The first time my lawn erupted into a sea of purple violets, I actually rather liked it – I tend to evaluate a plant’s beauty first before sealing its doom by calling it a “weed.” For the most part, however, gardeners prefer for their turf grass and their flowers to stay in their respective places and for weeds to stay out of the picture altogether.
While fighting weeds is a year-round job, weed prevention is best practiced in the fall and early spring to take advantage of the growing season of turf grasses. A healthy, thick lawn is your number one defense against weeds. In fact, a badly weed-infested lawn is usually a sign of nutrient imbalance or other soil problems.
For a nice, green lawn that is free of weeds, focus first on getting your grass healthy, then give it a couple of months to become strong before applying weed control products. Minimize turf areas, so that you’re only growing grass where grass easily grows. A small patch of healthy grass is far more attractive than a huge expanse of thin, weedy lawn.
Clover, while good for the soil, is a frequent lawn-invader.
If you’re amending your soil or sowing new grass seed, buy high-quality seed and consider mixing your own soil amendments using only the best ingredients. Pre-mixed topsoil from landscape supply yards often contains weed seeds.
Small patches of weeds can be handled by pulling or digging. All-over lawn weed control is usually not necessary either, as a heavy infestation would be better handled by making the grass healthy. However, for those in-between situations, you may want to consider the use of a chemical or organic herbicide.
Smartweed (polygonum sp.) can take over poorly-drained, moist areas
To choose the correct herbicide, it’s helpful to understand some basic terms that appear on the labels of commercially-packaged weed control products.
- Pre-Emergent herbicides work by preventing seed germination, so they don’t do much good after the weeds are growing. They’re best used as a preventative spot-treatment in known weedy patches, during the winter or summer dormant season.
- Post-Emergent herbicides work by killing growing plants, usually by interrupting chemical processes such as photosynthesis, protein production, or root growth. They are best applied when the plant is actively growing and in the fall when plants are storing up nutrients in their roots. This allows the herbicide to be quickly sucked down into the roots where it is most effective. Post-emergent herbicides can work on contact (killing only the vegetation they touch) or systemic (absorbing into and killing the entire plant).
- Selective herbicides target only certain types of plants by identifying specific enzymes or other plant chemicals. Frequently you’ll see selective herbicides designed to target monocots (such as grasses or other strappy-leaved plants) or dicots (all other plants, often referred to as “broadleaf” plants).
- Nonselective herbicides kill any plant they contact and should be used for spot-treatment only.
- Total vegetation herbicides kill all plants and sterilize the ground for a certain period of time – they should be used very carefully.
So how do these terms work together when shopping for herbicide? Here are some common examples:
- Glyphosphate (found in products such as Roundup) is a post-emergent, nonselective, systemic herbicide. That means it kills any actively growing plants that it contacts. It’s good for spot-treatment but should be used carefully on windy days, especially around roses.
- “Weed & Feed” products (such as Sta-Green Winterizer Weed & Feed) usually contain 2,4-D or other post-emergent, selective herbicides. They’re designed to selectively kill broadleaf weeds without harming grass. However, weed & feed products can kill St. Augustine grass, so check the label to see if it’s safe for this type of lawn before using.
- Trifluralin (contained in products such as Preen Garden Weed Preventer), on the other hand, is a pre-emergent, nonselective herbicide that will kill grass seeds as well as weed seeds and is only for use in established gardens.
- Corn Gluten (found in products such as Concern Weed Prevention Plus) is a natural substance produced by corn that prevents surrounding weeds from growing. It is packaged as an organic pre-emergent herbicide that selectively targets broadleaf weeds.
- Grass killers (such as Ortho Grass-B-Gon) are post-emergent, selective weed killers that target grasses. They are used in flower beds to kill weed grasses.
- Combination Herbicides (such as Ortho Ground Clear) contain more than one post-emergent, nonselective herbicides (such as glyphosphate and imazapyr). Imazapyr is very slow to break down, so this product is designed to kill every plant it contacts and to keep the ground sterile for up to one year.
As with any chemical product, follow package instructions carefully, and only use if absolutely necessary. Herbicides can affect surrounding plants and can pollute ground water when used improperly or in large quantities. By carefully selecting the correct product, you can get rid of those pesky weeds in no time.
My purchased potting-soil often includes “bonus” morning glories.
For more on dealing with weeds in your lawn:
- How to Have a Weed Free Lawn (article)
- Lawn Weed Control (video)
- How to Control Crabgrass (article)
- How to Control Dollarweed (Pennywort) (article)
- How to Control Dandelions (article)
- Vinegar Weed Killer (video)
- How to Target Weeds (video)
For help identifying garden weeds:
- Weed Identification Guide (Virginia Cooperative Extension)
- Common Lawn and Landscape Weed Identification (Landscape America)
For detailed information about specific weeds and control methods:
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