FOR THE LAWN AND GARDEN
Written by: David Johnson, Washington Toxics Coalition
Weed management is probably the most time consuming and frustrating taskfacing the home gardener. No matter what we do, it seems there are alwaysweeds to remove. Plants we define as weeds will always be part of ourlandscapes. It is not realistic to strive for complete elimination. Attemptsto do so usually involve frequent herbicide applications that may haveunacceptable adverse effects on the environment. However, we can managethese pest plants in a manner that minimizes their impact. In order todevelop strategies to outwit them, we need to learn what weeds are and howthey grow.
A weed may be defined as a plant that is not valued where it is growing.Thus, a plant may be considered a weed in one situation and a desirableplant in another. For example, Dutch White Clover is usually a weed inlawns, but it can be a desirable groundcover used to improve soil conditionsand prevent erosion on slopes in new landscapes. The leaves of dandelions,among the more notorious lawn weeds, are valued in salads.
Common chickweed is an annual plant that is easily hand-pulled in gardens.
We can classify weeds by placing them into one of three plant groupsaccording to their life cycle. Annuals germinate, grow, flower, and set seedwithin one year. Biennials produce leaves and store food the first year; thesecond year they flower, produce seed, and die. Perennials live on from yearto year. In many cases the tops will die to the ground, but the rootspersist.
Annuals tend to be opportunistic. They are most often seen colonizingbare soil that has recently been disturbed. Examples of annuals arechickweed, snapweed, and groundsel. Their seed is either blown in or tendsto persist in the soil for years until conditions are right for germination.Many annual weed seeds will germinate after the soil is turned and they areexposed to light. Once they germinate, annual weeds grow very quickly and ina short time are flowering and producing seed for new generations. Biennialweeds, such as foxglove and money plant, are easy to spot in the wintergarden because of their overwintering basal leaves, which form flat clumpswithout a visible stem. The food reserves stored in their thick rootspromote rapid growth in the early spring.
Perennial weeds provide the most difficult challenge. Morning glory,horsetail, quackgrass, and buttercup are perennials which have achievedconsiderable notoriety. The most successful perennial weeds have a thickfleshy root system that stores extensive food reserves. When the leaves areremoved, these reserves quickly provide the energy to produce new ones.
Weed Control: Philosophy and Tactics
An integrated approach to weed management begins with analyzing theproblem. Identify the weeds and determine whether they are annual, biennial,or perennial. Establish a level of tolerance. You need to determine: (a) ifthe weeds are affecting the growth of desirable plants, (b) if theirpresence is an aesthetic problem, and (c) what their potential is forspreading over the entire garden or lawn. You must develop a clear pictureof the problem in order to formulate a strategy to solve it. At this point in the process, we begin to consider specific weed controltactics: (1) mechanical and physical controls, which include mowing,cultivation, burning, and paving; (2) horticultural controls, such asmulching and the establishment of desirable competitive plants; and (3)chemical controls, including both selective and non-selective herbicides.Chemical controls should be used only if the other management techniques arenot adequate. Since most problems involve a mixture of weed types, a mixtureof tactics is often required to achieve effective control
Techniques and Strategies
When considering control options for annual weeds, one has to movequickly to successfully interrupt the cycle of seed production. The presenceof a mulch will deter annual weeds in several ways. It creates a physicalbarrier that blocks light from reaching the soil, prevents seed from comingin contact with the soil, and smothers germinating seed underneath. In areaswhere a thick mulch is not practical, such as in a vegetable garden, it isnecessary to remove weeds frequently before they develop seed and use alight mulch of grass clippings or leaves. Annual weeds can be easily pulledby hand.
Biennial weeds are in many ways easier to control than annual weeds.Their life cycle, extending over two years, provides ample opportunity foreffective control. The overwintering leaves may be rapidly removed with ahoe or by hand pulling. As their flower stalks shoot up in the spring, theymay be easily pulled. If you wait too long, however, the seed will bedispersed and another cycle will begin.
The key to controlling perennial weeds lies in the destruction of theirroot systems by physically digging them out, repeatedly pulling the tops todeplete the food reserves stored in the roots, or, if nothing else willwork, by using the least toxic and most effective herbicide. Once the weedshave been killed or removed, long-term management relies on establishingconditions which do not favor weed growth.
In a vegetable garden, a mix of control tactics may be used. Because ofsoil preparation and harvesting, vegetable gardens frequently contain largeareas of bare, disturbed soil perfect for weed establishment. To inhibitweed growth, it is necessary to shallowly cultivate the soil frequently tokill weed seedlings. Use grass or leaf mulches when possible, and coverunused areas with a living mulch of crimson clover, vetch, or annual ryegrass. Frequent turning of the soil should be discouraged since it can bringdormant weed seed to the surface. Soil amendments can be spread on thesurface and scratched in rather than turned. Use of herbicides isinappropriate near food crops.
Two techniques can reduce the spread of weeds from neighboring yards.Invading roots from morning glory or quackgrass can be turned away byburying a barrier of aluminum flashing under your fence. A depth of about18" should be adequate in most cases, but 24" to 36" may be required forhorsetail. A windbreak of trees or shrubs around your yard will help keepout windblown seeds while it encourages birds.
Plan for the Long-term
The permanent solution for weed control lies in designing out weedhabitats, treating the cause of the problem rather than just the symptoms.Avoid creating conditions that optimize weed growth. Once weeds are clearedfrom an area, apply a 3" to 4" mulch layer and install plantings which willeventually cover the mulch. Mulches are really a short-term solution to weedcontrol, since they eventually break down to form soil in which weeds cangrow. But they do make a good interim barrier to weeds while plants aregetting established, and they can be replenished. Permanent weed managementlies in having a landscape covered with desirable plantings that form amulti-layered groundcover within which weeds cannot get established.
Tools for Weeding
Using the proper tools will make hand-weeding easier and more effective,reducing your need to resort to chemical control.
Hoeing is recommended in vegetable gardens or annual flower beds. Oneeffective type is called a stirrup hoe. The blade is a flat metal loopattached to the handle at an angle that places the blade parallel with thesoil. The blade is moved forward and back just under the soil surface,slicing off weeds at the root line. Any hoe that minimizes soil disturbanceand cuts weeds just under the soil line is more effective than a hoe whichchops them. Chopping weeds tends to pull them from the ground, but the rootsoften remain attached and reestablishment occurs.
These machines are appropriate for cutting down the vegetation in roughareas. They are often used to mow down seed heads before they ripen toprevent seed dispersal.
This material is best used on the surface to smother perennial weeds. Ifused during the summer with the edges sealed with soil, it blocks light andheats the soil underneath to the point where most roots will die. Its use asa permanent barrier under bark mulch is discouraged, since it effectivelyseals the soil from the atmosphere, which can cause a decline in planthealth.
Herbicide Application Tools
If you must resort to an herbicide, don't spray it over whole areas. Usea sponge-type paint brush to apply herbicide directly on the plant leaves.Special wiper tools are also available which do an excellent job. The small,hand-held squirt bottles that come with ready-to-use herbicides can also beused to direct herbicide onto individual plants. Do not use hose-endsprayers. They tend to leak, are difficult to control, and release herbicidetoo rapidly, increasing the chances of inhalation and contact with desirableplants.
Tips for Difficult Weeds
Dandelion is a common perennial weed that invades both lawn and gardenbeds. It becomes established through wind-dispersed seed. Dandelions have along, thick tap root that stores food reserves. Control is achieved by handdigging, making sure that the whole root is removed. In large lawns, this iseasiest with a tool which allows pulling the roots rapidly while working ina standing position. Watering the area first makes it easier to get theentire root. If the root breaks while pulling, the plant can resprout fromthe piece remaining in the soil. To minimize spreading of dandelions, theflowers should not be allowed to go to seed. Mow often to keep the flowersfrom maturing. In lawns, the removal of dandelion plants leaves small bareareas where new weed seed can germinate. Be sure to spread a little grassseed in those spots to prevent weed establishment.
Morning Glory. This weedy vine will twine all over the garden, coveringyour ornamental plants to the point of smothering them. It is usuallyintroduced by seed or invasive roots from under the neighbor's fence. Itssuccess as a weed lies in its thick fleshy roots which travel long distancesjust under the soil surface. It prefers loose organic soils. Since morningglory is a perennial weed, control lies in removing the root system. Handweeding can remove large quantities of roots, but any broken pieces arecapable of sprouting new growth. Repeated, persistent rototilling or flameweeding as the new growth sprouts can deplete the food reserves and allow agroundcover to compete successfully. If chemical control is required, cutback the growth and apply the material to leaves or stems in as localized afashion as possible.
Moss. Moss is a natural part of the Pacific Northwest. It is our nativebottom-story groundcover. If moss is thriving in your lawn, consider leavingit there. Most mosses prefer shade, moisture, and poor, acid soils.Immediate control is achieved by raking it out of lawns or by applying aniron-based product. For long-term control, correcting the conditions thatencourage moss growth is more effective than chemicals. Water infrequentlybut deeply, making sure the water is penetrating and not running off. Properaeration and thatching of lawns will ensure good water retention. Do notapply water faster than the soil can absorb it. Soil should be limed andfertilized to encourage the growth of the desired plants or turf. Considerletting the moss spread in planting beds to form an attractive groundcover.
Clover. Several types of clover are often found in lawns and gardens, andthey do provide certain benefits. The small blossoms form an attractive massof color over large lawn areas. If left in the lawn, clover provides somesoil fertility and attracts bees, which can present a hazard to those usingthe lawn if stepped on. Clovers are legumes and are encouraged by phosphate,potash, and sulfur fertilizers. They can be controlled somewhat withfertilizer high in nitrogen and low in phosphorous. Do not over-fertilize,however, because excess chemicals can run off and contaminate water.
Tips for Least-Toxic Weed Management
- Don't attempt total eradication. Set your weed tolerance at a realisticlevel.
- Identify the weed. For most annual and biennial weeds, mechanical orhorticultural methods should be adequate. Hand pull as much as possible.
- Hire your children or have a weeding party.
- Don't use herbicides as a preventative tactic. Avoid "weed and feed"mixtures.
- For long-term control, design out weed habitats and concentrate on properplant selection and horticulture.
- Do not use herbicides in food gardens. Hoe or hand pull, use grass or leafmulches, plant living mulches, and minimize turning of the soil.
- Chemical control is the last resort. If chemical control is necessary,choose the least-toxic product possible.
- Buy the smallest amount of herbicide you can, even if it costs more perunit. Do not use at greater than recommended concentration or applicationrate. More is not better.
- Do not use broadcast or spray applications. Paint or squirt product directlyonto individual plants or leaves.
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