I was talking with my friend, Jim Campbell, manager of Bi Lo Supply, about controlling weeds in his garden.
Weeds compete with desirable plants for water, nutrients, sunlight and growing space and can reduce yields of fruits and vegetables. Their control also enhances the performance of annual and perennial flowers.
You need to first identify the weeds, since this helps determine the best method of control. There are annual and perennial weeds. Annual weeds germinate, grow, flower, set seed and die within one year. Perennial weeds live for two or more years. They often die in the fall, but sprout from their roots in the spring. Weeds can also be classified as broadleaf weeds or grasses.
Three general methods of weed control are available to the home gardener: cultivation and hand pulling, mulching and herbicides. By far the most common methods of weed control in the home garden are cultivation and hand pulling and
mulching. Hoeing, rototilling, and hand pulling will effectively control most annual weeds, but often-repeated cultivation is needed to kill many perennial weeds.
When cultivating the garden, avoid deep tillage since the roots of many vegetables, fruits, and flowers grow near the soil surface and 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. Hoeing, rototilling, and hand pulling should be started early in season since small weeds are easier to control
than large weeds.
Some perennial weeds, such as quackgrass, are extremely difficult to control in the home garden. Quackgrass is a perennial grass that spreads rapidly by underground stems or rhizomes. Rototilling an area infested with quackgrass will simply cut up the rhizomes and spread the weed. To effectively control quackgrass, all the rhizomes must be carefully removed from the soil.
Mulches control weeds by preventing weed seed germination. Mulches control most annual weeds. Perennial weeds, however, must be controlled by other methods. In addition to weed control, mulches help conserve soil moisture, reduce soil erosion, prevent crusting of the soil surface, keep fruits and vegetables clean, and may reduce disease problems.
Grass clippings, shredded leaves, and straw are excellent organic mulches for vegetable gardens and annual flower beds. Destroy all weeds prior to mulching. Apply 4 to 6 inches of these materials in early June after the soil has warmed sufficiently. Plant growth may be slowed if organic mulches are applied when soil temperatures are still cool in early spring. Grass clippings, shredded leaves, and similar materials break down relatively quickly and can be tilled into the soil in the fall.
Wood chips and shredded bark are excellent mulches for landscape plantings. Apply 2 to 4 inches of material around landscape plantings. These materials decay slowly and should last several years.
Black plastic mulch is excellent for use in the vegetable garden. Plants or seeds are set in holes made in the plastic. Black plastic controls weeds, but it also increases soil temperatures in the spring and conserves moisture. Black plastic is not recommended for landscape plantings. Plastics can trap excessive amounts of water in the soil during wet weather, damaging the roots of trees and shrubs. Landscape fabric, however, can be used around trees and shrubs, as these materials allow water and air to pass through them. The landscape fabric should be placed on the ground and then covered with wood chips or shredded bark.
Herbicides can be used to help control weeds in the home garden but should be used to supplement cultivation and hand pulling since there is no single herbicide that can be used to control weeds in all vegetables and flowers and different herbicides often have to be applied to the various crop areas. Also application methods and times may vary for different crops and herbicides often control some types of weeds, but may have little or no effect on others.
For example, Preen (trifluralin) effectively controls most annual grasses, but doesn’t control many broadleaf weeds. Always read the label directions carefully for specific recommendations.
An excellent resource on this subject can be found at Cornell University www.gardening.cornell.edu/pests/ pdfs/weedcontrol.pdf .
Bill Lamont is a professor and extension vegetable specialist in the Department of Horticulture, Penn State. He can be reached by at wlamont@psu.edu.
