Why soil temperature decides when grass goes dormant
Grass doesn't read the calendar. Warm-season grass slows down and shuts off as the soil around its roots cools, and it wakes up again when that soil warms. That's why the same grass goes dormant on different dates in different towns.
Air temperature swings from day to night, but soil changes slowly. A 7-day average of soil temperature tracks what the roots are actually feeling, which is why this tool smooths 10 years of daily readings before it looks for your dates.
Want today's reading instead of the typical year? Check your current soil temperature and compare it against the thresholds above.
What a warm-season lawn does from fall to spring
- Entering dormancy: once average soil drops below 60°F, warm-season grass is shutting down for winter. Skip nitrogen and seeding, and keep mowing at your normal height until growth stops.
- Goes dormant: as average soil falls to about 50°F, bermuda, zoysia, St. Augustine, centipede and bahia turn tan. NC State's Grady Miller puts the brown-out point there, and the first hard frost finishes it.
- Stays dormant: the grass is alive but resting. Keep heavy traffic off frosted turf and don't feed it.
- Greens up: when soil reaches about 65°F at 4 inches, the trigger UGA uses, new green pushes up from the crowns. That's also when fertilizer goes back down.
Brown in the middle of the growing season is a different story. Here's how to tell dead grass from dormant grass, with the tug test and the other checks that settle it.
What cool-season grass does in winter and summer
Tall fescue, Kentucky bluegrass, perennial ryegrass and fine fescue run on the opposite schedule. They slow down near freezing and hold most of their color through winter, with growth pausing once soil drops below about 40°F.
Summer is the harder season for them. When soil runs above 80°F, these grasses can go dormant to ride out heat and drought. The tool counts how many days a typical year runs that hot at your ZIP, and zero is a common answer in the North.
How this tool works out your dates
- Soil data: 10-year daily averages from the Open-Meteo soil model, built on ECMWF ERA5-Land reanalysis, for the 0-7 cm layer (about 2 to 3 inches deep) at your ZIP.
- Smoothing: each day is averaged with the three days before and after it, wrapping across New Year's, so one odd day can't move your date.
- Fall dates: starting August 1, the tool finds the first day the smoothed soil falls below each fall threshold.
- Spring date: from your dormant date it finds the first day the soil gets back to the green-up threshold, which usually falls in the next calendar year.
- Edge cases: where average soil never drops below 50°F or never reaches 65°F, the tool says so instead of showing a made-up date.
For the full grass-by-grass rundown, read when does grass go dormant, the guide these thresholds come from.