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Weeds are a common challenge around the home landscape. Even the best landscapers and gardeners must deal with these persistent pests. There are, however, proven methods for reducing and controlling weeds.
By definition, a weed is any plant that is growing where you do not want it to grow. Flowers growing in the lawn or grass growing in the flower bed would be considered weeds. Botanically, there are three types of weeds:
Weed seeds exist in almost all lawns and gardens, and spread in a number of ways. They can be dispersed by wind, water, animals, soil amendments, poor quality grass seed and lawn and garden equipment. Many weed seeds remain dormant for years before they begin to grow, since they must reach the soil's surface and receive the proper amount of sunlight and moisture before they germinate.
There are three main classifications of weeds:
Annuals normally grow, produce seeds and die within a single year. In warmer climates, some annuals may survive a second year. In general, annual weeds are the easiest to kill.
Biennials live for two years. Biennials devote the first year to vegetative development and the second year to flowering and seed development.
Perennials live from season to season and produce seeds each year.
In the fight against weeds, the most important element is to promote the best environment possible for the growth of desirable vegetation. There are a variety of lawn and garden conditions that can discourage desirable plants, increasing the potential for weed development:
To reduce lawn weed problems, it is also important to mow the grass at the proper height. Mowing the lawn too short decreases the grass's ability to shade the soil from sunlight, thereby increasing the potential for weed germination.
Removing unwanted plants by hand or with garden tools is the safest, most selective and environmentally friendly way to control weeds.
You can remove weeds at any time, but immediately following a good rain often makes it easier. Attack a weed as soon as it shows up. Pull the weed close to the base, lifting out as much root as possible.
For larger weeds with extensive roots, like thistles and dandelions, use a garden fork, spike or slim trowel. Keep the hole as small as possible. Place the end close to the weed's base and plunge it deep into the ground. Loosen the surrounding soil. Grab the weed under its crown and pull out the entire root.
For best results in pest control (including weed control) with minimal chemical use, consider following an Integrated Pest Management schedule. For more information see Control Pests in the Garden without Chemicals.
Manual weed removal may not be practical for large lawns and gardens or for areas overgrown with many weeds. In these cases, you may choose to use herbicides. When you apply them properly, herbicides are very effective at eliminating weeds. Herbicides are available in two main categories:
Systemic herbicides enter the plant through the roots and leaves and move throughout the inside of the plant.
Contact herbicides kill from the outside in. They attack the exposed parts of the plant, killing the weed by reducing its ability to feed itself through photosynthesis.
Within these two categories, herbicides may also be selective or nonselective:
Selective herbicides, when you apply them as directed by the manufacturer, kill only certain plants. A good example of a selective herbicide is a lawn weed killer designed specifically for the removal of broadleaf plants. These products will remove the weeds without killing the established lawn in which the weeds grow. Young, freshly sewn grass would still be susceptible to the herbicide however, since it would not have had an opportunity to fully establish itself.
Nonselective herbicides kill plants without discretion. They will kill all plants they come into contact with. You can use these products, for example, when preparing an area for planting or when attempting to establish a new lawn. Through their use, all living vegetation — including problem plants — can be removed from an area, giving the gardener a clean slate with which to work.
Finally, herbicides are either pre-emergent or post-emergent.
Pre-emergent herbicides are designed for application before the targeted weed germinates, and are an effective preventative method for controlling weeds. Crabgrass preventer is a good example. Pre-emergents establish a chemical barrier that will not kill established plants, but will prevent weeds from successfully growing. The protective barrier breaks down in six to eight weeks. Use of a pre-emergent, therefore, requires proper timing to be effective – apply them very early in the season. Be aware that pre-emergents can harm some desirable ornamental plants and turf grasses. As always, read and follow the manufacturer's instructions.
Post-emergent herbicides are designed to attack weeds that are already established and growing. All of the contact weed killers are post-emergents. Apply post-emergents later in the growing season, after weeds are established but before they have gone to seed.
The timing of pre- and post-emergent herbicide application is critical. Applying them too later or too early is basically a waste of time and the herbicide.
Remember these key points when using herbicides for weed control:
Herbicides can be effective in controlling weeds, but be careful to handle these powerful chemicals properly and safely. For safety and to see the maximum benefits of the product:
Like lawn and garden care, weed control duties extend through different seasons.
Early spring - Inspect your lawn as spring approaches and then decide on the treatment. If you're using herbicide, apply a pre-emergent shortly before annual weeds, such as crabgrass, begin to grow in the spring. A good rule is to apply the pre-emergent before the dogwoods begin to bloom. You may decide to use a pre-emergent combined with fertilizer as an early lawn treatment.
Late spring - In the middle of the growing season, determine which weeds have come back and repeat weed killer application or remove weeds selectively with herbicide or by hand.
Fall – If you're using herbicide, treat your lawn one last time with a general weed killer after the final mowing. Remove large weeds by hand to ensure they will not survive over the winter.