Recognizing Types of Lawn Weeds
By definition, a weed is any plant that grows where you don’t want it to grow. Flowers growing in a lawn or grass growing in a flower bed are considered weeds.
Botanically, there are three types of weeds:
- Broadleaf (dandelions)
- Grassy (crabgrass)
- Grasslike (wild onions)
Weed seeds exist in almost all lawns and gardens, and are 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 since they must reach the soil's surface and receive the proper amount of sunlight and moisture before they germinate and begin to grow.
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.
Controlling Weeds by Promoting Desirable Plants
In the fight to get rid of 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:
- Incorrect watering
- Improper fertilization
- Soil compaction
- Insect damage
- Poor drainage
- Improper sunlight
- Excessive wear on a lawn
To reduce lawn weed problems, 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.
See Basic Lawn Care and Maintenance Tips for instructions on lawn-care practices such as watering, fertilization, aeration, dethatching, mowing and more. Controlling weeds through good lawn care and manual weed removal is part of organic lawn care, which can result in the reduction of chemical runoff entering waterways.
How to Remove Weeds by Hand
Removing unwanted plants by hand or with garden tools is the safest, most selective and environmentally friendly way to control weeds.
The best way to kill weeds in this manner is to deal with them as soon as they show up. Handling the task immediately following a good rain often makes it easier. 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, slim trowel or other handheld weeding tool. Keep the hole as small as possible. Place the end of the tool 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, see Control Pests Without Chemicals Using Integrated Pest Management.
Using Herbicides to Control Weeds
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. Finding the best weed killer depends on how you plan to deal with the weeds.
- Systemic herbicides enter the plant through the roots and leaves, and move throughout the inside of the plant.
- Contact herbicides kill lawn weeds 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. Both types include strong weed killers. The type you use varies by what you’re trying to accomplish and whether or not the weeds are near desirable plants.
- Selective herbicides, when applied as directed by the manufacturer, kill only certain plants. A good example of a broadleaf 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, a feature that can make this type of herbicide the best lawn weed killer. Young, freshly sewn grass would still be susceptible to the herbicide since it wouldn't have had an opportunity to fully establish itself.
- Nonselective herbicides kill plants without discretion, meaning all plants they come into contact with. If you use nonselective weed killer on clover growing in a lawn, it'll kill the clover, but it'll also kill any grass it contacts. In terms of effectiveness, this characteristic can make a nonselective herbicide the best weed and grass killer. For example, you can use these products 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. The timing of pre- and post-emergent herbicide application is critical. Applying them too late or too early is a waste of time and herbicide:
- 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-emergent weed killers establish a chemical barrier that won’t kill established plants but will prevent weeds from successfully growing. The protective barrier breaks down in six to eight weeks, so use of pre-emergents requires proper timing to be effective; apply them very early in the season. Be aware that pre-emergent weed control products can harm some desirable ornamental plants and turfgrasses. As always, read and follow the manufacturer's instructions.
- Post-emergent herbicides are designed to attack weeds that are already established and growing. An example of a post-emergent is a herbicide you use as a crabgrass killer once the weed has sprouted in your lawn. 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.
Weed and feed products — available in granules and liquids — contain both lawn fertilizer and weed killer, and these elements are designed to be released at the appropriate times. To find the best weed and feed product for your yard, thoroughly read the packaging and note the list of weeds the product treats, the type of grass it’s intended for and the proper time for application.
In addition to herbicides that use chemicals to kill weeds, you can find natural herbicides that contain active ingredients such as ammoniated soap of fatty acids — a nonselective, contact herbicide — or corn gluten meal, designed to act as a nonselective, pre-emergent weed killer.
Tips for Controlling Weeds With Herbicides
Remember these key points when using herbicides for weed control:
- Read all herbicide labels. Find out whether you're applying a selective or nonselective herbicide. Since selective herbicides target a specific type of weed, you can apply them more liberally. Nonselective herbicides will kill any plant; so apply these carefully and only to plants you want to kill.
- Mark your containers. Use a permanent marker to designate specific spray bottles and sprayers for herbicides and keep separate containers for watering.
- Don't mow or prune before product application. More available leaf surface on the weed is better for absorbing the herbicide.
- Don't mow or prune for several days after herbicide application. This will give the plants time to absorb the chemical.
- Focus on young, actively growing plants. Apply herbicides to younger plants to stop rampant growth before it starts. Older plants may require stronger weed killers or multiple applications.
- Make sure the plants you want to keep are mature enough to withstand the effects of the chemical. Desirable young plants may not be able to fight off the effects of most herbicides.
- You can treat large areas with a hose-end attachment. You can also apply granular herbicides with a broadcast or drop spreader.
- After plants have germinated, spot treatment is the best choice to avoid chemical damage to desirable plants. Use a spray herbicide for spot weeding. Apply directly onto the weed to kill the entire plant. Repeat as necessary and don't apply to the lawn.
- Avoid applying chemicals on windy days. The chemical may drift or run onto desirable plants and flowers, killing them as well.
- Don't discard weeds and clippings where the weeds can spread to other planting areas.
Weed Control With Herbicides and Safety
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:
- Closely follow the herbicide manufacturer's instructions, including those for use, safety, clothing, protective gear, storage and disposal. Failure to follow the manufacturer's recommendations can increase the dangers associated with use of the chemicals and decrease their effectiveness.
- Always wear gloves appropriate for the herbicide you're using in addition to long pants, a long-sleeved shirt, rubber boots and any safety gear specified by the herbicide manufacturer when applying these chemicals. Wash out all clothing after use.
- Be sure to use only the recommended amount of herbicide to prevent buildup in water tables that can harm the environment.
- After application, keep children and pets off a treated area according to the product instructions.
- Store chemicals in a cool, dry and dark place safely out of children's reach.
Weed Control Schedule
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.