When should you
apply pre-emergent?
Enter your ZIP code. We'll tell you if it's time — based on real weather station data and Growing Degree Days.
Built on NOAA GHCN-Daily observations covering 33,000+ US ZIP codes, recomputed daily.
Data details
Worth buying for this timing
Best fit for this result
Some links are sponsored. We may earn a commission, but your ZIP result determines which product types we show.
Full-season preventive
Prodiamine
Prodiamine 65 WDG
Best fit: You are approaching or inside the pre-emergent window and want the longest barrier from one application.
This is the value play: one correctly timed barrier can protect the season instead of chasing weeds later.
Cannot kill already-germinated weeds
Late-window preventive
Dithiopyr
Dimension 2EW
Best fit: Your timing is tight and you want the common pre-emergent with limited early crabgrass activity.
Helps avoid buying a long-residual product after the window has narrowed.
Shorter residual than Prodiamine
Not a rescue treatment for mature or widespread visible crabgrass.
Granular easy application
Pendimethalin
Scotts Halts / Pendulum
Best fit: You want a spreader-ready option instead of mixing and spraying a liquid product.
Trades pro-style mixing for a simpler job you can finish while timing still matters.
Needs watering in within 24 hours; stains concrete
How Growing Degree Days Work
Growing Degree Days (GDD) measure accumulated warmth in the air-temperature record since January 1. Each day the average temperature exceeds 50°F, the difference is added to your running total. When that total reaches 150–200 GDD, crabgrass and other summer annual weeds are about to germinate. That is the window for pre-emergent herbicide.
Why Pre-Emergent Timing Matters
Pre-emergent herbicides form a chemical barrier in the top layer of soil that stops weed seeds before they sprout. Apply too early and the barrier breaks down before peak germination. Apply too late and the weeds are already growing. GDD tracking removes the guesswork by tying your application to actual soil temperature rather than calendar dates, which vary year to year.
This tracker pulls daily temperature observations from your nearest NOAA weather station and calculates GDD for over 33,000 US ZIP codes.
Pre-Emergent Guides by State
Application timing varies across the country. Southern states may need pre-emergent as early as January, while northern states often wait until April or May. Find your state for local timing and grass type recommendations.