How to Kill Crabgrass (and Prevent It Forever)
A practical guide to identifying, treating, and preventing crabgrass, with pre-emergent timing and post-emergent options that actually work.
Crabgrass is the number one weed in American lawns. It thrives where turf is thin, loves hot soil, and spreads fast once it takes hold. Here is what to do.
How to spot it
- Lime green blades, wider and flatter than lawn grass.
- Low-growing, spreading habit. Looks like a spider laying flat.
- Pops up in summer, especially along driveways, sidewalks, and thin edges.
Pre-emergent is the real answer
Crabgrass seed germinates when soil temperature hits 55 degrees Fahrenheit for three to five days. A pre-emergent herbicide applied before that point prevents 90 percent of germination.
- Early-season windows vary by region. Atlanta is February. St. Louis is late March. Minneapolis is late April.
- Split applications (two lighter passes four to six weeks apart) outperform a single heavy dose.
- Do not apply pre-emergent if you just overseeded. It kills your new grass too.
Post-emergent options
If crabgrass is already visible, pre-emergent is useless. Use a selective post-emergent herbicide labeled for crabgrass. Common active ingredient: quinclorac.
Spot-treat small patches. Full-lawn applications stress turf and are usually unnecessary.
The long game
Thin turf is what lets crabgrass win. Fix the cause:
- Mow tall. See how often should you mow.
- Aerate in fall and overseed thin areas.
- Fertilize on a proper schedule.
Related reading
- Spring lawn care checklist
- Best grass types by climate
- Weed control service
- Lawn fertilization service
Want a pro to handle timing and application? Book weed control in your city.