Loading pre-emergent timing
Crabgrass preventer and fall poa annua timing based on current modeled soil temperature estimates for this location.
Modeled estimate
Soil is well above the crabgrass germination threshold, so a spring pre-emergent application no longer helps. Switch to a post-emergent strategy for visible weeds, and plan for the fall poa annua application described below.
Modeled for this location because a current station reading was unavailable. Confirm with a soil thermometer before applying.
Crabgrass and most summer annual weeds begin germinating when the 2-inch soil temperature sustains 55°F for 3–5 consecutive days. Pre-emergent herbicides, the products sold at retail as crabgrass preventer, create a chemical barrier at the soil surface that prevents weed seeds from sprouting. The barrier must be in place before germination begins.
Pre-emergent has a second season. Poa annua (annual bluegrass) and other winter annual weeds germinate in fall as the 2-inch soil temperature drops back through 70°F after the summer peak, with most germination in the 65–70°F falling range. A fall application ahead of that crossing stops poa annua the same way a spring application stops crabgrass.
The J B P H H lawn care schedule tracks this window live against daily station readings. For products, rates, and the germination research behind the thresholds, see the fall pre-emergent timing guide.
Look for products containing prodiamine, dithiopyr, or pendimethalin. Dithiopyr has mild post-emergent properties and can suppress very young crabgrass (1–2 leaf stage) even if applied slightly late. Weed-and-feed products that pair fertilizer with a pre-emergent follow the same soil-temperature window: the preventer half only works if it is down before the 55°F crossing.
Full lawn care schedule for J B P H H →
Spring pre-emergent herbicide guide →
Enter your city or ZIP code to see current 2-inch soil temperatures and find out whether the crabgrass prevention window is still open.