When to Apply Pre-Emergent, State by State

Cool-season lawns: why then

Crabgrass germinates when soil at 1–2″ depth holds around 55°F for several days — typically the weeks right around the average last frost, when forsythia is blooming. Pre-emergent must be down and watered in *before* germination; a week late and the first flush is already up. Frost dates are a serviceable proxy, but a $15 soil thermometer (or your state extension’s soil temperature map) is the honest trigger.

Warm-season lawns: why then

Southern soils cross the crabgrass-germination threshold (~55°F at soil level) early — often by late February along the Gulf. The window here runs the three weeks up to the average last frost, and earlier beats later: pre-emergent that goes down after soil warms is wasted. Skip pre-emergent anywhere you plan to seed this spring; it can’t tell crabgrass seed from grass seed.