Since Kansas crabgrass typically sprouts in early May, mid-April is a good deadline for applying crabgrass preventer.

“Because traditional preventers are just what their name implies, they have to be applied before crabgrass germinates. But many become fairly ineffective after about 60 days, so you can’t apply them too early, either,” said Ward Upham, horticulturist with Kansas State University Research and Extension.

Given the state’s area weather differences, some Kansans time their application for when local Eastern redbud trees are near full-bloom, Upham added. That generally ranges from April 1 in southeast Kansas to May 1 in the northwest.

“With traditional products, you’re also likely to need a follow-up application about eight weeks later,” he said. “That will control the last seeds to germinate.”

The only exceptions to these rules are two preventers often sold under the trade names Barricade (prodiamine) and Dimension (dithiopyr). Both are easiest to find in combination with fertilizer. Both are effective for much longer — with Barricade applied in either fall or spring for spring crabgrass control.

Dimension can go down as early as March 1 or even after April 15. It’s the only control that actually can kill crabgrass seedling plants, too, Upham said.

“However, if you can’t find Dimension or dithiopyr outside a high-nitrogen fertilizer mix, it will not only discourage crabgrass but also encourage lush top growth in your lawn,” he said.