Greenhouse Technology 596 by 8bjVAt


									                       Greenhouse Technology
                                    Booklet No. 596
                  Agricultural Engineering and Technology: AETS - 3
I.     Introduction
II.    Size of the Greenhouse
III.   Structural Details
IV.    Siting and Erecting of a Greenhouse
V.     Plants for a Greenhouse
VI.    General Care of Plants in Greenhouse
VII.   Maintaining the Greenhouse Structure
VIII. Plant Troubles


       Greenhouse growing is not merely a money making proposition nor is it a simple
pastime calling for occasional action. It is instead an absorbing hobby, which enables to
produce a range of plants which can be used for commercial purposes also. If used properly
greenhouse offers a way to extend the joy of gardening.

Dr. K.T. Chandy, Agricultural & Environmental Education

I. Introduction

       A greenhouse helps in extending the gardening activities and allows us to grow plants
that might otherwise be impossible. Inside greenhouse we have a protected environment and a
group of plants which rely on us for their very existence, As a definition, we can state that «A
greenhouse is generally a place where plants are raised and cultivated rather than set out for
display". A greenhouse offers a way to extend the joy of gardening, so it should be used
properly. Outdoor, plants are in a environment where one can not control -frost, wind, rain and
other environmental hazards. Here the results depends entirely on the type and facilities inside
a greenhouse and our own skill rather than on the various of soil type and

        Greenhouses need constant attention at most times of the year and this means every
day in summer unless we install an automatic ventilator and an automatic watering system. It
should not be considered merely as a money making proposition nor it is a simple pastime
calling for occasional action. Instead of absorbing hobby which enables one to produce a range
of plants at a time when the garden counterparts are far C behind or their growth outdoor is
impossible. Judicious use of greenhouses helps in attaining good profits when used
commercially. Here in a greenhouse there is: a steady stream of jobs to do, but none of those is
strenuous which makes green- house growing especially suitable for the not so-young and the

A greenhouse can be used for:
-Producing half hardy perennials or bedding annually grown from seed both during sowing and
pricking out.
-Protect tender plants and bulbs during the winter months.
-Grow hobby plants such as chrysanthemums, fuschia's or exotic orchids.
-Cultivate indoor pot plants.
-Cultivate alpine species.
-Use it for commercial purposes.

        The site for a greenhouse should be preferably close to main electricity and water
supplies. The site should be level, open and should not be sheltered and overshadowed by
trees. Ideally oriented so the long axis can lien east-west to optimize the use of light.

II. Size of the Greenhouse

   It can be of any convenient size ranging from 6 ft x 4.5 ft to 20 ft to 10ft. Recommending the
most suitable size is not an easy task and one has to consider various factors. A tiny house
saves money but has two disadvantages.
   1. It is much more difficult to control the environment in a small house than in a large one,
       draughts and sudden fluctuations in temperature are serious problems.
   2. Most gardeners find that they need more space after a year or two; If space is available
       it is advisable to buy a modular greenhouse which can be extended if needed.

   The most popular size of a greenhouse is 8 feet long x 6 ft wide, where space is restricted. If
we want to have staging on both sides of the house, then 10 ft x 8 ft size is advisable. The size
should be in keeping with the area of the garden; a large green house can be very costly to heat
and a structure which is more than 8 ft well usually need a concrete base.

Ill. Structural Details

        This comprises of the following details.
A. Frame
        Aluminium alloy has taken over as the most popular material for greenhouse frames for
several reasons. It is cheaper than wood and requires no painting or other treatment and the
thin glazing bars mean more light within the house. There are certain drawbacks like aluminium
greenhouses lose slightly more heat at night than wooden ones and condensation drips are
more likely to occur. If aluminium frame is poorly designed it may twist in windy or hot weather
and panes may be broken. Now pre-drilled holes are there on main frame so fixing shelves/
hooks is not a problem.

        Wood is considered by many to be most attractive material. The main problem is that
rot-proof timber is so expensive, teak and oak are very costly and the cheaper western red
cedar is still appreciably more expensive than aluminium. These rot proof frames should be
rubbed with linseed oil every few years to enhance their appearance. Fittings should always be
of brass or galvanized iron. If one opts for a soft- wood greenhouse then make sure that the
wood has been pressure treated with a preservative. Plant safe preservatives should be used
for painting treatment every few years.

        Unplasticised rigid polyvenyl chloride (PVC) is the latest material, which is generally
quite expensive but requires little maintenance and also is decay proof. It requires only
occasional washing to remove dust/ bird droppings. Its main drawback is that, it is not a strong
material, which means that glazing bars have to be as thick as wooden ones and with large
buildings the UPVC frame requires a metal core.

       Galvanized steel is still used in the manufacture of commercial greenhouses but is no
longer popular for home models. The great advantage of this material is its rigidity and strength,
which means it can support a large roof. This is of little advantage for an ordinary 8 ft x 6 ft
house, and the fact that the galvanized or painted surface can become scratched and then
pitted with rust is a disadvantage.

B. Floor
        The traditional pattern for the floor of the greenhouse was to have one or both sides as
border soil for growing plants and a central pathway made of concrete, concrete slabs or
wooden slabs, but most experts no longer rec9mmend using border soil for growing annual
plants such as tomatoes. The problem is a build-up of diseases, pests and other troubles in the
soil. Growing in bags and pots are preferred these days. The floor of the greenhouse is entirely
functional, where carpeting is not practical; stone or reconstituted stone slabs are quite popular.
Terracotta tiles are a good choice.

C. Guttering
       Guttering is useful as rainwater dripping from the roof can undermine the foundations.
Some models have built in guttering as a standard fitting. The water from the gutter should be
channelled into a soakway or into a plastic water butt.

D. Door
       Hinged or sliding both types have their disciples. Sliding doors don't slam shut and they
can be used as extra ventilators in an emergency. But they do get stuck occasionally and the
nylon bearings may need replacing. Hinged door generally fit better.

E. Lighting
        Lighting is not essential, but horticultural lamps can increase the range of activities under
glass. An electric point will be acquired within the house.

F. Ventilators
        There are times when a series of rapid air change become necessary within the
greenhouse. Unfortunately the ventilators fitted on most standard models, are inadequate.
There should be at least one roof ventilator (ridge vent) and one side ventilator (side vent). The
roof ventilators are all important. The total ventilator area along the ridge should be 16-20 per
cent of the total floor area. These hinged ventilators should open to at least 55°. Side ventilators
need not open so widely and louvered ones are generally better than the traditional hinged type.

         An automatic ventilator like extra hinged ones may be described as an optional extra.
But it is useful equipment for those who cannot spare the time to go out daily to open and close
the ventilators by hand. An extractor fan is sometimes fitted close to the ridge at the end
opposite to the door which helps in producing enough air movement in the greenhouse.

G. Watering equipments
          A greenhouse is a rainless place where water requirements are to be fulfilled only by the
owners of the green house. Watering by hand is time consuming and is probably the most
difficult to master. The first requirement to make things easier is a tap within the greenhouse. To
make things even easier one can use trickle irrigation system. Watering can, hose pipe and
even use of sand bench capillary matting can be other alternatives.

H. Blinds
       Plants must be protected from the suns rays in summer as overheating can be a serious
problem. For this purpose blinds are generally regarded as the best answer. One can choose
from a wide selection of roller types made of wooden slates or plastic coated sheetings. When
fitted from outside, the temperature inside the house is reduced and the harmful glare of the sun
is eliminated.

I. Staging and shelving
        For growing pot plants in greenhouses, benches or staging are essential. The two terms
are interchangeable in popular use, but strictly speaking staging is a permanent structure
whereas the bench can be folded up and removed. In the most traditional form slated wooden
staging about 2.5 ft above the ground can be used. Netted staging also are used but both have
the disadvantage of making a poor work surface. Solid staging with a shallow lip is useful as it
conserves heat in winter, holds compost when transplanting or filling pots and can be filled with
water holding material for automatic watering. Shelving is a miniature form of bench which is
secured at head height to hold small pot or trays when space or sunlight is restricted. Now-a-
days metal benches and shelves as optional extras could be purchased. Similarly collapsible
benches enable to grow bedding plants and bulbs at a convenient height in spring and then can
be dismantled in summer to grow crops in growing bags.

J. Insulation
       The general principle is to put an inner lining of transparent plastic close to the glass
even a simple arrangement will cut fuel bills by 20-25 per cent. Tailor made panels are offered
by some greenhouse manufacturers, but the usual practice is to attach polythene sheeting to
the sides of the green- house with drawing pins, staples or adhesive tapes. Not all experts are
enthusiastic about this technique. Another method which gives maximum heat retention and
minimum condensation is bubble polythene which has air trapped within it.

K. Propagator
       Cuttings need a moist and reasonably warm atmosphere in order to root satisfactorily.
Seeds of some important plants, including cucumber and tomato require a temperature of 60-75
degree F in order to germinate properly. A heated propagator is useful for this purpose. A
propagator is a plastic or aluminium container with a glass or transparent plastic cover.
Propagators heated by electricity are better than the one by paraffin, and it should have a
thermostatic control and one or more ventilators at the top of the cover.

L. Thermometer
        A maximum/ minimum thermometer is vital. It can be suspended close to the plants, but
free circulation of air-should be ensured around the thermometer. It should be close to eye level
at the north side of the house.

M. Glazing material
         Until recently, glass was the only glazing material, and it still remains the most popular
choice. Poly carbonate is now becoming the rising star in the glass substitute world. Then, the 2
and 2.5 rnrn sheet of acrylic has been found to have light transmission properties which are
almost equal to glass. It is not quite as strong as polycarbonate and is less-expensive.
Polythene sheeting is the most popular and inexpensive form but main fault as a glazing
material is that it can be torn by strong winds and has poor heat retention properties. Flouro-
plastic film is the best of the flexible sheeting materials as its light transmission equals glass and
its heat transmission is reasonable.

N. Heating equipment
        The unheated or cold greenhouse is generally a place for tomatoes and cucumbers in
summer, chrysanthemums in autumn and alpines bulbs and hardy house plants such as cacti in
winter. If we want to extend this range of plants we do need some form of heater to maintain a
minimum temperature of 7o C during the depths of winter. This is the cool green house and is
the one which the experts recommend for the ordinary gardner. A wide choice of fuels is
available for heating purposes, nowadays the popular choices are paraffin, natural gas, bottled
gas and electricity. Heat source can be a electric fan heater, electric tubular heater, electric
convector heater, paraffin heater, gas heater, piped hot water, linked central heating and
electric heating cable and each one is useful for a particular size/ type of greenhouse, and also
have certain positive and negative points.

IV. Siting and Erecting of a Greenhouse

         The greenhouse should be set well away from trees. Recommended minimum distance
from nearby tree is 30 feet. A wind break such as a hedge is useful on the north and east sides,
as strong winds can damage the structure and even ordinary winds will increase the heating bill.
The green house should be sited at least 15 ft away from the hedge. Glass green house should
not be set close to the road to a play areas. Other sites to be avoided are waterlogged soils and
frost pockets and also recently dug soils. A free standing greenhouse should be located at such
a place that electric wiring is possible, and other requirement are also possibly fulfilled. The best
site for a lean to type of greenhouse is a west facing wall. A firm and level site is essential and if
the structure is larger than 8 ft x 6 ft then a concrete foundation is must.

V. Plants for a Greenhouse

        It is difficult to define just what we mean by a green- house plant. There are some plants
which live their whole lives within the confines of a greenhouse examples include citrus, jasmine
and passion flower, certain varieties of tomatoes cucumbers, short rooted types of carrots,
winter and spring varieties of lettuce and certain other vegetables. Then there are others which
produce their ornamental display and their crops under glass, but have to start their lines
outside the greenhouse or must spend part of their adult life in the open, example are pots of
strawberries which are brought into cool green house from garden in January, late flowering
chrysanthmums which are brought into the greenhouse in late in late September. The final
group of plants have a life pattern which is just the opposite. They produce the ornamental
display or their crops m the garden. For them the greenhouse is a place which provides a
protected environment. This is either of the start of their life as seedlings or cuttings or when
they are established plants in pots and in need of frost-free conditions. Here one can find
seedlings of half hardy vegetables, and bedding plants, cuttings of chrysanthemums and pots
of bedding geraniums and fuchsias waiting for the return of frost free night in the spring.

       According to the plants grown, greenhouses can be a ornamental greenhouse where
there will be no tomatoes or other vegetables and fruits and will be having only flowers as
impatiens plumbago, iresine, hypoestis, streptocarpus, begonias etc. Then there can be
productive greenhouse where vegetables are grown in pots and growing bags. The third and
most popular type of greenhouse is the mixed greenhouse. Here, there are both ornamentals
and fruits growing together. Grape wines reach up to the ridge and the benches hold
pelargonium, Fuchsia and so on in full flowers.

VI. General Care of Plants in Greenhouse

         Growing plants under glass is more time consuming and more challenging than growing
the same numbers of plants outdoors. Out of doors the plants rely to a large extent on the
natural elements for their needs water, warmth, humidity and so on. Water, warmth and
ventilation and so many other requirements of the plants are to be taken care of. For the
beginners there are few golden rules. Firstly, the plant should be chosen which are right for the
conditions. Secondly, all the important jobs should be done before, they become critical, like
insulation before the first frost arrives, pest management before it becomes out of hand,
watering before the leaves droop, shading before the plants get scorched and so on. Next
important point is to look and be with the plants to check, feel of the soil, picking off dead
flowers, looking under leaves for disease symptoms. An equally important is to maintain
hygiene, i.e. to regularly get rid of prunings, dead fruit etc. It also means cleaning of used pots,
trays, sprayers, and tools. For following purposes, special care is required in a green- house.

A. Damping down
       The traditional method is to use a hose pipe for wetting the floor and benches in
summer. As the water evaporates, temperature of the house is lowered and water loss through
leaves is also reduced, resulting in lower requirement for frequent watering. Professional
growers use electrically driven humidifiers to provide a continuous source of water vapour.

B. Heating
        With most greenhouse the comfort level temperature for active healthy growth of plants
is 55-75 degree F (12-25 degree C), but this general statement needs to be qualified.
Germinating seeds generally need higher temperatures than seedlings and mature plants. If
different types of plants are grown, which have different temperature requirements than it is
advisable to divide a section of the house with transparent material and then install an adequate
heater in the warm section. It is necessary to award as much heat loss as possible during the
winter months. Glass should be kept clean to ensure maximum entry to sun rays. About 80 per
cent of the heat is lost through the glass so sides and roof may be lined with polythene sheeting.
In spring and summer the problem is reversed. Dry heat is more dangerous than moist heat. As
soon as the temperature continually remain above 75 degree F (25 degree C) it is essential to
apply some type of shading.

C. Shading
        In summer, the greenhouse can become a dead trap for plants. Many plants types are
damaged when the temperature stays over 85 degree -90 degree F (30 -34 degree C). Other
types of plants such as Begonia, African violet and gloxinia are scorched by summer sunshine.
As stated earlier the best answer is a set of outside blinds which can be raised or lowered
depending on the weather. Internal blinds screen stop the entry of harmful rays of the sun, but
do not reduce the internal temperature. Most people need a simpler form of shading. Small
plants can be placed in the shade of larger ones. Newspaper can be placed over seedlings,
rooted cuttings and plants with delicate leaves. Sometimes people use lime wash as a shading
paint, this is not recommended as it is difficult to take off when not required.

D. Watering
       Among the basic things to remember about watering plants in greenhouse is that roots
need air as well as water. It means the compost should be moist but not saturated. The simplest
way is to look at the surface of pots daily in summers and weekly in winters. In summer plants
may need watering twice a day, in winter they may require water only once a week. Plants need
much more water on a sunny day than on a cloudy day and one should avoid watering where
sun is shining brightly. There may be some watering troubles also specially in case of pots as
mentioned here.

1. Water not absorbed.
Cause: Surface caking
Effect: too much water accumulated in the pot
Symptoms: leaves limp, soft rotten areas, poor growth flowers mouldy, both young and old
leaves fall at the same time and roots brown and mushy and mature leaves turn curled yellow
and wilted, leaf tips brown.
Cure: Prick out the surface with a fork or miniature towel. Then immerse the pot to compost
level in a bucket or bath of water.

2. Water runs straight through the pot
Cause: Shrinkage of compost away from the side of the pot
Effect: too little water available to the plant.
Symptoms: leaves limp and wilted, little or no growth oldest leaves fall first lower leaves curled
yellow and wilted, leaf edges brown and dry and flowers fall or quickly fade.
Cure: Immerse the pot to compost level in a bucket or bath of water.

E. Ventilating
        The need for at least one roof ventilator and one side ventilator in even a small
greenhouse is must. In a well stocked house ventilation is required almost all year around. In
winter the roof ventilator should be: opened an inch or two for a few hours around midday if the
weather is dry and above the minimum temperature of the house. The winter ventilation is vital if
we are using a paraffin gas or oil heater. As spring arrives roof ventilator should be opened
more widely and for longer time in the day but the side ventilators are still kept close. In May the
situation changes the main purpose of the ventilator is to keep the temperature below 250
centigrade. Side ventilators are now kept open. In high summer, besides ventilation shading
also is required.

F. Supporting ,
        Many of the most attractive specimens are either climbers or tall plants with weak stems.
For this purpose giving support becomes essential. Such arrangements should be strong
enough to support the plant in full fruit. Supports which are attached to the greenhouse may be
either horizontal or vertical depending on the requirement. Sometimes such support systems
are needed which are not attached to the structure of the house. Basic examples are wooden
stake or bamboo cane. Instead of one cane 3 or 4 canes should be used around the plant to
support it tall plants. Growing bags are a special case for which self supporting metal frames
which stand around or over one bag are made available.

G. Pots and potting
        Earlier there were just two basic ways of growing plants under glass. Some flowers or
small shrubs were kept in pots but most flowering perennials, shrubs, vegetables and fruits were
grown in border soil. The basic rules were followed. The stake or support in the ground was
inserted prior to and not after planting. One can grow more plants in pots but now there is a
trend to change over to modem technique of growing bag cultivation. They are consistent and
sterile and are capable of giving high yields. These compost filled plastic bolsters are excellent
for vigorous plants like tomatoes, cucumbers and melons, but they need special care as the
rules for watering and feeding are quite different from the way one cares for plants in border

j. Containers can be of following types.
a. Clay pot, advantages: less likely to topple over, porous less likely to water log, traditional
natural appearance.
b. Plastic pot; advantages: less likely to break if dropped watering is needed less often,
decorative forms available.
c. Tub: these are large decorative container in wood, plastic or fibreglass for a shrub or a
collection of smaller plants. Fill bottom with gravel before adding compost and water with care if
drainage holes are absent.
d. Polythene sleeve pot: these are inexpensive and easily stored.
e. Peat pot: useful for potting on before transfer to garden, pot is biodegradable can be planted
directly into soil or compost and no root disturbance.
f. Peat pellet: useful for seed sowing and potting on can be planted directly into soil compost;
should be soaked in water before use.
g. Peat block: these are compressed cube of soil based or soil less compost; it needs careful
handling and is no longer popular.
h. Growing bags: these are plastic bags filled with soil-less compost, drainage holes or silts are
made in the sides and panels are removed from the top to create planting pockets.
i. Raised beds: these are useful where base is paved or soil is badly drained.

H. Growing media
       It can be of any of the following types mentioned here.
1. Garden soil
       Soil taken straight from the garden is not suitable for filling pots. It may contain the pests
and weeds. A 4:1 garden soil/peat mixture can be used for a raised bed which should be
changed after few years.

2. Soil based compost
Here sterilized loam and peat are blended with fertilizers time and sand.

3. Soilless compost
        Because loam is difficult to obtain and its quality is variable, most modem composts are
based on peat or peat and sand. These have several advantages over soil based ones.

VII. Maintaining the Greenhouse Structure

        This is done for keeping the plants in peak condition and to inhibit pests and diseases.
The routine should be to carry out an annual overhaul in autumn and to take an immediate
action at any time of the year if there is an emergency.
This includes the following schedule.

A. Autumn cleaning indoors
       For this, the plants should be removed, then rubbish, old pots etc. to be removed and
then a stiff brush, scrapper, sponge and a dilute warm water solution of disinfectant is
recommended. Cracks, crevices, T-section bars in aluminium houses should be specially
cleaned. Disinfectant should be spread and left for working for hours and then should be hosed
down with help of long handled brush and plain water.

B. Autumn cleaning outdoors
        Glass and framework can be cleaned using water and detergent or a dilute solution of a
horticultural detergent with help of a long handled mop to reach the roof sections. Walls and
base if present should be cleaned by scrubbing the bricks and block walls with water and
specific cleaner. For wooden sides, algae and moss should be removed with a proprietary moss
C. General maintenance
        This includes more than just cleaning the glass, frame work shelves, staging etc. All iron
and steel fittings, hinges and screws should be checked for rust and treatment. Replacements
should be done as per the need. Draughts are a special problem so checking of vents and
doors should be done. One can fit self-adhesive draught proofing strips, if they are not present.
The wooden framework of the house should be inspected and the gutters need cleaning and
repairing if necessary.

       Looking after glass, wood, door, guttering are the other important activities which should
be performed regularly as they otherwise lead to big unmanageable type of difficulties.

D. Feeding
       Plants require ford to remain healthy. A number of elements are involved, the main ones
being nitrogen, phosphates and potash. Commercial peat based composts contain all the
essential nutrients and these last for 6-8 weeks after planting. Feeding Should then start, but
how much and how often will depend on a number of factors.

        Slow growing and dormant plants need little or no food as actively growing ones need
feeding regularly. Liquid fertilizers are the best form for pot and growing bag plants. Solid feeds
should be confined to the borders. Make sure that the compost is moist when feeding plants as
applying fertilizer to dry compost can lead to injury. Foliar feeding is an interesting technique
here, dilute fertilizer is applied directly on the leaves. Too little or too much fertilizer, both lead to
specific types of problems, so fertilizer application should be done timely, judiciously and

E. Lighting
        Most greenhouse gardeners rely solely on natural light. It is lack of light as well as low
temperature which cause plant growth to slow down in winter. This is not just a matter f of dull
days. Day length is also important. Most plants need illumination for 12-16 hours per day in
order to maintain active growth. Installing light has several advantages in winter. The increase in
the duration and intensity of light boosts seedling and young plant growth and also induces
flowering in some types. The most important advantage is however that one can work in the
greenhouse during long winter evenings. Here two warnings are necessary. One has to be sure
that the lamps chosen are the one recommended for horticultural use, and the other point, that
some plants require a period of short days and so may be harmed by artificially extending the
day length in winter.

VIII. Plant Troubles

       The warm and moist conditions within a greenhouse provide a paradise for many pests
and diseases. Few natural enemies are present and the breeding rate of organisms can be
amazingly high. There are times when one has to spray or ignite a smoke but a great deal can
be done to prevent problems if rules of good hygiene are followed strictly.

        For this the first and foremost point is to prevent trouble before it starts as never bring
trouble into the house i.e. never use un-sterilized soil, or unsterilized manures. Inspect new
plants carefully and take any remedial action which may be necessary before putting them with
their plants. The house should be kept clean; for this a garden disinfectant can be used. Good
growing practices should be followed by ensuring proper ventilation. Dry air encourages pests
such as red spider mite and thrips saturated air encourages diseases. Watering should be done
in morning so that leaves can dry before nightfall. Dirty rainwater should not be used for

        Border soil should be sterilized annually to prevent the build up of harmful organisms.
Plants should be fed regularly for which potash is important. Plants should also be inspected
regularly, by paying special attention to underside of the leaves.

         If there are problems, than the golden rule is to tackle the trouble without delay. For this,
first do not spray insecticide as minor attacks by caterpillar and leaf minor can be controlled by
hand picking. Mouldy leaves and fruits should be removed. Then one should go for the right
treatment if needed. Spraying, fumigating or dusting may be necessary. Pesticides are safe to
use in the way described on the label with all precautions. For this first we should make sure
that product is recommended for use under glass and for the plant in question. Other important
point is that treatment should always be done in right way, like do not spray or fumigate when
the sun is shining close all ventilators before using a smoke take care with aerosols, spraying
too closely will cause scorch, do not spray open delicate blooms, spray them roughly both
above and below the leaves. Finally, always follow .the after treatment rules.


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