Colorado frost dates: B
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| Bailey | Jun 16 | Sep 8 | 84 d | 5b |
| Basalt | May 31 | Sep 23 | 115 d | 6a |
| Battlement Mesa | May 17 | Sep 30 | 136 d | 6b |
| Bayfield | May 31 | Sep 26 | 118 d | 6a |
| Bedrock | May 11 | Oct 5 | 147 d | 6b |
| Bellvue | May 21 | Sep 29 | 131 d | 5b |
| Bennett | May 5 | Oct 9 | 157 d | 6a |
| Berthoud | May 7 | Oct 5 | 151 d | 5b |
| Bethune | May 6 | Oct 9 | 156 d | 6a |
| Beulah | May 5 | Oct 10 | 158 d | 6a |
| Black Hawk | Jun 5 | Sep 16 | 103 d | 5b |
| Blanca | May 25 | Sep 22 | 120 d | 5a |
| Boncarbo | May 11 | Oct 4 | 146 d | 6a |
| Bond | Jun 6 | Sep 14 | 100 d | 5b |
| Boone | May 5 | Oct 6 | 154 d | 6a |
| Boulder | May 6 | Oct 5 | 152 d | 6a |
| Branson | May 17 | Oct 1 | 137 d | 6a |
| Breckenridge | frost any month | 5a | ||
| Briggsdale | May 12 | Sep 28 | 139 d | 5a |
| Brighton | May 3 | Oct 7 | 157 d | 5b |
| Broomfield | May 2 | Oct 11 | 162 d | 6a |
| Brush | May 6 | Oct 6 | 153 d | 5b |
| Buena Vista | May 27 | Sep 23 | 119 d | 5b |
| Buffalo Creek | May 16 | Sep 29 | 136 d | 5b |
| Burlington | May 6 | Oct 9 | 156 d | 6a |
| Burns | Jun 14 | Sep 11 | 89 d | 5b |
| Byers | May 13 | Oct 2 | 142 d | 5b |