Vegetable Garden Weed Control

Weeds are unwanted plants in gardens that reduce available moisture, nutrients, sunlight, and growing space needed by crop plants. Their presence can reduce crop growth, quality, and yield. In addition, they can make harvest difficult. Weeds also provide cover for diseases, insects, and animals (rodents, box turtles, snakes, etc.). Gardenweeds are hard to control because they grow rapidly, produce vast numbers of seeds, and spread aggressively by vegetative structures and/or seeds. A combination of cultural and mechanical weed control methods can be quite effective in controlling weeds.

Cultural Methods

Fast growing vegetable crops can effectively suppress weeds by shading them. One method of weed control is to select a crop that is capable of suppressing weeds through shading. The following vegetable crops are listed according to their ability to suppress weeds. Crops that are good weed suppressors are: squash, beans, pumpkins, ,southern peas, cucumbers, sweet corn, melons, Irish potatoes, sweet potatoes, and tomatoes.

Suppression of weeds by crops works best when the crop germinates quickly and gets a head-start on weeds. To achieve this, plant crops at the proper depth, with adequate moisture and fertilizer. It is equally important to purchase high quality vegetable seeds or transplants that are free of weed seeds or seedlings. Garden soils should be tested and soil test recommendations followed to stimulate rapid crop growth capable of weed suppression.

Fast growing 'smother' crops can be used to reduce weed germination in succeeding crops. For this purpose, smother crops are usually planted in the fall and killed by tillage the following spring prior to planting vegetables. The straw residue from smother crops (i.e. rye, ryegrass, etc.) can inhibit early season germination of weeds such as common lambsquarters and common purslane by 75% or more.

NOTE: Avoid planting smother crops where small seeded crops such as lettuce will be seeded the following year or reduction in germination can occur. Smother crops are also effective in suppression of many winter annual weeds, such as henbit and chickweed. Rotate crops to different areas of the garden so that a specific crop is never planted in one area for two years in a row.

Mulches can be used to prevent weed germination and growth and ultimately reduce time and labor required to remove weeds. Mulching help to increase soil moisture retention, enhance soil warming and reduce weeds. The decision of whether to use an organic or an inorganic mulch depends on the season and what the gardener is trying  to accomplish. Organic mulches should be applied after the soil temperature has warmed in the spring. If applied to cold soils, the soil will warm slowly and the growth rate of most vegetables will be reduced. Inorganic mulches can increase the soil temperature by at least 6 to 8oF, making their value greatest early in the growing seasonwhen soils are naturally cool.

Organic mulches: Some of the most commonly used organic mulching materials are manures, bark chips, ground corncobs, sawdust, grass clippings, leaves, newspapers (shredded or in layers), and straw. Organic mulches allow some flexibility in fertilizing and watering since they can be raked back from the plants. They should normally be applied in a uniform layer 3 to 4 inches deep around the base of the vegetable plant.

Inorganic mulches: Black plastic is the most frequently used inorganic mulch. Clear plastic is not recommended because it does not exclude the light that weed seeds need to germinate. Verify that there is adequate moisture in the soil before any mulch is applied, especially plastic films. It is also necessary to apply most of the fertilizer required by the plants before the plastic is installed. There are also several durable weed fabrics that are very effective in weed suppression. They are capable of lasting up to 20 years or more when covered with soil.

Mechanical Methods

Since emerged weeds present at seeding or transplanting are capable of growing rapidly, it is important to kill all weeds prior to planting. Weeds that emerge after planting should be removed before they are more than 3 inches tall. Large weeds are difficult to remove without uprooting vegetable plants. Early season competition between vegetables and weeds may reduce crop growth, yield, and quality. Manual removal by hand or with hand tools or cultivation are two methods to rid the garden of weeds.

Several small hand tools are available that are very effective on small weeds and for working near garden plants. They include the springtooth hand cultivator and the trowel, both of which limit the gardener to working on their knees. However, there are a number of effective tools that the gardener can stand to use, including the scuffle hoe, the Warren hoe, and the onion hoe.

Scuffle hoes come in several shapes and act as "push-pull" weeders that require no lifting. One of the most popular is the Dutch version, which is an open stirrup with a blade. Others consist of triangular plates. Most scuffle hoes are lightweight and are effective on small weeds.

The Warren hoe has an arrowhead shape and can be used to scratch a furrow with one end; when turned upside down the two shoulder points fill in the furrow.

The onion hoe is a thin bladed hoe that is recommended when removing weeds near vegetable plants as it is easier to handle than large, heavy hoes. Onion hoes can be made by grinding a common hoe so that the blade is thin, allowing more precise maneuvering near vegetable plants.

Push plows, also called push cultivators, are inexpensive and also very effective in killing small weeds. The large wheel versions are usually easiest to push. For large weeds, a garden tiller or small tractor is most effective. Regardless of the implement, cultivate no deeper than 2 inches deep to prevent root damage to vegetable plants. Cultivators should normally be adjusted to throw soil around the base of crop plants and over any emerged weeds that are present in the row. Row spacing can be adjusted to allow close mowing near the soil surface to control weeds. Self-propelled rotary or sicklebar mowers and/or mowers with large rear wheels are easiest to maneuver. Weedeaters fitted with plastic string can also be used to cut weeds near the soil surface. Extreme care should be used for crop and personal safety.

Adapted from David W. Monks and Larry Bass, North Carolina Cooperative Extension Service, 2000