What's Up In The Garden

by Jackie Dohlman, Franklin County Master Gardener

Tips on Controlling Weeds in the Garden

Weeds are those annoying plants that gardeners love to hate. In the garden, weeds compete with desirable plants for water, nutrients, sunlight and growing space. They also may harbor insects and diseases. Allowed to run rampant in the garden, weeds can drastically reduce yields of fruits and vegetables. In addition, they hinder the performance of annual and perennial flowers.

The first step in weed control is identification of the weed or weeds. The type of weed helps determine the best method of control. The two main types of weeds are annuals and perennials. Annual weeds germinate from seeds, grow, flower, set seed and die within one year. Perennial weeds live for three or more years. Most perennial weeds die back to the ground in fall, but their crowns or roots produce new shoots in spring. Weeds also can be classified as broadleaf weeds or grasses.

There are three general methods of weed control in the home garden: cultivation (hoeing and tilling) and hand pulling, mulches and herbicides.

Cultivation and hand pulling effectively control most annual weeds. Perennial weeds are often more difficult to control. Repeated cultivation is often necessary to destroy some perennial weeds. When cultivating the garden, avoid deep tillage. The roots of many vegetables, fruits and flowers 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. Hoe or till around plants or between plant rows, and pull weeds close to plants.

To effectively control weeds, cultivation and hand pulling must be done periodically through the growing season. Small weeds are much easier to control than large weeds. It’s also important to destroy the weeds before they have a chance to go to seed.

Mulches control weeds by preventing the germination of annual and perennial 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 fruits and vegetables clean and may reduce disease problems.

Grass clippings, shredded leaves and weed-free straw are excellent mulches for vegetable gardens and annual flower beds. 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. Grass clippings, shredded leaves and similar materials break down relatively quickly and can be tilled into the soil in fall.

Wood chips and shredded bark are excellent mulches for perennial beds and areas around trees and shrubs. Apply two to four inches of material around landscape plantings. These materials decay slowly and should last a few years. However, it’s often necessary to apply additional material annually to retain the desired depth.

Herbicides can be used to supplement cultivation, hand pulling and mulches. However, several limitations prevent the extensive use of herbicides in the garden. Only a small number of herbicides are available to home gardeners. Additionally, most home gardens contain a wide variety of fruits, vegetables and flowers. No one herbicide can be safely used around all garden and landscape plants. If not applied properly, herbicides may cause unintended damage to fruits, vegetables and ornamentals. Herbicides are pesticides. When using any pesticide, carefully read and follow label directions.

Weeds are a persistent problem for home gardeners. However, weeds can be effectively controlled by cultivation, hand pulling, mulches and (on occasion) herbicides. Persistence is the key. Gardeners need to be as persistent with their weed control efforts as weeds are in coming back again, and again and again.

Got gardening questions? Contact the Hortline at (515) 294-3108 (Monday - Friday; 10 a.m. -12 noon and 1 - 4:30 p.m.) or send an e-mail to hortline@iastate.edu. For more gardening information visit us at Yard and Garden Online at www.yardandgarden.extension.iastate.edu