How to Get Rid of Crabgrass (and Prevent It)

Crabgrass is the lawn weed almost everyone recognizes but few people defeat for good. It germinates by the thousands every spring, sprawls into ugly star-shaped clumps by midsummer, then dies in the first hard frost after dropping a fresh batch of seeds for next year. The good news: once you understand its life cycle, crabgrass becomes one of the easiest weeds to control. This guide walks you through identifying it, stopping it before it sprouts, killing what’s already there, and building the kind of thick lawn that crowds it out for good.

In this guide

1. How to identify crabgrass
2. Why crabgrass invades thin, short lawns
3. Pre-emergent timing: the single most important step
4. Killing crabgrass that’s already growing
5. The best long-term fix: a thick, healthy lawn
6. A season-by-season crabgrass plan
7. Frequently asked questions

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How to identify crabgrass

Before you spend money treating it, make sure you’re actually dealing with crabgrass and not a look-alike like tall fescue clumps, quackgrass, or goosegrass. Crabgrass is a warm-season annual, which means it sprouts new from seed every spring, thrives in summer heat, and dies completely in fall.

What to look for

• Growth habit: Low, spreading clumps that radiate outward from a central point like the legs of a crab or the spokes of a wheel.
• Blades: Wider and a lighter, more yellow-green than most turf grasses, often with a slightly hairy base.
• Stems: Coarse, branching stems that lie flat against the ground and root where the joints touch soil.
• Seed heads: Finger-like spikes (usually 3 to 9) that fan out from the tip of the stem in mid to late summer.
• Location: Almost always shows up first along driveways, sidewalks, and thin or bare spots where the soil heats up fastest.

If the weed comes back from the same root crown every year, it’s a perennial and not crabgrass. For a broader rundown of the weeds that plague American lawns, see our guide on how to get rid of lawn weeds.

Why crabgrass invades thin, short lawns

Crabgrass isn’t a sign of bad luck. It’s a sign that something is letting its seeds germinate. Those seeds are already sitting in your soil, and they only sprout when two conditions are met: warm soil and sunlight reaching the seed.

• Mowing too short: Scalping the lawn lets sunlight hit the soil surface, which is exactly the trigger crabgrass seeds need to germinate.
• Thin or bare patches: Any gap in the turf is an open invitation. Crabgrass colonizes empty soil before your grass can fill it in.
• Compacted, stressed soil: Hard-packed areas along walkways favor crabgrass over fine turf grasses.
• Shallow, frequent watering: Light sprinkles keep the surface moist and warm, encouraging shallow-rooted crabgrass while starving deep grass roots.

The takeaway: every cultural mistake that thins or shortens your lawn hands crabgrass an advantage. Fix those, and you remove the conditions it needs to spread.

Pre-emergent timing: the single most important step

A pre-emergent herbicide creates a chemical barrier in the top layer of soil that stops crabgrass seeds from establishing as they germinate. It does nothing to crabgrass that has already sprouted, so timing is everything. Apply too late and the seeds are already up; apply too early and the barrier can break down before the main germination window.

Nail the timing with soil temperature

• The magic number: Crabgrass begins germinating when soil temperatures at a 1 to 2 inch depth hold around 55 degrees F for several consecutive days. Apply your pre-emergent before the soil reaches that point.
• The forsythia rule: An old gardener’s trick that actually works. Apply pre-emergent when forsythia shrubs are in full bloom and just starting to drop their yellow flowers. Forsythia and crabgrass respond to the same warming cues.
• Measure, don’t guess: A simple soil thermometer takes the guesswork out completely. Check mid-morning over several days.
• Regional range: In the warm South this can mean February or early March; across the North it’s often April into early May.

Application tips

• Choose a quality crabgrass pre-emergent and spread it evenly with a calibrated broadcast or drop spreader.
• Water it in with about a quarter to half inch of irrigation within 48 hours to activate the barrier.
• In long, hot climates a second “split” application 6 to 8 weeks later extends protection through the full germination season.
• Critical exception: Pre-emergents stop all seeds from establishing, including grass seed. Do not apply pre-emergent if you plan to overseed. See the overseeding section below.

Killing crabgrass that’s already growing

Missed the pre-emergent window? You still have options, but they work best while the crabgrass is young. Once plants mature and set seed in late summer, control gets harder and you’re really just preventing next year’s crop.

Post-emergent herbicides

• Quinclorac: The most common and effective selective post-emergent for crabgrass. It targets crabgrass while leaving most cool-season turf grasses unharmed. Works best on young plants with 1 to 4 leaves; add a surfactant for better uptake on larger plants.
• Other actives: Products containing fenoxaprop or dithiopyr (which has both pre- and early post-emergent activity) are also widely sold.
• Read the label: Always confirm your turf type is listed as safe. A dedicated crabgrass killer applied in early summer beats a blanket weed-and-feed.
• Avoid spraying in extreme heat (over about 85 degrees F) to prevent stressing your lawn.

For a comparison of selective and non-selective formulas, our roundup of the best weed killers breaks down which products suit which jobs.

Hand-pulling

• For a few scattered clumps, hand-pulling is fast, free, and chemical-free.
• Pull when the soil is moist so the whole root crown comes up. Young plants slide out easily; mature ones need a weeding tool.
• Pull before seed heads form. A single crabgrass plant can produce thousands of seeds, so removing it early prevents next year’s invasion.
• Fill the resulting bare spot with grass seed (outside the pre-emergent window) so crabgrass can’t simply reclaim it.

The best long-term fix: a thick, healthy lawn

Herbicides treat the symptom. A dense, vigorous lawn treats the cause. When turf is thick enough to shade the soil, crabgrass seeds never get the sunlight they need to germinate. This is the most reliable, lowest-cost crabgrass control there is, and it pays off in a better-looking lawn overall.

Mow high

• Set your mower to the high end for your grass type, generally 3 to 4 inches for cool-season lawns.
• Taller grass shades the soil surface, blocking the sunlight crabgrass seeds need, and encourages deeper, more drought-resistant roots.
• Follow the one-third rule: never remove more than a third of the blade height in a single mowing.
• Keep mower blades sharp; ragged cuts stress the lawn and open gaps.

Fertilize and water properly

• Feed your lawn on a schedule suited to your grass and region so it stays dense enough to outcompete weeds. Our lawn fertilizer schedule shows when and how much to apply.
• Water deeply and infrequently, about 1 inch per week including rain, to promote deep roots rather than the shallow, surface-moist conditions crabgrass loves.

Overseed bare and thin spots

• Bare soil is crabgrass habitat. Overseeding thickens the turf so there’s no open ground for it to colonize.
• The catch: pre-emergent herbicides also block your new grass seed from establishing. Pick one strategy per area each season.
• The cleanest approach is to overseed cool-season lawns in early fall, when crabgrass is dying off anyway, then apply pre-emergent the following spring once the new grass is established.
• If you must overseed in spring, look for a pre-emergent labeled as safe to use with new seedings (such as siduron), or simply skip pre-emergent in that area for the season.

A season-by-season crabgrass plan

Put it all together and crabgrass control becomes a simple yearly rhythm rather than a midsummer panic.

Early spring

• Watch soil temperatures and your local forsythia.
• Apply pre-emergent before soil hits 55 degrees F, then water it in.
• Do not overseed treated areas this season.

Late spring to early summer

• Begin mowing high and keep it there all season.
• Spot-treat any escaped crabgrass with a post-emergent while plants are young, or hand-pull small clumps.
• Apply a second split pre-emergent if you’re in a long, hot climate.

Midsummer

• Continue mowing high and watering deeply but infrequently.
• Pull or treat any remaining plants before seed heads mature.
• Avoid herbicide applications during extreme heat.

Fall

• Crabgrass dies with the first frost. This is prime time to overseed thin spots and repair bare areas.
• Fertilize cool-season lawns to build density going into next spring.
• A thick fall lawn is your best defense against next year’s crabgrass.

A weed-free lawn is the foundation of a usable yard. For the bigger picture on patios, planting beds, and pulling it all together, visit our outdoor living guide.

Frequently asked questions