The research has shown that putting the preventers down in late March is not much different than putting it down around April 10. So, spread that preventer when you can, but before the crabgrass germinates.

By Jef Burbrink
Extension Educator, Ad & Natural Resources, Purdue Extension – LaGrange County

Jeff Burbrink

LAGRANGE COUNTY — Every year in March, Indiana residents begin asking when the best time to apply crabgrass preventers to their lawns. For some reason, people have it stuck in their minds there is a perfect date to do this task.

The important thing to know is that the preventers need to be in place before the crabgrass sprouts. Once sprouted, the preventers do no good for you. Crabgrass germinates when the soil temperatures are 50-57 degrees for three or more consecutive days, and there is adequate soil moisture. Germination in northern Indiana is around the end of April in our region, plus or minus 10 days. That’s a wide range of dates. Since temperature is important, sunny areas of your lawn may germinate quicker than shady areas or northern facing slopes.

Is there harm in putting the crabgrass on too early? The research has shown that putting the preventers down in late March is not much different than putting it down around April 10. So, spread that preventer when you can, but before the crabgrass germinates. There was even some research done years ago that showed there was some modest crabgrass control when the products were applied in November or December.

If you still feel you need the most optimum time to put down the preventer, visit Michigan State’s GDD tracker at gddtracker.msu.edu/ On the side menu next to the map, click on Crabgrass PRE. The green area on the map indicates the optimum timing. Again, better early than late!

Purdue has a publication on crabgrass prevention at turf.purdue.edu/extpub/control-of-crabgrass-in-homelawns.

One other thought: the research on turfgrass has shown that it is best to wait until later in the season to apply nitrogen fertilizer. Applying fertilizer too early tends to cause the grass to break its dormancy too early, and has been proven to encourage certain turf diseases, which show themselves later in the season. Many crabgrass preventers contain nitrogen.

I tell those people who are really into lawncare to find a crabgrass preventer that is no or low nitrogen, apply that around March 30-April 10, then wait until mid-May to apply your first dose of fertilizer. More information on lawn fertilizer at turf.purdue.edu/extpub/fertilizing-established-lawns.