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Crabgrass: getting the pre-emergent timing right

Crabgrass is the first summer weed to germinate in Midlands lawns. It is an annual, and a pre-emergent put down on time, watered in and renewed on schedule controls it. This page covers the timing, because timing is where most do-it-yourself crabgrass control goes wrong.

What does crabgrass look like?

Crabgrass grows in low, spreading tufts with hairy stems and broader leaves than your lawn grass. In summer it sends up seedheads with two to nine finger-like branches. Clemson lists several species in South Carolina, including large, smooth and southern crabgrass.

When should crabgrass pre-emergent go down in the Midlands?

Clemson's pages give dates from mid-February to March 1 for central South Carolina, and several also give warmth-based triggers. Clemson says crabgrass begins germinating when soil reaches 57 degrees, and UGA says to apply pre-emergent before soil reaches 55 degrees. A run of warm February days can start it early. Clemson also notes the false springs we get in South Carolina make timing difficult.

Why does one spring application sometimes fail?

• It wears off. A pre-emergent lasts roughly 6 to 12 weeks, and crabgrass keeps germinating after the first flush. Clemson's guidance for season-long control is a second application eight or nine weeks after the first.
• It wasn't watered in. Most pre-emergents need irrigation or rain right after application. Clemson's pages call for a quarter to half an inch.
• It went down late. If the soil warmed before the application, the first flush of crabgrass is already up.
• The barrier got broken. UGA notes that disturbing treated soil reduces a pre-emergent's effect, and Clemson's calendars say to hold aeration until just before the next pre-emergent application.
• The lawn is thin. Clemson calls crabgrass a sign the grass is too thin, mowed too low, or kept too wet. A thick lawn is the best defense.

Can I kill crabgrass once it's up?

Clemson notes crabgrass is very difficult to control with most herbicides once it has formed a few tillers or branches. Young plants are easier, and some products labelled for crabgrass work only before tillering. On centipede and St. Augustine, Clemson warns against post-emergent products during green-up or above 90 degrees.

How does Spring Green handle crabgrass?

Our lawn care program puts down summer pre-emergent in two rounds, the first between February and April and the second in April or May, and every visit includes post-emergent weed control. The schedule shifts by up to a month with the weather. Because thin turf lets crabgrass in, the soil test and fertility program are part of the fix.

Last updated 2026-09-25. Spring Green is owned by Stockton Wells.