Controlling Weeds

 Complete control of weeds in the home lawn or garden is not a practical goal for many homeowners. A more realistic approach is to minimize weed populations through various control measures. Iowa State University horticulturists provide guidance on weed control methods. To have additional questions answered, contact Hortline, the ISU Extension and Outreach horticulture hotline, at 515-294-3108 or hortline@iastate.edu.
 

How do I control dandelions and other broadleaf weeds in my lawn? 

Good cultural practices are an important key to controlling broadleaf weeds in the lawn. Proper mowing, fertilization and other sound management practices help establish a thick, healthy lawn.  A dense stand of grass provides few opportunities for unwanted weeds. When broadleaf weeds invade lawns, mechanical and chemical measures can be undertaken to remove or destroy the weeds. 

Removing weeds by pulling and digging is an effective control option in small lawns or when only a few weeds are present. This method is best accomplished after a soaking rain or deep watering.

In many situations, herbicides are the only practical method of weed control. Effective broadleaf herbicides include 2,4-D, MCPP, dicamba, triclopyr and others. The most effective broadleaf herbicide products contain a mixture of two or three herbicides as no single compound will control all broadleaf weeds. Fall (late September to early November) is the best time to apply broadleaf herbicides in Iowa. Broadleaf herbicides can be applied as liquids or granules. Before applying any herbicide, carefully read and follow label directions. 
 

How do I control weeds in my garden? 

Cultivation, hand pulling and mulches are the primary means to control weeds in the home garden.

Cultivation and hand pulling effectively control most annual weeds. Perennial weeds are often more difficult to control. Repeated cultivation or the use of herbicides may be 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 rows and pull weeds close to plants. To effectively control weeds, cultivation and hand pulling must be done on a regular basis through the growing season. Small weeds are much easier to control than large weeds. It’s also important to destroy the weeds before they are able to go to seed.  

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 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 rather quickly and can be tilled into the soil in the fall.  
Wood chips and shredded bark are excellent mulches for perennial beds and areas around trees and shrubs. Apply 2 to 4 inches of material around landscape plantings. These materials decay slowly and should last several years. However, it will be necessary to apply additional material periodically to maintain the desired depth.  

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