Quick answer
Crabgrass is much easier to prevent than kill. Apply a pre-emergent in early spring, before soil warms enough for seeds to sprout, and keep the lawn thick so there's no bare ground for weeds.
Timing the Pre-Emergent
Pre-emergent forms a barrier that stops seeds from sprouting. Applied after crabgrass is already up, it does little. A second, follow-up application is common to extend protection.
Lawn Habits That Help
- Avoid scalping, which opens up bare soil
- Water deeply and less often
- Fix thin areas so weeds can't take hold
- Keep edges along concrete trimmed and healthy
Watch Out When Seeding
Most pre-emergents also stop grass seed from sprouting. If you plan to seed, time it around the product's label.