Weeds a common sense guide
Weeds annoy us by thriving where they’re not wanted. It may seem that two pop up for every one we pull. But there are many effective ways to tackle weeds without resorting to toxic chemicals. Take a few minutes to learn how to outsmart weeds the safe way, without herbicides. You’ll be helping to protect the health of our soil, water, wildlife, pets, and families. Mulch, mulch, mulch Mulch is any protective substance that covers the soil. Mulches smother weed seeds by limiting light. Place mulch between plants and over unused plots. Mulch four inches deep in garden beds. Use two inches around shallow rooted plants such as rhododendrons and azaleas. To further cut off weeds, use a base layer under a covering mulch. • Base layers include cardboard and newspaper (thick and well overlapped) and landscape fabric. Take care using landscape fabric because many kinds do not break down, and become tangled with roots. Perennials such as thistles may still pop up through these layers, so also plan to hand weed. • Mulches include sawdust (alder works well), wood chips, shredded bark, shredded yard prunings, pine needles, and old cedar shavings (which are naturally weed-repellent). Watch where you water Install soaker hoses or drip irrigation, so you water plants, not paths or weeds! Bury soaker hoses three inches deep in soil or mulch to reach plant roots.
Step 1: Prevention – The Best Management
Use plants to fight weeds
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• Plant fast-growing annuals in new shrub beds to temporarily fill in the space between slow-growing shrubs. Examples: sweet alyssum (Lobularia maritima), farewell to spring (Clarkia amoena), and scarlet flax (Linum grandiflorum). • Space plants closely to crowd out weeds. • In vegetable gardens, plant a cover crop such as crimson clover or winter rye in the fall. In early spring, dig the plants into the soil. Limit sources of weeds • Keep weed seeds out of your garden by choosing seeds, soil, and mulch from reliable sources. If you use manure, make sure it has been “hot composted” to kill weed seeds. • Before introducing a plant to your garden, ask if it is a type that spreads and takes over. Inspect nursery plants to make sure they don’t contain weeds. • Learn your plants’ fertilizer needs. Overfertilizing encourages weeds. • Limit how much you work the soil. Every time soil is turned over, weed seeds are brought near the surface where they can sprout. If you do turn your vegetable garden, apply mulch immediately to smother weed seeds. Or, wait about four days and hoe shallowly (1/2 inch) to kill sprouting weeds.
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Weeds are an
index of what
is wrong – and sometimes right – with the soil.
– Charles Walters Jr.
Weeds: Control Without Poisons
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Step 2: Assess the Weed
Know your weed so you can plan an effective control strategy. Is it an annual, which dies down each year and only spreads by seeds (such as chickweed)? Is it a biennial, completing its life cycle in two growing seasons (such as mullein)? Is it a perennial that grows for many years, and reproduces mainly by seeds but also stores food in its roots (such as dandelions)? Or a perennial that spreads by seeds and creeping (such as buttercup or blackberry)? For weed identification, consult WSU Cooperative Extension’s Master Gardeners at 360-786-5445, ext. 7908, Monday through Friday, 9:00 am to 1:00 pm. The Noxious Weed Board can also help identify weeds (see “Weed Disposal,” inside).
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(continued on back)
Himalayan Blackberry
About the Plant: Woody perennial. Spreads by seeds, roots, and by stems rooting where they touch the ground. Manual Control: Pull seedlings. Cut large plants in winter and spring, repeatedly. Dig out with spade. Use mulch in landscaping. Cultural Control: Mow every other week for three years. Encourage wanted vegetation. Heat. Other: The herbicide “Roundup” (glyphosate) can be painted on freshcut stems or regrowth, from midAugust to late September, but no herbicide will completely kill the roots.
Scotch Broom, Spanish Broom
About the Plant: Woody evergreen perennial. Spreads by numerous seeds. Manual Control: Pull seedlings by hand. Use “Weed Wrench” for mature plants. Cut at or below soil surface when flowering. Cultural Control: Keep fields growing a crop. Shade out by planting evergreen trees. Although mowing in spring reduces seed spread, plants will resprout. Note: Dispose of pulled plants in trash to prevent seed spread.
Weed Disposal
Do not compost weeds that regrow from stems, such as English ivy and morning glory. Also do not compost weeds that have gone to seed. You can dispose of 31 different “noxious weeds” free at the Thurston County transfer stations. For help identifying noxious weeds, call the Noxious Weed Control Board at 360-7865576, visit their office at the Thurston County Fairgrounds, or go to www.co.thurston.wa.us/ tcweeds/index.htm
English Ivy
About the Plant: Vigorously spreading woody perennial, evergreen vine. Manual Control: Requires vigilance. Pull by roots and dispose in trash. Cut vines growing up trees to relieve weight in canopy. Cultural Control: Plant understory species such as snowberry, native rose, and sword fern to keep vines from spreading. Note: Do not compost; dispose in trash so vines do not regrow.
Morning Glory (Bindweed)
About the Plant: Perennial that spreads by seed, broken stems, or roots, which travel long distances under the soil. Manual Control: Apply deep mulch after hand pulling or digging all green parts. If coming under fence, dig trench between your property and neighbors’ to pull traveling roots! Requires persistence. Cultural Control: Do not rototill, as the broken stem fragments can resprout. Add lime. Note: Do not compost vines, as they will resprout.
Dandelions
About the Plant: Perennial. Seeds disperse in wind. Regrows from root fragments. Manual Control: Pull in spring and while flowering, before going to seed. Use long tool to dig out whole tap root. Fill bare spots in lawn with grass seed. Cultural Control: Mulch landscaping. Fertilize lawn with a slow-release fertilizer; mow often to 2 inches or higher; water deeply if you do water. Add lime. Use corn gluten as a control (see back page for information).
Grasses
About the Plant: Usually perennial. Cultural Control: For large areas, rototill then mulch or plant. Use a base layer topped by mulch in landscape beds. Install mow strips (barriers made of bricks or boards) to create border between lawn and garden. Other: Use corn gluten in areas where you have not recently planted seeds, and where desirable seedlings are not present.
Buttercup
About the Plant: Perennial, spreads through seeds and stems. Prefers poorly drained, compact soils. Toxic to livestock (depends on amount eaten, species, etc.). Manual Control: Pull and dig. Cultural Control: Fertilize lawn with slow-release fertilizer; aerate, topdress, and overseed (see Common Sense Gardening Natural Lawn Care booklet). Add lime.
Poison Oak Canada Thistles
About the Plant: Perennial. Sends out shoots, some seeds. Manual Control: Cut every two weeks during growing season to less than 3 to 6 inches. Use long tool to reach whole taproot. Hoeing not effective as root fragments can regrow. Cultural Control: Plant species that emerge in cooler temperatures to shade out thistle. Enrich soil with compost. About the Plant: Woody perennial vine or shrub. Spreads by seeds and roots. Manual Control: Dig out rootstocks (wear leather gloves and a longsleeved jacket). Treat with boiling water. Mulch heavily. Other: Goats can destroy large patches of woody weeds; they need proper fencing, water, etc. Paint stems with RoundUp well after the berries have formed but before leaves lose their green color. Note: Don’t burn weed debris.
Horsetail
About the Plant: Spreads by spores and root system that can be as deep as 12 feet. Seeks wet clay soils. Toxic to livestock (depends on amount eaten). Manual Control: Hand pull or hoe tops about 2 weeks after each emergence for 3-4 years. Controlled flaming is temporarily effective. Cultural Control: Landscape fabric plus 4 inches of bark. Dry out wet areas by installing drainage. Note: Persistence is needed to deplete energy reserves.
Step 3: Assess the Site
Why are the weeds present? Weeds generally grow where the soil has been disturbed in some way, or where the desired plants are doing poorly. Find plants suited to the amount of sunshine, type of soil, and amount of care you are prepared to give. Get the Common Sense Gardening Plant List and Plan Before You Plant. (See “For More Information” below.) What level of weeds are you comfortable with? What is it about the weeds that bothers you? Many weeds have good qualities, such as attracting birds and beneficial insects, improving the soil, and having attractive flowers.
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or spread over an established lawn. It is effective against crabgrass, dandelions, and other common weeds, but does not harm soil organisms and other creatures. Do not use on newly seeded areas. Corn gluten is available at many garden centers. Chemical controls: The use of herbicides in home gardens is usually unnecessary. As a last resort, spot applications of herbicides are safer for the environment than broadcast applications. The warning labels on weed and bug killers carry legal definitions: • “caution” = moderately toxic • “warning” = very toxic • “danger” = extremely toxic. Always read labels thoroughly before you buy a chemical product, consider the health and environmental impacts, and carefully follow directions. Thurston County does not use herbicides on roadsides, parks, or other county lands unless the Health Officer has approved their specific use. The county policy does not recommend any herbicide for many types of tough weeds – including morning glory, horsetail, nettles, and poison oak – on county property. Note on “Weed & Feed” products: Usually a mix of an herbicide with a quickrelease fertilizer, these products spread herbicides over a large area, whether there are weeds or not. These chemicals may damage the health of your landscape, wash into local streams and groundwater, and get tracked inside.
Weeding Tips: • It’s easier to pull up weeds in damp soil. • Weed forks make it easier to pull weeds with long tap roots, such as dandelions and Canada thistles (a screwdriver also works). • To save your back, try one of the long-handled, pincer-type weeders with foot pedals or hand triggers. • In lawns, sprinkle grass seeds in the holes left by removing weeds and cover with 1/2” of soil. • Dig or cut perennial weeds just before they bloom, when their food reserves – and ability to regrow – are lowest.
Step 4: Assess Your Options
Hand pulling and hoeing: Hand pulling is very effective for annual weeds before they set seed. It is not as effective for weeds that regrow from root fragments. Hoes are used to chop and scrape out seedling weeds, and expose roots to the drying action of the sun.
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Mowing: Repeated mowing of perennials such as Canada thistle depletes the food reserves stored in plants’ roots. It takes persistence – as in mowing every few weeks during the growing season for at least three years! Mow lawns at least 2 inches high so grass will shade out weeds. Adjust mower height by shifting a lever near the wheels.
For More Information
For more information on gardening topics, including Common Sense Gardening guides to lawn care, root weevils, and aphids, contact Thurston County Environmental Health at 360-754-4111 (TDD line 360-754-2933). The guides are also available free at local nurseries. We welcome your questions and comments. For a list of our publications visit www.co.thurston.wa.us/wwm.
Prepared by the Thurston County Local Hazardous Waste Program with support from the Washington Department of Ecology. January 2002.
Heat: Heat kills weeds. Boiling water from a teakettle can be poured on weeds popping through cracks in the driveway or patio. Propane torches are used to flame tough weeds. Technique is important, as it’s the heat, not actual burning, that kills the plant. Check nurseries, hardware stores, or catalogues for flame weeders. Corn gluten: This natural, nontoxic product keeps seeds from growing roots, and as it decomposes it adds nitrogen to the soil. Use after you have prepared a garden bed
Printed on recycled paper.