B. Rosie Lerner
Extension Consumer Horticulture Specialist
No matter what kind of garden you tend, weeds are likely one of your more frustrating challenges. However, there are a number of practices you can incorporate in your bag of tricks to keep weeds under control.
Cultural control includes any gardening practice that prevents the introduction of weeds to the garden or makes the environment less favorable for weed development and more favorable for desirable plants. Controlling weeds before they mature their seed will help prevent future weeds. For example, a single dandelion plant can produce 15,000 seeds in one year, and each seed is capable of surviving up to six years in the soil.
Thorough preparation of a planting site is crucial to getting your garden off to a good start, especially where perennial weeds have gained a foothold. Till existing weeds under or use a nonselective herbicide to kill them. As an alternative to using chemicals, many gardeners have had success using a clear plastic cover to heat soil to the point of killing existing weeds. Depending on weather and stage of plant growth, both chemical and solar methods can take several days to weeks to kill the undesirable vegetation.
Use a mulch wherever possible to prevent weed seeds from germinating. Organic mulches include pine needles, bark chips, grass clippings and straw. Organic mulches have the additional benefit of improving soil structure and adding some nutrients when they are worked into the soil at the end of the season. They also tend to cool the soil while they conserve moisture. Be sure your mulch is free of weed seeds, especially when using straw and hay, or you may end up with more weeds than you started with.
Plastic mulches are excellent for preventing weed germination and conserving soil moisture. Black plastic tends to warm the soil, which is beneficial for warm-season crops, such as tomatoes and peppers. White plastic also works well as a mulch, but it does not have as much effect on soil temperature as black plastic. Recent studies have found that other colors of plastic, particularly red, may enhance plant growth. Clear plastic should not be used since it allows light to penetrate, resulting in germination of weed seeds and excessive heating.
Plastic has long been used under other mulch materials in landscape plantings to help keep weeds out of the ornamentals. But poor water penetration has been a problem in such long-term plantings. Fabric mulches made of either spun or woven plastic cloth have been developed recently. Fabric mulch is especially useful for landscapes where good water penetration is a big boost. As a garden mulch, fabrics do provide good early-season weed protection. However, because fabrics allow some light to penetrate, weeds will germinate below and break through the cover unless some other material, such as rocks or bark mulch, are placed on top.
Hoeing can be very effective for controlling annual weeds. However, perennials often resprout from the roots after the tops are removed. Hoeing should consist of short, shallow strokes that simply cut off the weeds at soil level. Hoeing deeper will only bring more weed seeds to the germination zone and may injure the roots of desirable plants growing nearby. Weeds growing in close proximity to desirable plants should be hand-pulled. Weeds will be much easier to pull or hoe while they are still small.
Chemical weed control is better suited to the large-scale commercial grower than to the home gardener. Most herbicides are not available in a convenient size for home-users and are quite expensive to purchase in commercial grower-sized packages. However there are a few chemicals available from garden suppliers that can be used with caution. Herbicides must be chosen carefully based on both the weed problems and the desirable plants involved. Remember, no one herbicide will control all weeds in all desirable plantings. Look at the herbicide label for information such as weeds controlled, plants on which the chemical can be safely used, rates of application and precautions. Always read the label on any pesticide before you apply!
And finally, promoting healthy growth of desirable plants through proper watering and fertilizing techniques will make those plants more competitive with weed species. Most plants grow best with about an inch of water per week. Just about any balanced-analysis fertilizer can be used for garden or landscape plants if applied according to label directions.
The URL for this page is http://www.hort.purdue.edu/ext/weeds.html