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Frost dates for Thornton, Colorado

In a typical year, Thornton’s last spring frost lands around May 2 and the first fall frost around Oct 11, a growing season of about 162 days. These are odds drawn from 30-year NOAA climate normals, not a promise. USDA zone 6a.

Right now the typical frost season has arrived; planting waits for spring.

Last spring frost and first fall frost odds for Thornton, Colorado
OddsLast spring frostFirst fall frost
10 percentApr 18Sep 26
50 percentMay 2Oct 11
90 percentMay 14Oct 24

A 10 percent year is an early year, a 90 percent year a late one. Frost-sensitive planting usually waits for the 90 percent side of the last-frost band.

Soil in Thornton is typically around 50°F at 4 inches this time of year, estimated from the last two weeks of normal air temperatures.

See what is plantable in your ZIP with the what-to-plant lookup.

Common questions

When is the last frost in Thornton, Colorado?

Thornton’s last spring frost falls around May 2 in a typical year. One year in ten it is done by April 18, and one year in ten frost holds on until May 14. Frost-sensitive planting usually waits for the late side of that band.

When is the first fall frost in Thornton?

The first fall frost arrives around October 11 in a typical year, as early as September 26 in an early year and as late as October 24 in a late one.

How long is the growing season in Thornton?

About 162 days, counted between the typical last spring frost and the typical first fall frost.

What USDA zone is Thornton in?

Thornton is in USDA hardiness zone 6a under the 2023 USDA Plant Hardiness Zone Map.

Dates come from 30-year NOAA climate normals for the nearest reporting station. They describe odds, not a forecast.

Nearby cities

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