Weed Control
Crabgrass: How to Identify and Kill It in a Lawn
Quick answer
Crabgrass is a summer annual grass, so the control that works is a pre-emergent such as prodiamine or dithiopyr applied before soil holds 55 F at 2 inches, backed by mowing at 3 to 4 inches. For plants already up, quinclorac is the standard post-emergent.
Crabgrass is an annual. Every plant in your lawn this year grew from seed this year, and every plant dies at the first hard frost. That single fact decides the whole strategy: you are fighting seed germination in spring, not a root system that lives through winter. A pre-emergent barrier put down at the right soil temperature does more than any spray you make later.
The second fact is that crabgrass seed needs light and warm bare soil. It germinates in the thin, scalped, sun-baked strips along driveways and sidewalks, not in dense turf mowed at 3.5 inches. Work out how much product you need with the lawn size calculator, then plan the fall overseeding that closes the gaps with the grass seed calculator.
On this page
How do I identify crabgrass?
| Trait | Crabgrass |
|---|---|
| Weed type | Grassy weed, not a broadleaf and not a sedge |
| Life cycle | Summer annual; dies at the first hard frost, returns from seed |
| Season | Warm season; germinates in spring, peaks in summer heat |
| How it spreads | Seed only, though sprawling stems root at the nodes where they touch soil |
| Leaf | Wide, coarse, light yellow-green blades, much paler than the turf around them |
| Growth habit | Flat rosette of stems radiating from one center, like a star or crab pressed to the ground |
| Seedhead | Two to six finger-like spikes at the top of a stalk, spread like a bird foot |
| Roots | Shallow and fibrous; a mature clump pulls up with a shovel of soil attached |
| Where it shows first | Driveway and sidewalk edges, south-facing strips, thin sunny spots |
| What it says about the lawn | Mowing too low, thin turf, compacted or drought-stressed soil, bare edges |
Goosegrass looks similar but has a silvery-white flattened center and a zipper-pattern seedhead. Check /weeds/goosegrass before you buy a product, because the two do not respond to the same post-emergents.
Why do I have so much crabgrass?
Crabgrass is a light-loving opportunist. Its seed sits in the top half inch of soil and germinates when that layer warms and gets sunlight, so anything that thins the canopy invites it. The three usual causes are mowing too short, a lawn that went dormant and thin in summer drought, and compacted strips that turf cannot hold.
Raising the mowing height is the cheapest control you own. A cool-season lawn held at 3.5 to 4 inches shades the soil surface enough to cut germination sharply, and the same mower that scalps at 2 inches does the opposite. Check your grass against the mowing height chart, since tall fescue wants 3 to 4 inches while bermudagrass is cut far lower and needs a different plan.
Edges deserve special attention. Pavement stores heat, so soil within a foot of concrete hits 55 F days before the middle of the lawn does, which is exactly why the first crabgrass of the year appears there.
What kills crabgrass without killing grass?
Pre-emergent herbicides stop seedlings as they germinate, and post-emergents kill plants you can already see. They are different jobs with different chemistry, which is covered in pre-emergent vs post-emergent. Timing is set by soil temperature, not by a date on a calendar.
| Method | When | What it involves |
|---|---|---|
| Raise the mowing height | Every mowing, all season | Hold a cool-season lawn at 3.5 to 4 in. Shade on the soil is the control that costs nothing and never fails a label check. |
| Fix the thin spots | Late summer to early fall, soil 50 to 65 F | Overseed so there is no bare soil for next year seed to land on. See how to overseed a lawn. |
| Water deeply, less often | Through summer | About 1 inch a week in one or two soakings grows deeper turf roots. Daily light sprinkling favors shallow-rooted crabgrass. |
| Hand pulling | Spring and early summer, while plants are small | Practical for a few dozen plants. Pull before the seedhead forms, because one plant can shed thousands of seeds. |
| Pre-emergent herbicide | Before soil holds 55 F at 2 in for several days | Prodiamine or dithiopyr, granular or sprayed, watered in per the label. This is the main control. |
| Split pre-emergent application | Second half of the label window | Long summers break the barrier down early. Many labels allow a second application to carry control later. |
| Post-emergent for plants already up | When crabgrass is young, or after it has more than 4 tillers | Quinclorac is the standard choice. Mesotrione is an option on cool-season lawns and bleaches treated plants white. |
| Do nothing and wait | Late in the season | Crabgrass dies at the first hard frost. Late spraying kills a plant that had weeks left and leaves a bare hole anyway. |
Measure soil temperature 2 inches deep in the morning with a soil thermometer. Do not apply a standard pre-emergent in the same season you plan to seed, because prodiamine and dithiopyr stop grass seed as well as weed seed.
Which crabgrass products do what?
For prevention with a spreader, Scotts Halts Crabgrass and Grassy Weed Preventer, 20.12 lb is a straight pre-emergent with no fertilizer, so you can time it to soil temperature instead of a feeding. Lesco 0-0-7 with 0.43% Stonewall Pre-Emergent, 50 lb does the same job on a potassium carrier and covers 12,500 sq ft. If you own a sprayer, Quali-Pro Prodiamine 65 WDG Pre-Emergent Herbicide, 5 lb is the generic prodiamine that many people use for years out of one bottle.
For crabgrass already up, BASF Drive XLR8 Crabgrass Killer Concentrate, 64 oz is a quinclorac post-emergent labeled for crabgrass and foxtail on warm and cool-season turf. Quinclorac has a known weak spot: it is least effective on plants in the middle of tillering, roughly the two to four tiller stage, so treat seedlings early or wait until clumps are mature. Syngenta Tenacity Turf Herbicide, 8 oz is mesotrione, which has both pre and post activity on cool-season lawns and turns treated weeds white for a week or two before they die.
Roundup Weed and Grass Killer4 Concentrate, 1 gal is non-selective. It kills crabgrass and it kills the lawn grass it touches, so it belongs on driveway cracks and renovations, never as a spot spray in turf you intend to keep. Tiered picks are in the best crabgrass preventers.
What gear helps with crabgrass?
A spreader that lays an even barrier, a sprayer for spot work, and a mower that holds 4 inches without scalping. An uneven spreader pass is the most common reason a pre-emergent fails: crabgrass comes up in the stripes that got missed. Compare hopper types in drop vs broadcast spreaders.
Scotts Turf Builder EdgeGuard DLX Broadcast Spreader
$94.97A pre-calibrated push broadcast spreader that holds up to 15,000 sq ft of product, with an EdgeGuard shield that keeps granules off the driveway where they do nothing.
Best for: lawns up to about a third of an acre
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Chapin 16200 2-Gallon Pump Sprayer
$26.44A 2 gallon poly pump sprayer with an adjustable cone nozzle and in-tank filter, enough to treat clumps along a driveway without mixing a backpack full.
Best for: spot-treating crabgrass along edges
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EGO POWER+ LM2135SP 21 in. Select Cut Self-Propelled Mower Kit
$749.00A battery self-propelled mower with a 1 to 4 inch cutting height range, so a cool-season lawn can sit at the top notch through crabgrass season.
Best for: mowing high on lawns up to about half an acre
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Jonathan Green Black Beauty Ultra Grass Seed, 7 lb
$43.99A tall fescue, bluegrass and ryegrass mix rated for 1,400 sq ft new or 2,800 sq ft overseeded, for filling the thin strips where crabgrass starts.
Best for: fall overseeding of thin edges
Check price on AmazonHow we chose
We did not test these products in person. Picks are researched from manufacturer specifications and owner manuals, engine and safety certifications where they apply, warranty terms, public recall records, and the recurring themes in verified owner reviews. We favor established brands with large review counts and parts support, match each pick to a real yard size or task, and place it in the tier where its price and capability actually belong.
Frequently asked questions
When is it too late to apply crabgrass preventer?
Once crabgrass has germinated, a pre-emergent will not touch it, and germination starts when soil holds about 55 F at 2 inches for several consecutive days. If you already see wide light-green seedlings, switch to a post-emergent such as quinclorac and plan next year around a soil thermometer instead of a date. Many labels allow a second application later in the window to extend the barrier.
Can I put down crabgrass preventer and grass seed together?
Not with standard products. Prodiamine and dithiopyr stop grass seed exactly as they stop crabgrass seed, so an overseeding and a pre-emergent cancel each other out. Mesotrione is the common exception and some labels allow it at seeding on listed cool-season species. Read the label for the seeding interval, and in most lawns it is simpler to overseed in fall and apply pre-emergent in spring.
Does crabgrass come back every year?
The plants do not, but the seed does. Crabgrass is a summer annual that dies at the first hard frost, and every plant you see grew from seed in the soil. A single plant can produce thousands of seeds, and that seed bank stays viable for several years. That is why one good season of prevention helps but does not finish the job, and why thick turf matters more than any spray.
Will mowing high really stop crabgrass?
It will not eliminate it, but it is the single most effective cultural control. Crabgrass seed needs light at the soil surface to germinate, and turf held at 3.5 to 4 inches shades that surface. Lawns scalped at 2 inches give the seed exactly the light and warm bare soil it wants. Mowing high also grows deeper roots, which helps the turf outcompete crabgrass in summer.
Researched, not professional advice. This page is compiled from published specifications, manuals, labels and owner-review consensus, not hands-on testing. Follow the manufacturer's instructions and product label, and consult a qualified professional where safety, chemicals, fuel or structures are involved. As an Amazon Associate we earn from qualifying purchases.