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
Overseeding-compatible option
Mesotrione
Tenacity / Torocity
Best fit: You are overseeding a compatible cool-season lawn during the fall weed-prevention window.
Preserves the overseeding plan while providing a seeding-compatible alternative to standard pre-emergents.
Turf-species restrictions and application rates vary; follow the product label
Sun & Shade Seed Mix
Sun & Shade Seed Mix
Scotts Turf Builder Sun & Shade Mix / Jonathan Green Black Beauty
Best fit: Northern lawns with mixed sun and shade; general-purpose overseeding
Check the label, coverage area, and current price before you buy.
Mixed-species blends establish unevenly if the seedbed is not kept moist
Tall Fescue Seed + Starter Food
Tall Fescue Seed + Starter Food
Scotts Turf Builder Rapid Grass
Best fit: Transition-zone and southern cool-season lawns; heat and drought tolerance
Check the label, coverage area, and current price before you buy.
Coarser blade than bluegrass; will not spread to fill bare spots on its own
Timing check
Soil Thermometer
Urban Worm 5-in stem / Taylor 4-in stem
Best fit: You want to confirm this estimate in your own yard before you apply.
This tracker models soil temperature from NOAA air observations, so expect about ±5°F against a reading taken at 2 inches in your own soil.
Read the same spot at the same time of day; one warm afternoon is not a trend
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.
- 0–100 GDD Too early. Soil is still cold.
- 100–150 GDD Getting close. Buy your product and plan your application.
- 150–200 GDD Apply now. Ideal pre-emergent window.
- 200+ GDD Window closing. Weed seeds are germinating.
Fall Pre-Emergent Timing for Poa Annua
Fall timing runs in reverse: watch estimated soil temperature cool through about 70°F with a downward trend. As its own display heuristic, the tracker labels temperatures above 70°F through 75°F as Getting Close only while they are cooling; above 75°F, it shows Too Warm. Above 55°F through 70°F while cooling, apply for Poa annua, henbit, and chickweed. At or below 55°F, the tracker treats the preventive window as passed because UGA Extension advises applying before soil cools to 55°F, when winter weeds begin germinating.
When timing still makes sense, the fall card recommends prodiamine or dithiopyr, which Clemson rates for good-to-excellent annual bluegrass control. It recommends no pre-emergent after the window has passed, because pre-emergents offer little benefit after annual bluegrass is established. If you are overseeding, select that option to replace the standard products with mesotrione, a seeding-compatible alternative for labeled turf species. Read the complete fall pre-emergent guide.
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.