serious weed on large
                                               become established in Northern Italy and             from overseas, posing major threats to                                                                         elements in the formal planting of heritage       estates, will benefit significantly from climate
                                               recently appeared in Wimbledon. An influx            garden plants. Soil borne Athelia (Corticium)                                                                  gardens, including yew, box and holly. Box        change, colonising at higher altitudes
                                               of exotic pests into British gardens is a likely     rolfsii, which would be a serious threat to                                                                    blight (Cylindrocladium buxicola) is spread       and penetrating further into lightly
                                               consequence of climate change.                       garden plants, has already been introduced                                                                     by water splash and will be favoured by           shaded woodlands.
                                                                                                    into Britain and could become established                                                                      warmer, wetter conditions. Yew root rot
                                               Larger pests, like roe deer and grey squirrels,                                                                                                                                                                       Fears have been expressed about the
                                                                                                    here if warmer winters enable it to survive.                                                                   (Phytophthora cinnamomi) will become a
                                               will be favoured by warmer winters, which                                                                                                                                                                             possibility of the uncontrolled spread of
                                                                                                    Olive scab (Spilocaea oleagina) has also                                                                       greater problem in wetter, warmer winters
                                               will increase their survival rates. Grey squirrels                                                                                                                                                                    alien plant introductions. Himalayan balsam
                                                                                                    been introduced and is an example of how                                                                       and will spread northwards and eastwards.
                                               have a predilection for beech (Fagus sylvatica),                                                                                                                                                                      (Impatiens glandulifera), Rhododendron
                                                                                                    gardeners may inadvertently introduce new                                                                      Holly leaf blight (Phytophthora ilicis) arrived
                                               which is also very sensitive to drought, and                                                                                                                                                                          ponticum and Japanese knotweed (Fallopia
                                                                                                    diseases as they exploit climate changes to                                                                    from the USA in the 1980s and its recent
                                               the combined effects of climate and squirrels                                                                                                                                                                         japonica) have all escaped from gardens
                                                                                                    grow new plants.                                                                                               spread may be due to warmer, wetter
                                               on this species could be particularly severe.                                                                                                                                                                         and pose threats to natural ecosystems. As
                                                                                                                                                                                                                   winters. It has already caused damage in the
                                                                                                    Quarantine regulations, currently designed to                                                                                                                    the UK climate continues to warm it will be
Carmeraria ohridella is now affecting horse    Diseases                                                                                                    Camellia petal blight will spread from Devon            garden at Nymans in Sussex. Other species
chesnuts in England (J. Metzer, LWF)
                                                                                                    protect plants of major economic importance,           and Cornwall (Chris Prior, RHS)
                                                                                                                                                                                                                                                                     necessary to monitor carefully the potential
                                               Plant diseases often have complex life                                                                                                                              at increasing risk from Phytophthora species
                                                                                                    may need to be revised and extended                                                                                                                              and observed threats from invading exotic
                                               cycles and a range of hosts, so predicting                                                                                                                          include Lawson cypress and alders.
                                                                                                    to garden plants. Camellia petal blight                                                                                                                          plants, but the threat that they represent
                                               consequences of climate change for disease           (Ciborinia camelliae), originated in Japan and                                                                 Weeds                                             should not be overstated.
                                               infestations is difficult. Wetter, warmer            has spread around the world, unimpeded by
                                                                                                                                                                                                                   More favourable conditions for germination
                                               winters will favour the spread of water-             plant health authorities that did not consider
                                                                                                                                                                                                                   and growth will increase the need for
                                               transmitted diseases such as Phytophthora,           it necessary to impose import restrictions.
                                                                                                                                                                                                                   weeding, while slow growth in dry summers
                                               or species with higher temperature                   The disease has become established in
                                                                                                                                                                                                                   may reduce the effectiveness of glyphosate
                                               requirements like red-thread (Laetisaria             Devon and Cornwall, at the northern limit of
                                                                                                                                                                                                                   and hormone-based herbicides, which work
                                               fuciformis) disease of lawns. Drier, warmer          its climatic tolerance, but warmer conditions
                                                                                                                                                                                                                   best on plants that are growing rapidly.
                                               summers will increase the incidence of               in future will favour its spread.
                                                                                                                                                                                                                   Herbicide spraying will need to be
                                               aerially dispersed spores of diseases like
                                                                                                    Oak wilt (Ceratocystis fagacearum), a major                                                                    conducted earlier in the year.
                                               powdery mildew.
                                                                                                    disease in North America, is transmitted by
                                               Continued plant growth during mild winters           an insect that cannot survive under current
                                               will enhance winter survival of diseases and         UK climate conditions. When these change,
                                               lead to their rapid re-establishment in earlier      accidental introduction of this insect could
                                               springs. Rates of disease will depend on             be a serious threat to oaks in Britain.
                                               their tolerance of drier, warmer summers but
                                               in general higher temperatures would be
                                               expected to increase the severity of disease
                                               attacks. Drought also tends to increase
                                               plants’ susceptibility to diseases, as in the
                                               case of sooty bark disease (Cryptostroma
                                               corticale) of sycamore. Warmer winters will
                                               favour bark and wood invading fungi such
                                               as honey fungus (Armillaria spp.) and apple
                                               canker (Nectria galligena).                          Warmer conditions will favour honey fungus             Holly leaf blight is already causing damage in the UK
                                                                                                    (Chris Prior, RHS)                                     (Béatrice Henricot)




8                                                                                                                                                                                                                                                                                                                  9
Gardening in the Global Greenhouse: Summary Report                                                                       Garden management in a warmer world   Gardening in the Global Greenhouse: Summary Report                                                                         Garden management in a warmer world




Garden management in a warmer world

The character of our gardens and the plant collections found in them are influenced by the                                                                     “.. in the contemporary garden,                          Climate change and the character                  The retail horticultural trade can respond to
                                                                                                                                                                                                                        of gardens                                        these changes in gardening fashion, and is
                                                                                                                                                                climate change offers exciting
physical constraints of what may be grown, plant hardiness, temperature and water requirements,                                                                 opportunities ..”                                       The extent to which the overall style and
                                                                                                                                                                                                                                                                          already meeting consumer demand for such
                                                                                                                                                                                                                                                                          exotic species as phormiums, bamboos,
and what is desirable from the perspective of historical precedent, culture or fashion.                                                                           Bisgrove and Hadley (2002)
                                                                                                                                                                                                                        character of gardens is affected by climate
                                                                                                                                                                                                                                                                          cannas, palms, tree ferns and bananas which
                                                                                                                                                                                                                        depends on how much we wish to preserve
                                                                                                                                                                                                                                                                          were, until recently, only grown in large,
                                                                                                                                                                                                                        their character for cultural reasons.
“Tresco has spread to Tunbridge                           The craft and science of horticulture allows      Temperature and water                                                                                                                                         specialist gardens.
                                                          us to grow species that are poorly adapted                                                                                                                    Domestic garden design is subject to the
 Wells and is on its way                                                                                    Maintaining plants is particularly difficult                                                                whims of horticultural fashion, promoted by
                                                                                                                                                                                                                                                                          Heritage gardens
                                                          to the climate in the United Kingdom, such
 to Teesside.”                                            as alpine plants and mediterranean species,
                                                                                                            during periods of higher summer temperatures                                                                magazines and television programmes.              Most plants that are currently cultivated in
                                                                                                            and drought conditions, especially in parts                                                                 Historically important gardens are maintained     heritage gardens are likely to be maintained
  Bisgrove and Hadley (2002)                              and also to manage the garden environment
                                                                                                            of southern England where water resources                                                                   as cultural assets – to perpetuate significant    over this century by the use of suitable soil
                                                          to allow cultivation of highly bred cultivars
                                                                                                            are already limited. Even short periods of                                                                  layouts, period styles, plant collections and     moisture conservation techniques and
                                                          which could not thrive unassisted. Current
                                                                                                            extreme stress can kill many annuals and                                                                    the accumulation of past owners’ influences.      irrigation in summer, but at increasing cost.
                                                          horticultural skills will need to be refined to
                                                                                                            perennials, and may weaken perennials and                                                                   In such gardens, maintaining their character
                                                          ensure the survival of existing garden plants                                                                                                                                                                   Difficult decisions over suitable replacement
                                                                                                            trees, making them vulnerable to stress in                                                                  and current combinations of species will
                                                          and allow the cultivation of new species.                                                                                                                                                                       planting will arise when extreme weather
                                                                                                            subsequent years.                                                                                           require special attention and will become         events, such as storms, lead to loss of
                                                          Hardiness                                                                                            Historic collection of plants, such as this fernery at
                                                                                                            Gardeners in areas with summer water                                                                        increasingly difficult and expensive, if          mature trees. When individual plants are
                                                                                                                                                               Biddulph Grange, will become increasingly difficult
                                                                                                            shortages can plant drought tolerant species,      to maintain (Nick Meers, NTPL)                           not unsustainable.                                unique or of particular historical, botanical
                                                          Some 85 per cent of garden plants originate
                                                                                                            but these will require skilled cultivation.                                                                 Destruction of gardens because of climate         or biological importance, then strenuous and
                                                          from areas with warmer climates than our
                                                                                                            Such species do not tolerate saturated soil                                                                 change in the medium term is only likely          expensive efforts will need to be made to
                                                          own. Higher average winter temperatures
                                                                                                            around their roots and will be vulnerable to                                                                in those few coastal gardens that could           maintain them in the face of climate change,
                                                          will reduce frost damage to marginally
                                                                                                            disease in the warmer, wetter winters that                                                                  be directly affected by sea level rise, or        as will be the case for archaeology
                                                          hardy species, such as Abutilon vitifolium,
                                                                                                            can be expected in the 21st century.                                                                        perhaps in some that are subject to               contained within historic parks or gardens.
                                                          Bottlebrush (Callistemon spp.), Carpentaria
                                                          californica and Jerusalem sage (Phlomis                                                                                                                       prolonged and persistent flooding inland.         Balancing consideration of future climatic
                                                          fruticosa), and will extend their cultivation                                                                                                                 In such cases, documentary recording is           conditions with issues of historical
                                                          northwards. In general, higher average                                                                                                                        probably the only option.                         authenticity will become an increasingly
                                                          winter temperatures should enhance the                                                                                                                                                                          important factor in the maintenance of
                                                                                                                                                                                                                        Domestic and contemporary gardens
                                                          winter survival prospects for the majority                                                                                                                                                                      heritage gardens. Garden conservation
                                                          of species grown in our gardens.                                                                                                                              Climate change could bring about rapid            management plans offer a tool to
                                                                                                                                                                                                                        changes in garden style. Adventurous              plan ahead.
                                                          Frost will remain a risk – albeit a                                                                                                                           gardeners have always tried to explore the
                                                          diminishing one – throughout much of the                                                                                                                      limits for cultivating unusual and demanding
                                                          UK, even in a warmer climate, at least until                                                                                                                  species, so climate change could provide
                                                          the end of the 21st century. By judicious                                                                                                                     new variations on familiar challenges. Their
Climate change is likely to extend the range of species   soil preparation and recognition of local                                                                                                                     success will depend on careful soil
that can be cultivated (Derek Croucher, NPTL)                                                                                                                  The horticultural trade is already meeting consumer
                                                          microclimates within large gardens,                                                                  demand for exotic species (Pardee Tree Nursery)          preparation and plant maintenance during
                                                          gardeners already extend the limits for                                                                                                                       periods of drought or excessive rain.
                                                          cultivation of tender species. This skill will                                                                                                                Currently, between 10,000-15,000 plant
                                                          become even more important with climate                                                                                                                       species and varieties are cultivated in British
                                                          change, to minimise the risk of frost damage                                                                                                                  gardens; climate change is likely to extend
                                                          to precocious buds in spring.                                                                                                                                 the range of species that can be cultivated
                                                                                                                                                                                                                        outdoors throughout the year, especially by
                                                                                                                                                                                                                        gardeners in northern Britain.                    Difficult decisions will have to be made when
                                                                                                                                                                                                                                                                          mature trees in heritage gardens are lost through
                                                                                                                                                                                                                                                                          extreme weather (George Wright, NTPL)




10                                                                                                                                                                                                                                                                                                                            11
Gardening in the Global Greenhouse: Summary Report                                                                                 Rewriting the garden manual   Gardening in the Global Greenhouse: Summary Report                                                                                Rewriting the garden manual




Rewriting the garden manual: climate change and key garden components

All gardeners will need to plan for new planting opportunities, a longer growing season,                                                                                                                                Herbaceous perennials                              preparation and irrigation. Higher temperatures
                                                                                                                                                                                                                                                                           will favour use of a much wider range of
                                                                                                                                                                                                                        These are so diverse in their climate optima
improvements in garden drainage and watering facilities, continuous grass mowing and                                                                                                                                    that it is difficult to generalise on their
                                                                                                                                                                                                                                                                           half-hardy bedding plants that will no longer
                                                                                                                                                                                                                                                                           be subject to frosts. Separate spring, summer
difficult growing conditions under glass.                                                                                                                                                                               performance. Traditional herbaceous border
                                                                                                                                                                                                                                                                           and autumn bedding schemes will be
                                                                                                                                                                                                                        species such as aster (e.g. Aster novi-belgii),
                                                                                                                                                                                                                                                                           desirable when the length of the growing
                                                                                                                                                                                                                        delphinium (Delphinium x cultorum), lupin
                                                                                                                                                                                                                                                                           season increases.
                                                                                                                                                                                                                        (Lupinus x regalis spp.) and phlox (Phlox
                                                                                                                                                                                                                        paniculata), requiring deeply cultivated,
                                                        Some of the challenges gardeners will               Fruit trees and bushes                               The plants grown in traditional cottage gardens will   fertile, moisture retentive soil, will not adapt
                                                                                                                                                                 require more care (Neil Chrichton, NTPL)
                                                        face, and some possible solutions, are                                                                                                                          well to drier summers and will need more
                                                        set out below:                                      Many existing cultivars have a minimum
                                                                                                            winter chilling requirement for bud break                                                                   intensive care, as will old cultivars of iris,
                                                        Trees                                                                                                                                                           which tolerate dry summers but are killed by
                                                                                                            and flowering, which may not be met in
                                                        It should be possible to select tree                future mild winters, so maintaining historically
                                                                                                                                                                 “Whilst the challenge for many                         winter waterlogging. Selecting species and
                                                        provenances that will be better adapted to          important cultivars will become more difficult.       gardeners may be the introduction                     cultivars that are drought resistant and
                                                        future climates than present cultivars by, for                                                            of new and exciting species into                      tolerant of waterlogged soils in winter will
                                                                                                            Breeding new cultivars with a lower chilling                                                                be a challenge for plant breeders and
                                                        example, choosing disease-resistant species.
                                                                                                            requirement, or complete substitution of these
                                                                                                                                                                  their gardens, as the climate
                                                        Many existing long-lived trees will suffer stress                                                                                                               nurseries. More thorough staking of
Careful management will help avoid large scale storm
                                                                                                            crops may be needed. Pears, cherries and              progressively changes a much
damage in woodland (NT)
                                                        from climate change and will require careful                                                                                                                    herbaceous plants will be required, to withstand   Lawns will need year-round maintenance
                                                                                                            peaches, for example, could replace apples            greater challenge to gardeners..                      periods of intensive rainfall in summer.
                                                                                                                                                                                                                                                                           (Mike Sleigh, RHS)
                                                        management programmes to deal with:
                                                                                                            in some locations.                                    will be to create the traditional
                                                        • summer drought, minimised by skilled                                                                                                                          Bulbs
                                                                                                            Shrubs                                                English cottage garden.”                                                                                 Lawns
                                                          soil management;                                                                                                                                              Species propagated from bulbs and
                                                        • waterlogging, avoided by planned                  Most problems that afflict trees will also             Bisgrove and Hadley (2002)                           underground storage organs typically require
                                                                                                                                                                                                                                                                           Fine lawns – the icon of British gardens – are
                                                                                                            apply to shrubs, but to a lesser extent, and                                                                                                                   high-maintenance features particularly suited
                                                          drainage measures;                                                                                                                                            low winter temperatures to stimulate root
                                                                                                            the same management procedures apply.                                                                                                                          to our current climate. Hot summers and
                                                        • damage and loss from high winds,                                                                                                                              development and, in some cases, high
                                                                                                            Shade-adapted shrubs can be damaged by                                                                                                                         wetter winters will increase browning during
                                                          requiring planned long term replacement                                                                                                                       summer temperatures to initiate flower bud
                                                                                                            intense sunlight and weed competition after                                                                                                                    droughts, promote soil compaction during wet
                                                          programmes, planting in suitably sheltered                                                                                                                    development. Requirements of different
                                                                                                            storm damage to the tree canopy, requiring                                                                                                                     weather and increase risk of diseases. A longer
                                                          site, and perhaps judicious crown                                                                                                                             species vary widely, but if warmer winters
                                                                                                            temporary shading during a period                                                                                                                              growing season will demand year-round
               Peaches could replace apples
                                                          reduction of vulnerable trees;                                                                                                                                lead to failure of root initiation, lifting and
               (Neil Campbell-Sharp, NTPL)                                                                  of acclimatisation.                                                                                                                                            mowing and lawn care. More extensive moss
                                                                                                                                                                                                                        refrigeration of bulbs would be needed to
                                                        • large scale storm damage in woodland,                                                                                                                                                                            growth in winter is likely, although summer
                                                                                                            Sub-shrubs                                                                                                  ensure normal development. Higher soil and
                                                          minimised by avoiding uniform                                                                                                                                                                                    drought will minimise its impact on the lawn.
                                                                                                                                                                                                                        air temperatures in spring may alter the
                                                          monocultures and planting a diversity             Higher temperatures and fewer frosts will                                                                                                                      These changes will raise maintenance costs
 Trees that are resistant to storm damage                                                                                                                                                                               balance between flower and foliage
 Source: White (1994)                                     of tree species in new woodlands;                 allow wider use of sub-shrubs such as                                                                                                                          in large gardens, making conversion to more
                                                                                                                                                                                                                        development in species such as hyacinth
                                                                                                            Fuchsia, Indigofera and Penstemon, which                                                                                                                       natural meadow areas an attractive proposition
 Acer pseudoplatanus                  Sycamore          • risk of damage to conifer hedges by fire                                                                                                                      (Hyacinthus orientalis).
                                                                                                            are marginally hardy at present in many                                                                                                                        in less formal areas. The cost of lawn irrigation,
 x Cupressocyparis leylandii          Leyland cypress     in periods of extreme drought, reduced
                                                                                                            locations. In northern locations such species                                                               Warmer summers will benefit summer and             if permitted at all in areas of water shortage,
 Magnolia (tree species)              Magnolia            by limiting access and establishing fire
                                                                                                            will still require careful management, to                                                                   autumn flowering subjects and will permit          will be an important consideration.
 Ilex aquifolium                      Holly               prevention measures.
                                                                                                            guard against late damage from frosts,               Faster-growing foliage may obscure hyacinth flowers    cultivation of a wider range of species in the
 Metasequoia glyptostroboides         Dawn redwood                                                                                                               (David Sellman, NTPL)
                                                                                                                                                                                                                        open border. Tulips and some crocus cultivars
                                                                                                            which are unlikely to be totally eliminated
 Robinia pseudoacacia                 Black locust                                                                                                                                                                      do not tolerate waterlogging, so will either
                                                                                                            during the next century.
 Sequoiadendron giganteum             Wellingtonia                                                                                                                                                                      require excellent soil drainage regimes, or will
 Taxus baccata                        Yew                                                                                                                                                                               need to be lifted and stored over the winter.
                                                                                                                                                                                                                        Annuals
                                                                                                                                                                                                                        Higher temperatures in spring will accelerate
                                                                                                                                                                                                                        germination, development and flowering of
                                                                                                                                                                                                                        hardy annuals, and lead to their earlier death.
                                                                                                                                                                                                                        This trend might be minimised by better soil
12                                                                                                                                                                                                                                                                                                                       13
Gardening in the Global Greenhouse: Summary Report                                                                                  Rewriting the garden manual   Gardening in the Global Greenhouse: Summary Report                                                                                            The bottom line




                                                                                                                                                                  The bottom line: the commercial impact of climate change on gardens

                                                       In gardens open to the public, managing            Ponds, lakes and water supplies                         Many major gardens depend on revenue from visitors. Garden managers will need to plan for
                                                       visitor access to lawns to minimise soil
                                                                                                          High summer temperatures will lead to                   the financial impacts of climate change. They will need to meet the cost of storm and flood repairs
                                                       compaction will be important. Unpredictable
                                                                                                          increased frequency of algal blooms in
                                                       summer rain and prolonged grass growth
                                                                                                          ponds, promoting stagnant conditions. Water             and rising insurance premiums, and to adapt to the effects of climate change by installing water
                                                       through winter will force greater flexibility in
                                                       mowing regimes to avoid lawn damage,
                                                                                                          features in gardens will need more intensive            storage facilities and flood protection. They will also need to prepare for a longer visitor season
                                                                                                          maintenance, with frequent topping up of
                                                       raising costs when contracted labour
                                                                                                          small ponds in summer. Seasonal fluctuation
                                                                                                                                                                  and greater visitor impact on the garden infrastructure. There is scope to develop environmentally
                                                       is employed.
                                                                                                          of water levels in large lakes and ponds will           sustainable gardening techniques further.
                                                       In the longer term, conversion to lawns            require the use of spillways and sluices in
                                                       constituted from coarser, more drought             winter and improved marginal planting in
                                                       resistant grasses that tend to be less             summer, to minimise the visual impact of                                                                        Visits to heritage gardens                          Gardeners need to be proactive in managing
                                                       tolerant of close mowing may be needed,            falling water levels.                                                                                                                                               gardens in ways that make minimum
                                                                                                                                                                                                                          Climate, or more precisely prevailing
                                                       to reduce costs of irrigation and                                                                                                                                                                                      demands on scarce water resources, and in
                                                                                                          Supply of water for irrigation during summer                                                                    weather, is just one of many factors that will
                                                       sward maintenance.                                                                                                                                                                                                     demonstrating sound environmental
                                                                                                          could be problematic across the UK.                                                                             influence future trends in garden visits.
The cost of lawn irrigation will be a consideration                                                                                                                                                                                                                           practices to their visitors. This is important,
(David Sellman, NTPL)                                  Garden paths and wooden structures                 Rationing for all but essential uses is likely in                                                               Many social, cultural and economic factors
                                                                                                                                                                                                                                                                              both in terms of managing immediate
                                                                                                          critical areas. Water charges may also                                                                          are involved, including population dynamics,
                                                       Paths act as conduits for storm water run-                                                                                                                                                                             problems caused by the current phase of
                                                                                                          increase, encouraging installation of more                                                                      disposable income, competing attractions
                                                       off, and so are prone to rapid erosion. Path                                                                                                                                                                           climate change, and in modifying behaviour
                                                                                                          efficient irrigation systems and the use of                                                                     and access to gardens by public transport.
                                                       design and choice of surfaces can minimise                                                                                                                                                                             and attitudes to prevent further undesirable
                                                                                                          ‘grey’ water from domestic activities. Water                                                                    Improved weather, especially early in the           climate changes in the future. Gardens open
                                                       this hazard. In winter and early spring
                                                                                                          conservation measures, either via soil                                                                          year, may attract more visitors to gardens,         to the public could help demonstrate
                                                       slippery algal growth on paths is likely
                                                                                                          mulching or collecting of rainwater in water                                                                    while prolonged autumns with 10-20 per              sustainable horticulture techniques.
                                                       to increase.
                                                                                                          butts, will become a summer priority and                                                                        cent less rainfall and enhanced autumn
                                                       In addition to unpredictable storm damage,         large gardens may need to construct                                                                                                                                 Garden industries
                                                                                                                                                                                                                          foliage colour are likely to extend the
                                                       cycles of summer drying and intensive and          reservoirs for irrigation purposes.                     Enhanced autumn colour will extend the visitor season
                                                                                                                                                                                                                          visitor season. Exceptionally high summer           Nurseries and garden centres can benefit
                                                                                                                                                                  (Mike Sleigh, RHS)
                                                       prolonged rain will lead to more rapid                                                                                                                             temperatures would be a deterrent, unless           commercially from climate change, but will
                                                                                                          Hot work
                                                       deterioration of wooden structures. More                                                                                                                           gardens incorporate design features such            experience increased operational difficulties.
                                                       robust construction and use of more durable        Extreme summer temperatures represent a                                                                         as shady woodland and lakeside walks to
                                                       timbers from sustainable sources will be           health hazard. Those working on energetic                                                                                                                           Most plants sold at horticultural retail
                                                                                                                                                                                                                          increase visitor comfort.
                                                       required. Shading and better ventilation in        tasks will need to guard against dehydration                                                                                                                        outlets are grown in containers, with roots
Warmer weather will give rise to more algae in ponds   greenhouses will be needed in summer, for          and sunburn and will require better protective                                                                  Gardens will benefit from investment in             confined in small volumes of growing
(NT)
                                                       the benefit of plants and gardeners who            clothing when working with chemicals in                                                                         visitor facilities, such as glasshouses, shelters   medium. Increased labour costs for watering
                                                       work under glass and, as winters become            hot conditions. Coping with effects of climate                                                                  and information centres, if summer weather          will favour the installation of automatic
                                                       warmer and wetter, good ventilation will be        change will entail more work and stress,                                                                        becomes even more unpredictable.                    watering systems. Contingency planning will
                                                       essential to deter fungal diseases.                resulting from increased routine maintenance                                                                                                                        be required to ensure reliable supplies
                                                                                                                                                                                                                          Garden managers need to be aware that
                                                                                                          tasks and the need for greater flexibility in
                                                                                                                                                                  “The gardening community                                                                                    during drought periods.
                                                                                                                                                                                                                          climate change will favour increases in the
                                                                                                          working practices in large gardens.                      has the potential to set an                            number and variety of biting insects that           Increased incidence of stormy weather will
                                                                                                                                                                   example of good practice                               breed in water, which may deter visitors.           require better staking and support of large
                                                                                                                                                                   which will further increase                                                                                container-grown plants, which are
                                                                                                                                                                                                                          The major impact of more garden visitors
                                                                                                                                                                   public appreciation and                                will be increased wear and tear, especially
                                                                                                                                                                                                                                                                              inherently unstable.
                                                                                                                                                                   support for gardens ..”                                after heavy rain, which could be minimised          Working conditions under glass during hot
                                                                                                                                                                    Bisgrove and Hadley (2002)                            by contingency planning for managing                summer weather will deteriorate, although
                                                                                                                                                                                                                          visitor movements. Gardens can draw on              a milder climate in general will make year-
                                                                                                                                                                                                                          experience from the sports turf industry in         round outdoor working more amenable.
                                                       Brown lawns will become a more common sight
                                                       (English Heritage)
                                                                                                                                                                                                                          coping with wear and compaction of lawns.


                                                                                                          Working in extreme heat represents a health hazard
                                                                                                          (RHS)

14                                                                                                                                                                                                                                                                                                                        15
Gardening in the Global Greenhouse: Summary Report                                                                                               The bottom line   Gardening in the Global Greenhouse: Summary Report                                                                                           Next Steps




                                                                                                                                                                   Next steps: research and action                                                                 Key challenges
                                                     It is difficult to plan for devastating extreme           As undesirable effects of climate change            There are serious limitations in our knowledge of the likely impact of climate change           and opportunities
                                                     weather events, such as storms and hail, but              become obvious to gardeners, there will be          on gardens.                                                                                     Domestic gardens
                                                     businesses in areas with increasing risk of               greater demand for solutions to gardening           This study has highlighted challenges and opportunities for the gardening industry              Challenges include:
                                                     flooding may need to improve water run-off                problems. There will be new marketing               to consider, as well as a number of areas for future research and recommendations               • managing drier soils in summer and wetter
                                                     measures, face rising insurance premiums                  opportunities for environmentally benign            for action (see below).                                                                           soils in winter
                                                     and consider relocation. For garden centres               solutions such as composting and organic                                                                                                            • maintaining soil fertility
                                                                                                                                                                   The partners will explore what research and practical action they can take together,
                                                     and nurseries, contingency planning for                   techniques, water storage equipment and                                                                                                             • intensification of pest, disease and
                                                                                                                                                                   as well as using this study to inform their own policy and decision-making.
                                                     extreme weather damage will become                        biological control methods for dealing with                                                                                                           weed problems
                                                     increasingly important. Extreme weather                   pests. Greater interest in irrigation systems       Research:                                       Recommendations:                                • maintaining a smooth, green lawn
                                                     conditions, such as drought and flooding,                 is also likely.                                                                                                                                     • meeting the needs of drought-adapted
Extreme weather conditions are damaging to garden                                                                                                                  The study has identified a need for             • encourage networking between major
sales businesses (Notcutts)                          are also indirectly damaging to garden sales                                                                                                                                                                    perennials and bulbous species that do
                                                                                                               Climate change will lengthen the growing            research to:                                      gardening organisations and institutions
                                                     businesses, since public interest in gardening                                                                                                                                                                  not tolerate waterlogging in winter
                                                                                                               season and extend peak sales periods for                                                              to exchange and coordinate observations,
                                                     rapidly declines during such periods.                                                                         • establish the degree of exposure                                                              • year-round plant growth, requiring
                                                                                                               garden plants and sundries such as garden                                                             ideas and innovations, disseminate
                                                                                                                                                                     of Britain’s gardening heritage to                                                              continuous maintenance
                                                                                                               leisure equipment. Demand for replacement                                                             information and inform policy decisions
                                                                                                                                                                     climate change                                                                                Opportunities include:
                                                      Plants likely to perform better
                                                                                                               plants for those lost through drought or
                                                                                                                                                                                                                   • initiate a Hortus Europaeus, to map the       • increased range of plants suitable for
                                                      in a warmer climate                                      waterlogged soils in winter will increase.          • identify resources and level of investment
                                                      Source: Emmett (pers. comm.)                                                                                                                                   distribution of garden species in Europe,       cultivation in the open garden
                                                                                                                                                                     required to maintain the integrity of those
                                                      Genus                      Species                       There could be opportunities for marketing a                                                          allowing large scale monitoring of effects    • northwards spread of optimum growing
                                                      Agavaceae                  Agave                                                                               gardens of greatest historical significance
                                                                                                               wider range of perennial exotic species and                                                           of climate change on garden plant species       conditions for some plants
                                                                                 Cordyline (Torbay palm)
                                                                                 Yucca                         plants that are currently half-hardy annuals,       • establish the criteria for the                                                                • warmer and drier summers and autumns
                                                      Aizoaceae                  Carpobrotus (Hottentot fig)                                                                                                       • produce a list of indicator plant species
                                                                                                               which will survive in the open garden in              management of significant plant                                                                 for enjoying the garden
                                                                                 Delosperma                                                                                                                          likely to be sensitive to climate change,
                                                                                 Drosanthemum                  milder winters. Faster growth and flowering           collections on a national basis                                                               Heritage gardens and large gardens
                                                                                                                                                                                                                     allowing nationwide monitoring of its
                                                      Aloaceae                   Aloe                          will encourage gardeners to replant bedding                                                                                                         open to the public
                                                                                                                                                                   • develop a greater understanding of how          progress and impacts
                                                      Araceae                    Alocasia                      and containers more frequently.
                                                                                                                                                                     garden plants respond to climate change,                                                      Challenges include:
                                                      Arecaceae                  Chamaerops
                                                                                                                                                                                                                   • implement practical actions to enable         • maintaining historic gardens, their associated
                                                                                 Trachycarpus      Palms       Exploiting opportunities for marketing a              specifically in relation to:
                Many plants, such as cannas, will                                Phoenix                                                                                                                             gardens to adapt to climate change.             archaeology, wildlife interests, and their specimen
                perform better in a warmer climate                                                             wider range of plants requires advanced               – frost sensitivity and hardiness
                                                      Bromeliaceae               Fascicularia                                                                                                                        Forward plan for flooding, drought,
                (Mark Bolton, NTPL)                                              Puya                          planning, since basic research is required to         – winter dormancy                                                                               plants as they adapt to a changing climate
                                                      Cannaceae                  Canna (Indian shot)                                                                                                                 soil changes and structural impacts           • managing the impact of visitors during less
                                                                                                               identify optimum cultivation techniques,              – flowering and autumn colour
                                                      Crassulaceae               Aeonium                                                                                                                             on buildings, features and facilities           predictable summer weather
                                                                                                               especially for perennials, shrubs and trees           – susceptibility to pests and diseases
                                                                                 Crassula
                                                                                 Echeveria                     which will need to tolerate summer drought            – interactions with symbiotic soil fungi                                                      • dealing with storms and flood
                                                                                 Sedum                                                                                                                                                                             • increased maintenance costs, especially for
                                                                                                               and waterlogging in winter. Research will               and beneficial micro-organisms
                                                      Musaceae                   Ensete
                                                                                 Musa (Banana)                 also be required in ‘hardening off’                                                                                                                   fine grass swards
                                                                                                                                                                   • identification and monitoring of
                                                      Myrtaceae                  Callistemon (Bottle brush)    procedures for species that are marginally                                                                                                          Opportunities include:
                                                                                 Metrosideros                                                                        potentially invasive species
                                                                                                               hardy, although this will become less                                                                                                               • potential for a longer visitor season
                                                      Oleaceae                   Olea (Olive)
                                                                                                               problematic by the 2080s.                           • minimise soil nutrient loss and                                                               • developing an educational role, as centres
                                                      Proteaceae                 Banksia
                                                                                 Leucadendron                                                                        reduce the impact of water logging                                                              of excellence in environmentally sustainable
                                                                                 Grevillea                                                                           and drought on plants                                                                           gardening techniques
                                                                                 Protea
                                                      Restionaceae               Elegia                                                                            • develop methods for mowing grass that                                                         Retail horticulture outlets
                                                                                 Restio                                                                                                                                                                            Challenges include:
                                                                                                                                                                     minimise compaction of wet soils
                                                      Zingiberaceae              Hedychium
                                                                                                                                                                                                                                                                   • maintaining container-grown stock during
                                                                                                                                                                   • improve methods for water management                                                            summer drought
                                                                                                                                                                     in the garden and heat management
                                                                                                                                                                                                                                                                   • minimising the impact of extreme weather on
                                                                                                                                                                     in glasshouses                                                                                  business activities
                                                                                                                                                                   • refine models for regional impacts,                                                           • marketing a wider range of plant species
                                                                                                                                                                     allowing more accurate prediction                                                               and varieties
                                                                                                                                                                     of future local climates                                                                      Opportunities include:
                                                                                                                                                                                                                                                                   • extension of peak periods of gardening activity
                                                                                                                                                                   • investigate garden visitor response
                                                                                                                                                                                                                   The season for visiting gardens will lengthen   • marketing water conservation equipment
                                                                                                                                                                     to climate change                             (Chris King, NTPL)

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