Mow your lawn to the recommended height for your grass type. Make sure the lawn is dry before applying the preventer.
The soil temperature should be around 55°F (13°C) for a few consecutive days. This is typically when the forsythia flowers start to bloom.
Select a pre-emergent herbicide labeled for crabgrass prevention. Products may contain ingredients like pendimethalin, prodiamine, or dithiopyr.
If you have already seeded your lawn, wait until the new grass is well-established before applying crabgrass preventer, as it can inhibit the growth of grass seedlings