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Crabgrass
One of the most common and frustrating lawn weeds in the country - a fast, heat-loving annual grass that colonizes thin turf and bare soil every summer. This entry is about identifying and controlling it, not growing it.
Safety notes Crabgrass is not toxic - it's a nuisance weed, not a hazard. Its seed is actually edible and was historically harvested as a minor grain (a relative of the cultivated grain fonio), so there's no danger from having it in the yard. The real 'safety' issue is indirect: many people reach for herbicides to control it, so follow all product label directions carefully and consider non-chemical control first. As a plant to handle, it's harmless.
Overview
Crabgrass (Digitaria sanguinalis) is the weed most homeowners are actually thinking of when they complain about their lawn. It's a warm-season annual grass that germinates as the soil heats in spring, then sprawls into wide, low, star-shaped ('crab-legged') mats that thrive in the heat of summer - exactly when cool-season lawn grasses thin out and struggle. It moves into bare soil, thin turf, and hot edges along driveways and sidewalks, and a single plant can produce thousands of long-lived seeds, so it comes back year after year.
Unlike the other plants in this catalog, you're almost certainly here to get rid of crabgrass, not to grow it - so this entry is built around identifying and controlling it. (For the record, it's not toxic, and its seed is even edible - a relative of the cultivated grain fonio was historically gathered from crabgrass - but as a yard plant it's simply a weed.) The good news: understanding its warm-season, sun-and-bare-soil biology is the key to beating it, mostly by timing and by growing a thick, healthy lawn.
Quick facts
For identification. Not a growing guide.
- Height
- 12 inRange: 4–24 in
- Spread
- 18 inRange: 6–36 in
- Cold
- Killed by frostdamaged below 32°F
- Heat
- Struggles above 110°F
- Life cycle
- Annual
- Self-sows
- Yes. Never let it set seed.
- Habitat
- Full sun, well-drained soil
Through the year
A field guide through time
Explore the stages to recognize this plant throughout its life.
Stage 1 of 4 · The growing sequence
Spring germination (control window)
Day 0 to 14 from sowing
Know this stage
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The key control moment: prevent germination
Crabgrass seed germinates as soil warms to about 55-60F in spring (roughly when soil-temperature indicators like forsythia finish blooming or lilacs bloom). This is when pre-emergent control works - applied BEFORE germination, it stops the seedlings; applied after, it's useless. Timing is everything.
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Recognize the seedlings - and rule out goosegrass
Seedlings look like a small, wider-bladed grass in thin or bare spots, especially along hot edges (driveways, sidewalks). Check it really is crabgrass: goosegrass (Eleusine indica) sprawls the same way but has a flattened, silvery-white center at the crown (the 'silver dollar') and stems that do NOT root at the nodes, while crabgrass roots readily at the nodes and has no white crown. Goosegrass also germinates weeks later, in hotter soil, so this timing misses it.
Stages can overlap; weather, variety, and growing conditions change the pace.
Hazards
Seed Set (the multi-year problem)Severity High DisordernowSeason: Jul–OctFinger-like seed heads forming from mid-summer on - the point at which each plant is about to reload the soil seed bank.
Finger-like seed heads forming from mid-summer on - the point at which each plant is about to reload the soil seed bank.
Pull, dig, or mow off plants before seed ripens; persistent seed-set prevention each year is what finally reduces crabgrass.
Remove or kill plants before the seed heads mature; combine with dense turf and correct pre-emergent timing to shrink the seed bank over years.
The reason crabgrass persists: each plant can drop thousands of seeds that survive years in the soil, so allowing plants to seed guarantees future infestations - preventing seed set is the key to long-term control.
Dense Turf & Shade (its main control)Severity High DisorderSeason: Apr–JulFor the gardener: thin, short-mowed, bare, or compacted turf is where crabgrass wins - those are the spots to thicken.
For the gardener: thin, short-mowed, bare, or compacted turf is where crabgrass wins - those are the spots to thicken.
Thicken and overseed weak turf, mow high, and improve soil - a dense lawn prevents most crabgrass without herbicides.
Grow a dense lawn: mow cool-season grass high (3-4 in), overseed thin areas, fix bare and compacted spots, and keep hot edges thick or mulched.
From the weed's perspective, a thick, tall, healthy lawn is its greatest enemy: crabgrass needs full sun and bare or thin soil to germinate and establish, and dense shading turf denies it both - the single most effective, chemical-free control.
Pre-Emergent Control WindowSeverity Medium DisorderSeason: Mar–MaySoil warming to ~55-60F, and the natural cue of forsythia finishing / lilacs blooming - the germination trigger.
This forsythia/lilac timing is for crabgrass only. Goosegrass (Eleusine indica), the weed most often misidentified as crabgrass, germinates several weeks later at ~60-65F+ and shrugs off several common crabgrass pre-emergents - if a 'crabgrass' problem survives correctly timed control, check the crown for goosegrass's flattened silvery-white center.
Soil warming to ~55-60F, and the natural cue of forsythia finishing / lilacs blooming - the germination trigger.
If the window is missed, switch to post-emergent control of young plants and hand-removal, and plan pre-emergent timing better next spring.
Apply any pre-emergent BEFORE germination (early-to-mid spring by the soil-temperature cue), or use non-chemical prevention (thick lawn, early hand-removal).
The narrow spring window when crabgrass seed germinates is when pre-emergent control works - and missing it (applying too late, after germination) is the most common reason control fails.
Grower tips
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