How to Kill Grassy Weeds

Annual grassy weeds are quick-growing plants that thrive in the stressed areas of your yard. Thin, dried-out, or sun-scorched areas of your lawn are inviting spots for grassy weeds. The best way to fight them is to kill them before they can make seeds for next year and to maintain your lawn to crowd them out.

What Are Annual Grassy Weeds?

As the name suggests, annual grassy weeds are undesirable plants that look like grass, which can make spotting them difficult. These weeds only live for one growing season, sprouting from seeds in spring when the soil temperatures reach 55-60 °F. Unfortunately, they grow quickly from late spring to summer when they flower and form seed that will sprout the following spring. Annual grassy weeds are killed by the first frost of fall. Grassy weeds reproduce entirely by seed, and they are prolific—each plant can produce thousands of seeds.

The most common annual grassy weeds you'll find in your yard are crabgrass, goosegrass, 

foxtail, and barnyardgrass. 

How to Prevent and Kill Grassy Weeds

Many annual grassy weeds like crabgrass and foxtail can be prevented from developing by applying a pre-emergent herbicide in early to mid-spring. However, once they have sprouted, there are control products available that will kill them later in the year:

• If you only have a few pop-up annual grassy weeds in your lawn, they are best controlled with Ortho® WeedClear™ Weed Killer for Lawns Ready-to-Use.
• If your annual grassy weed problem is widespread, use Ortho® WeedClear™ Weed Killer for Lawns Ready-to-Spray or Ortho® WeedClear™ Weed Killer for Lawns Concentrate applied with an Ortho® Dial N Spray® Hose End Sprayer instead.
• If you also have grassy weeds rearing their ugly heads in your landscape beds, spot-treat them with Ortho® GroundClear® Super Weed & Grass Killer. It is always best to treat annual grassy weeds when they are small and actively growing, before they flower, but this hard-hitting formula will kill them at their roots at any stage (when used as directed).

Always follow all label directions when using any herbicide, and be careful when selecting products—especially when dealing with grassy weeds. Many weed killers also kill or hurt turfgrass, which is why we recommended Ortho® WeedClear™ Weed Killer for Lawns to kill weeds without harming your lawn (when used as directed). It's a good idea to check your product label to make sure your grass is listed for use with that product. Also be aware that weed killers for landscapes and hardscapes like patios may also hurt lawn grasses, so only use these products where directed.

More Ways to Control Grassy Weeds

The way to keep grassy weeds out of your lawn is to make them feel unwelcome in the first place. A thick, lush lawn doesn't leave any space for weeds to grow. To keep annual grassy weeds at bay, follow these maintenance tips:

Mow High. Always mow your lawn at the proper height. For most lawns this is usually one of the highest settings on your mower, but the exact setting varies by grass type. Longer grass blades shade the soil, helping prevent weed seeds from germinating. Scalping your lawn (mowing too short), thins your lawn and makes it more prone to weeds.

Fertilize Regularly. When your lawn is stressed from being under-nourished, it is more prone to being taken over by weeds. Regular feedings every 6-8 weeks during the growing season with a lawn fertilizer helps your lawn stay thick and lush.

Water Deeply. Watering deeply and infrequently—allowing the soil to dry down between waterings—helps your lawn grow deeper roots so it can better compete with weeds. Frequent, quick waterings encourage shallow root growth. During periods of high heat and drought, the grass is more prone to damage causing thin or bare spots that weeds will take advantage of.

Repair Bare Spots. When annual grassy weeds are killed in the fall by frost, they leave behind bare spots. Patching these spots with grass seed will help keep new weeds out. Our friends at Scotts have plenty of options to help you repair your lawn.