How to Kill Crabgrass in Your Lawn Once and for All

A weed-free lawn is a goal many homeowners strive for. But there is one plant in particular that can get in the way of that dream: crabgrass. This invasive grass spreads by seed and is characterized by wide leaves that form a tight, crab-like circle. You'll typically see crabgrass pop up during spring and rapidly take over during summer as temperatures ramp up. However, if treated properly, experts say you can kill crabgrass in your lawn before it takes over—and prevent it from coming back.

What Is Crabgrass?

Crabgrass is an invasive warm-season grass that can spread rapidly in favorable conditions. "Crabgrass is a name given to any one of 12 varieties of warm weather annual grass," says Steven Schwager, landscaping manager at Cornerstone Sonoma. The most well-known variety is Digitaria sanguinalis.

Crabgrass seeds germinate as temperatures warm up around the spring and summer. From there, the crabgrass flourishes until it dies and leaves big, circular dead spots of grass. The grass will come right back around the following year from the seeds embedded in your yard if not tended to properly.

How to Get Rid of Crabgrass Before It Forms

The best time to kill crabgrass is in the spring with a pre-emergent herbicide, which prevents weed seeds from taking root. Using a corn gluten based product, either liquid or solid, spray the crabgrass with the pre-emergent herbicide according to the instructions on the product's label, says Craig Elworthy, founder of Lawnbright.

Pre-emergent herbicides kill the weed seeds before they have a chance to appear above the surface. If you time it correctly, a pre-emergent application will significantly reduce the amount of time you spend later in the season dealing with crabgrass. But note that this treatment has no effect on established weeds.

How to Get Rid of Crabgrass After It Forms

If you miss this window, you can also kill crabgrass right after it emerges and is still in the leaf phase. For a larger infestation, try a post-emergent herbicide, which is used to control weeds after they have emerged from the soil. Spray the crabgrass with the post-emergent herbicide according to the instructions on the product's label.

How to Get Rid of Crabgrass By Hand

You can also remove crabgrass by hand once it forms. This method is time consuming, but effective. Using your hands or a garden weeder, pull the crabgrass out of the ground, ensuring the entire root is removed.

How to Prevent Crabgrass

Of course, the best way to keep crabgrass out of your lawn is by preventing it from forming in the first place. "Proper lawn care prevents bare spots and keeps sunlight from the soil so the crabgrass seeds can't sprout," says Schwager. In addition to applying a pre-emergent, there are some other preventative measures you can take to ensure crabgrass doesn't form in your yard.

Mow Regularly

Mowing your lawn regularly has two important benefits: "It encourages grass to thicken up and grow horizontally," says Elworthy. "And it is an effective control for broadleaf weeds, which need to grow quickly and spread their large leaf system to support it." Mowing your lawn often interrupts that process by cutting the weeds off before they can fully develop.

Apply Fertilizer

Thick, dense turf is the best defense against crabgrass. "Fertilizing regularly will thicken up your lawn and crowd out crabgrass and other weeds," says Elworthy. Just make sure you remove all phosphorus from your spring fertilizer applications. "Any added phosphorus will be absorbed by crabgrass and will help speed up its lifecycle," says Elworthy.

Water Deeply

Your lawn needs to be watered deeply and infrequently, which will keep the roots driving deep in search of water. "Most people water their lawn a few times per week for 20 minutes at a time because it's the default setting on their irrigation clock," says Elworthy. "Watering too often and for short periods encourages a shallow, weak root system." This also only waters the top layer of the soil, which benefits shallow rooted weeds like crabgrass.

Reseed Your Lawn

When crabgrass takes over your lawn it crowds out desirable turf grass. "When the crabgrass dies later in the fall, it will leave an ugly brown mess, and lots of bare spots, so you’ll need to thicken up your turf by re-seeding," says Elworthy. "Late August is the best time to seed cool season grasses, so plan on seeding around that time and you’ll have a thick, dense turf by next spring."

Mistakes to Avoid

Even with the right tools and timing, crabgrass control can go wrong if you're not careful. Here are some common mistakes to avoid:

• Rototilling Established Areas: Rototilling can bring dormant crabgrass seeds to the surface, where they'll germinate and create more problems. It's also not 100 percent effective at removing crabgrass and other weeds.
• Applying Pre-Emergent Too Late: If you apply a pre-emergent after crabgrass seeds have germinated, it won't be effective. Apply when soil temperatures reach about 55° Fahrenheit for several consecutive days.
• Failing to Reseed: When crabgrass dies back in the fall, it often leaves behind bare spots. Be sure to reseed these areas to prevent crabgrass from filling in next spring.