Last frost date in Thornton, Colorado
May 2
Average last frost in spring. In an early year (1 in 10) it's over by April 18; in a late year (1 in 10) it comes after May 14.
October 11
Average first frost in fall. 1 year in 10 it comes by September 26.
Source: NOAA U.S. Climate Normals 1991–2020, station Northglenn (USC00055984), 4.1 miles from Thornton, elevation 5,407 ft. NOAA National Centers for Environmental Information. These are long-term averages, not a forecast.
This station is also the nearest one for Broomfield, Federal Heights, Lafayette, Northglenn and Westminster, so their frost dates are the same as Thornton's.
| Early year | Average | Late year | |
|---|---|---|---|
| Last frost in spring | Apr 18 | May 2 | May 14 |
| First frost in fall | Sept 26 | Oct 11 | Oct 24 |
Frost-free days in an average year: 160
| Chance in a year | Average last in spring | Average first in fall | |
|---|---|---|---|
| Light frost (36°F) | Every year | May 12 | Oct 1 |
| Frost (32°F) | Every year | May 2 | Oct 11 |
| Hard freeze (28°F) | Every year | Apr 20 | Oct 21 |
Nights at 32°F or colder in an average year: 149
What to plant now in Thornton
- Spring planting calendar for an average last frost around April 30 Thornton: May 2
- Fall planting calendar for an average first frost around October 10 Thornton: October 11
Planting dates: USDA Home and Garden Bulletin No. 9 (1967), “Suburban and Farm Vegetable Gardens,” tables 4 and 5. How we match the table.
Nearby in Colorado
- Commerce City 8 mi · last frost May 3
- Denver 11 mi · last frost May 4
- Arvada 13 mi · last frost May 5
- Boulder 18 mi · last frost May 6
- Lakewood 18 mi · last frost May 3
Updated