Crabgrass is an annual grass that dies at first frost and returns from seed every spring. Control is mostly about timing: pre-emergent products must go down before the soil reaches about 55°F, and a thick lawn mowed tall shades the seeds that remain. Once crabgrass is up, most pre-emergents no longer work.
How do you identify crabgrass?
University of Minnesota Extension says the common lawn species are large crabgrass (Digitaria sanguinalis), which can reach 3 feet, and smooth crabgrass (D. ischaemum), up to 1 foot. Both are annual warm-season grasses with light green blades 1 to 6 inches long, creeping stems that can root at the nodes, and fibrous roots. Older leaves and sheaths turn reddish-purple, and patches in a lawn look light green or yellowish.
What is its life cycle?
Minnesota says seeds germinate from early to late spring once the soil warms, plants grow through summer and form seedheads as days shorten, then drop seed and die by the first frost. It reports up to 150,000 seeds per plant in a season, so stopping seed set matters. North Dakota State says seeds keep germinating through summer but most sprout when soil is 60 to 70°F.
When should you apply a pre-emergent?
| Source | Germination trigger | Advice |
|---|---|---|
| University of Minnesota | Soil about 55°F | Apply in spring before soil reaches about 55°F; early or late application can dissipate or move off target |
| North Dakota State | Average soil at 55°F for 3 to 5 days, measured 2 inches deep | Apply before the soil averages 55°F; water in about 1/2 inch after granular products |
| Nebraska Extension (Buffalo County) | Soil at 55°F or above for several days, measured 4 inches deep | Nebraska’s typical window is about April 15 to May 1; a second treatment around midsummer may be needed |
The sources agree on 55°F but measure it at different depths (2 inches versus 4 inches), so use a local soil-temperature reading and treat a few days early rather than late. Pre-emergents do not kill seeds; they stop seedlings as they germinate and do not control plants already up. Do not use standard crabgrass preventers on newly seeded lawns; North Dakota State suggests siduron or a starter fertilizer with mesotrione for new seedings.
What cultural practices help?
- Dense, healthy turf is the most effective way to reduce crabgrass (Minnesota).
- Mow at least 3 inches high to shade the soil (Minnesota); Oregon State cites about 3 to 4 inches.
- Water deeply, since shallow, frequent watering encourages shallow roots that favor weeds (Oregon State).
- In beds, a 2 to 3 inch mulch layer blocks light (Oregon State).
- Hand-pull small infestations when soil is moist, and dispose of plants so they cannot reseed (Oregon State).
What about killing crabgrass that is already growing?
Minnesota says post-emergent herbicides work best on young plants and that treatment after early July in Minnesota is ineffective. Named options include mesotrione, quinclorac, topramezone and dithiopyr, each with its own growth-stage window on the label. North Dakota State adds that dithiopyr can control seedlings at the one- to three-leaf stage if the pre-emergent window was missed. Avoid non-selective herbicides on lawns, and follow the label.
Plan feeding with the fertilizer calculator and browse the weed library.
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Frequently asked questions
What temperature does crabgrass germinate at?
All three sources cite about 55°F soil temperature, held for several days, though they measure it at different depths.
Can I put pre-emergent on a new lawn?
Not a standard one, because it also stops grass seedlings; use a product labeled for new seedings.
Does crabgrass come back every year?
It is an annual, so it returns only from seed, which is why preventing seed set and germination works.
Reviewed November 2026. Sources: University of Minnesota Extension: Crabgrass; NDSU Extension: Prevent crabgrass this spring; Nebraska Extension, Buffalo County: Crabgrass; Oregon State Extension: How do I get rid of crabgrass?
