Control of weeds in the vegetable garden is important. These unwanted plants are strong competitors for available water, nutrients, and sunlight and can reduce yields when not controlled. Reduced air circulation created by tall weeds encourages the development and spread of foliage diseases and a weedy garden often has more insect problems.
How do I control weeds in my vegetable garden?
Keeping ahead of weeds and controlling them when they are small is essential for good weed management. This requires persistence throughout the entire growing season - from planting until after frost. There are essentially two types of weeds in vegetable gardens, annuals and perennials.
Annual weeds grow rapidly, flower, set seed, and die in a single season. New annual weeds, such as crabgrass, velvetleaf, purslane, knotweed, lambsquarter, and foxtail, germinate from seeds each year.
Perennial weeds die back to ground level in fall but send up new growth in spring. Perennial weeds, such as dandelions, quackgrass, thistle, pokeweed, and plantain, reproduce by seeds and/or may spread by creeping above or below ground stems or roots.
Cultivation, hand pulling, mulches, good cultural practices, and herbicides are the primary means to control weeds in the home vegetable garden.
What mulches work well for weed suppression in the vegetable garden?
Mulches control weeds by preventing the germination of weed seeds. Established weeds should be destroyed prior to the application of the mulch. In addition to weed control, mulches help conserve soil moisture, reduce soil erosion, prevent crusting of the soil surface, keep foliage, fruits, and vegetables clean, and may reduce disease problems.
Grass clippings, shredded leaves, coco hulls, and weed-free straw are excellent mulches for vegetable gardens. Apply several inches of these materials in early June after the soil has warmed sufficiently. Plant growth may be slowed if these materials are applied when soil temperatures are still cool in early spring. These materials break down rather quickly and can be tilled into the soil in the fall.
Newspaper, cardboard, and planters paper can also be successfully used in vegetable gardens as mulch. Avoid the use of waxed cardboard and glossy paper, such as magazines. Remove packing tape and staples from boxes. As with other mulches, start with a weed free area. Over the entire area layout paper four to ten layers thick or cardboard one or two layers thick, being sure to overlap the edges. Cut a hole through the paper or cardboard and plant transplants or seed through it. Then thoroughly wet the paper or cardboard and cover with a layer of mulch or top soil to help hold it in place and prevent it from blowing away. Landscape staples can be used to hold cardboard in place. These paper materials typically breakdown in one growing season and can be tilled into the soil in fall.
Wood chips and shredded bark can be used in the vegetable garden but take several years to decompose. This can be difficult to manage in this setting, especially as it relates to cultivation and planting in future years. For this reason, these mulches are not typically used with annuals like vegetables.
What herbicides can I use in the vegetable garden?
Many home gardeners choose to avoid the use of herbicides in vegetable gardens since they are growing edible crops. Several factors limit the usefulness of herbicides in the vegetable garden. Most vegetable gardens contain a variety of plants in a small area. This restricts herbicide use because it is unlikely that the herbicide will be labeled for all plants in the garden. In certain situations, however, a gardener can use herbicides to supplement other weed control strategies.
Pre-emergent herbicides are used to prevent weed seeds from germinating. They have limited use in the vegetable garden because they will also prevent germination of those vegetable crops that are direct sown in the garden such as beans, lettuce, corn, and others. If only vegetable transplants are used, pre-emergent herbicides can help reduce annual weeds but the timing is important. Consult the label to apply these herbicides at the appropriate time and frequency to control weeds and not impact germination of future seed-driven vegetable crops.
Post-emergent herbicides are used to kill weeds that have already begun growing. They must be carefully applied as they have a high potential to harm both weeds and crops. Always apply herbicides when winds are calm and temperatures or cool to prevent drift and damage to desirable plants. Protect nearby plants with barriers like buckets or boxes to further reduce problems with drift. Herbicides can also be applied with a sponge and wiped onto the leaves of the weed to prevent collateral damage to nearby plants. Herbicides must be used according to label instructions on the package. Failure to follow directions may kill desirable plants or prevent other plants from being grown in the area.
What cultural methods can be used to control weeds in the vegetable garden?
There are several cultural or management techniques the garden can use to reduce weeds in the vegetable garden.
Water plants directly by hand or using soaker hoses or drip irrigation systems. Unlike overhead watering with a sprinkler, this provides water directly
to the plant and does not provide the moisture needed for weed seeds to germinate.
Tilling can help uproot and destroy existing weeds, but it also brings buried and dormant seed to the surface where they are exposed to the sunlight and warm temperatures they need to germinate. Till the vegetable garden two to four weeks prior to planting. This purposefully brings weed seeds to the surface and forces them to germinate early. Right before planting, hoe or lightly cultivate again to kill the newly emerged weeds. Utilize a mulch so the soil does not have to be disturbed again that growing season to prevent new weeds from germinating.
Cover crops also help to reduce weed issues. These fast growing crops are grown to cover the soil when not otherwise planted and can outcompete weeds for nutrients, sunlight, moisture, and space. Cover crops are particularly useful for weed control over the winter months, before planting late-spring or summer vegetables, after vegetable harvest in the fall, or in-between wide-spaced rows. These crops cover the soil preventing germination of weed seeds and when terminated, provide a mulch that further reduces the germination of unwanted plants. Additionally, some cover crops have allopathic properties and produce various substances while they are growing that can prevent the germination or growth of other plants. Cover crops that may work well for home vegetable gardens include, winter rye, winter wheat, buckwheat, rapeseed, annual ryegrass, field peas, oats, oilseed radish, and sweet clover. It is important to grow and terminate cover crops effectively to see their benefits. When not grown properly, cover crops can become difficult weeds themselves. More information about growing cover crops can be found in the following publications: HORT 3026 – Cover Crops in Vegetable Production Systems, HORT 3041 – Short Duration Cover Crops for Vegetable Production Systems
What organic options exist for controlling weeds in my vegetable garden?
Mechanical control of weeds through hand pulling and cultivation as well as the use of mulches and other cultural control methods to suppress weed growth are all effective organic options for weed management.
Pouring boiling water on weeds can be used especially in situations where other plants are not nearby. Be careful to not splash or burn yourself with the boiling water and remember the boiling water will kill both weeds and desirable plants. A tea kettle is often a good way to safely and precisely apply the boiling water directly to the weed. Use plenty of water and plan to retreat 7-10 days later as one application rarely kills the entire plant, especially deep-rooted weeds.
Organic herbicides can also be effective, however, all of them act as non-selective herbicides, meaning they kill or damage any plant part they touch. Many organic herbicides use one or more of the following active ingredients: acetic acid, citric acid, clove oil, lemon grass oil, d-limonene, and ammonium nonanoate, among others. Most organic herbicides work as contact herbicides, killing the leaves and stems, but not being translocated to other parts of the plants, such as roots. Often, multiple applications every 2 to 3 weeks are needed for complete control. Organic herbicides are more effective on younger, smaller weeds than larger more established ones and should be applied at a higher volume than most conventional herbicides, thoroughly soaking leaves to point of run off. Always follow label directions on all herbicides. Even organic herbicides can harm desirable plants or people when used inappropriately.
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