Need to defend your turf from crabgrass? Follow these tips and learn how to kill crabgrass and be one step closer to having a perfect lawn.
Our editors and experts handpick every product we feature. We may earn a commission from your purchases.Learn more.
Crabgrass is a tough opponent, but with a lawn spreader, a pump sprayer and a few turf products you can get rid of crabgrass in the spring and control it throughout the summer.
The best weapon in your quest to kill weeds like crabgrass is pre-emergence herbicide (also called crabgrass preventer). Apply it in the spring before the crabgrass seeds sprout. The granular herbicide works by creating a chemical barrier at the surface of the soil. As the seeds germinate, they take in the herbicide and die.
If you have a particularly bad weed problem, one application per season may not be enough to get rid of crabgrass. Chances are the crabgrass will germinate and spring up later in the summer.
Pre-emergence herbicides have a lifespan of about 50 days after application (check the label; product lifespans vary). Once the chemical barrier breaks down, dormant crabgrass seeds, which can remain viable for years, may germinate into seedlings. Even if you successfully get rid of your crabgrass, if your yard butts up against property that has a thriving crabgrass crop, you can bet thousands of your neighbor’s weed seeds will blow onto your lawn just when your herbicide is calling it quits.
You don’t need to reapply herbicide to your whole yard. Concentrate your re-application efforts on areas where crabgrass thrives, like the edges of driveways and walking paths. These spots tend to absorb more heat, warming the soil and making for prime crabgrass locations.
Spray post-emergence herbicide directly on crabgrass after it has sprouted. Pulling is equally effective, but if the roots are deeply embedded in your lawn, it may be tough to pull them out without pulling grass chunks, too. It’s not worth spraying a post-emergence product on crabgrass that has gone to seed. It takes about two weeks for the herbicide to work, which is about how long it takes the plant to finish its seeding process. If it has gone to seed, you’re better off waiting for next spring and applying a pre-emergence product then.
Post-emergence herbicides are most effective when the soil is moist and the plants are dry. Read the post-emergent crabgrass killer label for specific instructions. Typically you apply it with a hand pump sprayer. It’s best to apply it on a hot day when there’s low wind. If temperatures are too low, the product may be ineffective. Unless the crabgrass is young, you’ll probably have to reapply post-emergent crabgrass killer a few days later (according to the label) to kill the plant.
After post-emergence application(s), keep an eye on the treated area. In extremely dry conditions, water two days after the application to aid absorption. If your grass near the treated area is turning brown, you probably were a little heavy-handed. Soak the damaged area with water to dilute the chemical and avoid further damage. Also, be on the lookout for new crabgrass sprouts. These will require another herbicide treatment, or if there aren’t too many, simply pull them. Be sure to seed these areas in the fall.
Crabgrass in the fall. Don’t waste your money on a post-emergence herbicide in the fall as a route on how to kill crabgrass, when the temperatures are falling. The herbicide won’t be effective and the plant will soon die anyway.
Pre-emergent herbicides are the most effective and economical way to control weeds and crabgrass. But if you’d rather not use herbicides, you can try hand-weeding individual crabgrass plants in late spring before they get too big. They pull easily in the soft ground after a rain.
Corn gluten meal (CGM), a corn byproduct, is another method used to control crabgrass and broadleaf weeds such as dandelions and clover. It releases a protein that slows the development of weed seedling roots. CGM requires a heavy application rate (20 lbs. per 1,000 sq. ft.), which makes it cumbersome to use and expensive. It costs about $30 for 25 lbs. at garden centers.
