How to Kill Crabgrass in Your Lawn Once and for All - Martha Stewart

A weed-free lawn is a goal many homeowners strive for. But there is one plant in particular that can wreak havoc on your yard annually: crabgrass. This weed spreads by seeds and is characterized by wide leaves that form a tight, crab-like circle. You'll typically see crabgrass pop up during spring and rapidly takeover during summer as temperatures ramp up. However, if treated properly, 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 from the weed 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 weeds will come right back around the following year from the seeds embedded in your yard if not tended to properly.

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When to Kill Crabgrass

Timing is everything when it comes to killing crabgrass. "You have a small window of a few weeks where crabgrass is really vulnerable. Otherwise, you're playing catchup for the rest of the year," says Craig Elworthy, founder of Lawnbright, a DIY lawn care subscription company.

Before It Forms

Generally, the best time to kill crabgrass is in the spring with a pre-emergent herbicide. "A pre-emergent herbicide prevents seeds from taking root," says Elworthy. "It kills before the weed has a chance to appear above the surface, and it has no effect on established weeds." 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.

After It Forms

If you miss this window, you can also kill crabgrass right after it emerges and is still in the leaf phase. During this phase, it's easy to pull the weeds out by hand. For a larger infestation, try a post-emergent herbicide, which is used to control weeds after they have emerged from the soil.

There is a point, however, when removing existing crabgrass does more harm than good: "If the crabgrass has put out seed heads, you should probably just leave it, as trying to pull it now would only drop new seeds into the hole left behind, ensuring a new plant will grow in the exact spot next year," says Elworthy.

How to Kill Crabgass

Killing crabgrass before it forms is ideal and can be done using an organic pre-emergent herbicide. This still allows the seeds to germinate, but they won't be able to develop a root system, which will ultimately kill off the plant before it appears, says Elworthy. Use a corn gluten based product, either liquid or solid, and make sure to apply it during spring. Spray the crabgrass with the pre-emergent herbicide according to the instructions on the product's label. Mow your lawn regularly to prevent weeds from popping up.

If you see any crabgrass forming after using a pre-emergent herbicide, pull it as early as possible to prevent it from dropping seeds for next year. "Make sure that you reseed the bare patches created when the crabgrass is removed to create inhospitable conditions for the crabgrass," says Schwager.

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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.

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