When is the best time to prevent crabgrass?

Asked April 9, 2014, 5:38 PM EDT

I just sowed new seed. I am worried about crabgrass. I read not to fertilize until three lawn cuttings. Will there still be time to use a pre-emergent crabgrass preventer, or will the crabgrass already be established?

Philadelphia County Pennsylvania

1 Response

Pre-emergent crabgrass herbicides work by preventing all seeds from taking root, so now would not be the time to apply crabgrass control because it would negate the new seed recently planted.

Our recommendation would be to continue to build a strong, thick turf through the balance of the year and attempt spot control of any crabgrass that appears during the summer to reduce self seeding of crabgrass.

Fall is typically the best time to reseed or overseed which you might consider later this year to continue to build a strong, thick turf and crowd out weeds. Next spring you can apply corn gluten to prevent crabgrass and other annual weeds.

Please note that timing of the crabgrass control is also critical. The ground temperature needs to be 55° to 58°F in the top 1 inch of soil for 4 to 5 consecutive days. This typically occurs between mid-March and mid-April in your area. The application then needs to be watered in, and then you need a couple of days of dry weather to prevent the crabgrass and other weeds from establishing a root system.

You may need to repeat crabgrass control application for a few years to increase its effectiveness.