Colorado planting zones & frost dates
The 16 Colorado cities on this site fall in zones 5b, 6a. Last spring frost dates range from May 4 in Pueblo to May 15 in Loveland.
| City | Zone | Last frost | First frost | Population |
|---|---|---|---|---|
| Denver | 6a | May 8 | Oct 3 | 729,019 |
| Colorado Springs | 6a | May 8 | Oct 3 | 493,554 |
| Aurora | 6a | May 12 | Oct 2 | 403,130 |
| Fort Collins | 5b | May 7 | Oct 2 | 170,924 |
| Lakewood | 6a | May 8 | Oct 2 | 156,868 |
| Thornton | 6a | May 7 | Oct 4 | 146,689 |
| Arvada | 6a | May 11 | Sep 29 | 121,873 |
| Westminster | 6a | May 7 | Oct 4 | 115,302 |
| Greeley | 5b | May 7 | Oct 3 | 114,363 |
| Pueblo | 6a | May 4 | Oct 4 | 111,166 |
| Centennial | 6a | May 10 | Oct 3 | 108,853 |
| Boulder | 6a | May 11 | Sep 30 | 106,803 |
| Longmont | 5b | May 13 | Oct 1 | 99,818 |
| Castle Rock | 5b | May 15 | Sep 27 | 83,213 |
| Loveland | 5b | May 15 | Sep 25 | 81,102 |
| Broomfield | 6a | May 7 | Oct 4 | 78,323 |
Frost dates are 30%-risk dates from the nearest suitable NOAA station. Population: Census Vintage 2024 estimates.