Managing weeds in the vegetable garden is important for growing healthy and productive plants. Several methods can be used to manage weeds, and in most cases, using several methods together will produce the best results. These methods can be considered "organic" except those that utilize herbicides.
Cultivation and hand pulling effectively control most annual weeds. It is very important to destroy these weeds while they are small before they produce thousands of seeds, guaranteeing a weed problem for many years in the future.
Like annual weeds, perennial weeds are easy to control when in the seedling stage. Once established, they are difficult to control because of their perennial root system and rhizomes. Repeated cultivation of perennial weeds is necessary, being careful not to chop up or leave behind plant pieces that can root to become a new plant, multiplying the problem.
When cultivating the garden, avoid deep tillage. The roots of many desirable plants grow near the soil surface. Deep cultivation will cut off some of these roots. Also, deep cultivation will bring deeply buried weed seeds to the soil surface, where they can germinate. When hand pulling, work in the garden a day or two after a soaking rain or water the garden 24-48 hours before weeding to make pulling and digging easier.
There are several cultural or management techniques the gardener can use to reduce weeds in the vegetable garden.
Proper Plant Spacing
When vegetables are planted at an ideal spacing, the foliage can help shade the ground, reducing weed seed germination and slowing weed growth. When plants are spaced too far apart, weeds more easily grow.
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 seeds 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, forcing them to germinate early. Right before planting, kill the newly emerged weeds without disturbing the soil. Hoeing, light cultivation, flame weeding, and post-emergent or organic herbicides are all options that can be used to kill the recently germinated weeds. This technique of weed control is referred to as the stale seedbed technique. Utilize a mulch so the soil is not disturbed again during 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 beneficial for weed control over the winter months, before planting late spring or summer vegetables, after harvest in the fall, or between wide-spaced rows. These crops cover the soil, preventing the germination of weed seeds and, when terminated, provide a mulch that further reduces the germination of unwanted plants.
Additionally, some cover crops have allelopathic properties and produce various substances while 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
- Annual ryegrass
- Field peas
- Oilseed radish
- 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: Cover Crops in Vegetable Production Systems and Short Duration Cover Crops for Vegetable Production Systems.
Cutting back or mowing off weeds is sometimes used to control weeds in the vegetable garden. Timely or frequent cutting back stresses the weed and reduces its competitive advantage over more desirable plants. Consistent removal of the upper portion of a weed, especially a perennial weed, will prevent weeds from shading nearby desirable plants and slows the growth of the weed.
While weakened, weeds will grow back from the root system. Rarely will the weed be killed by mowing or cutting back alone. When weeds are cut back before they flower and set fruit, it can significantly reduce seed production and reduce new weeds from emerging. This is particularly helpful for annual weeds that persist year to year by starting from new seeds each season - fewer seeds mean fewer weeds in the future.
Mowing or cutting back alone rarely controls weeds completely, but it can be an effective management strategy in combination with other weed control methods, such as utilizing herbicides.
Pouring boiling water on weeds can be used especially in situations where other plants are not nearby, such as in cracks in patios or sidewalks. Boiling water will act as a contact herbicide, killing only the portion of the plant it comes in contact with. It is most effective on young, newly emerged weeds.
Managing weeds with boiling water is an organic option for weed control.
Be careful not to 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.
Flame weeding is the use of intense heat, usually produced by a propane torch or other fuel-burning device, to kill weeds. This organic option for weeding causes the water and sap inside the plant cell to boil and expand rupturing the cell walls and causing the plant to wilt and die.
Flame weeding is most effective on small, young plants. Broadleaf weeds are more completely controlled with this method than grasses. Flame weeding is a particularly effective form of weed control in areas where desirable plants are not nearby, such as in the spaces between pavers or when utilizing the stale seedbed technique for weed management.
For home gardeners, commercially available flame weeder devices can be used, as can handheld propane torches. Safety is of the utmost importance with flame weeding. Always use equipment as directed and do not flame weed on windy days. Never use torches around dry grasses or other materials that could easily ignite. Wear appropriate clothing to protect yourself from the heat and flames.
More information on flame weeding can be found in this article: How to Utilize Flame Weeding for Weed Control.
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
- Weed-free straw
These types of organic materials are excellent mulches. 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 quickly and can be tilled into the soil in the fall or following spring.
- Planters paper
These materials 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, lay paper four to ten layers thick or cardboard one or two layers thick, ensuring the edges overlap. Cut a hole through the paper or cardboard and plant transplants or seed through it. Then, thoroughly wet the paper or cardboard and cover it with a layer of mulch or topsoil 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 break down in one growing season and can be tilled into the soil in the fall or following spring.
Wood Chips & Shredded Bark are Not Recommended
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 annual plants like vegetables.
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 wide 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. However, a gardener can use herbicides to supplement other weed control strategies in certain situations.
Pre-emergent herbicides are used to prevent weed seeds from completing the germination process. They have limited use in the vegetable garden because they will also prevent germination and growth of those vegetable crops directly 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. Herbicides with the active ingredient trifluralin are available to home gardeners and can be used in certain situations. Consult the label to apply these herbicides at the appropriate time and frequency to control weeds and not impact the 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 are cool to prevent drift and damage to desirable plants. Protect nearby plants with barriers like buckets, tarps, 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. Non-selective herbicides with the active ingredient glyphosate are available to home gardeners and can be used in certain situations. Herbicides must be used according to the label instructions on the package. Failure to follow directions may kill desirable plants or prevent other plants from being grown in the area.
Organic herbicides can also be effective, and all 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, lemongrass 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. Multiple applications are often needed every two to three weeks for complete control. Organic herbicides are more effective on younger, smaller weeds than larger, more established ones. They should be applied at a higher volume than most conventional herbicides, thoroughly soaking leaves to the point of runoff. Always follow the label directions on all herbicides. Even organic herbicides can harm desirable plants or people when used inappropriately.