The 26 zones
Zones are USDA's 2023 map: each number-half is a 5°F band of average annual extreme minimum temperature.
| Zone | Avg coldest night | US ZIPs | Last spring freeze | First fall freeze |
|---|---|---|---|---|
| 1a | -60 to -55°F | 5 | no freeze | year-round |
| 1b | -55 to -50°F | 11 | no freeze | year-round |
| 2a | -50 to -45°F | 27 | no freeze | year-round |
| 2b | -45 to -40°F | 17 | no freeze | year-round |
| 3a | -40 to -35°F | 23 | May 25 | Sep 17 |
| 3b | -35 to -30°F | 230 | May 19 | Sep 21 |
| 4a | -30 to -25°F | 814 | May 15 | Sep 24 |
| 4b | -25 to -20°F | 1,284 | May 12 | Sep 27 |
| 5a | -20 to -15°F | 2,426 | May 7 | Sep 30 |
| 5b | -15 to -10°F | 2,880 | May 5 | Oct 4 |
| 6a | -10 to -5°F | 5,187 | May 1 | Oct 10 |
| 6b | -5 to 0°F | 5,271 | Apr 25 | Oct 16 |
| 7a | 0 to 5°F | 4,877 | Apr 20 | Oct 20 |
| 7b | 5 to 10°F | 3,855 | Apr 10 | Oct 28 |
| 8a | 10 to 15°F | 3,430 | Apr 2 | Nov 5 |
| 8b | 15 to 20°F | 3,379 | Mar 23 | Nov 12 |
| 9a | 20 to 25°F | 2,199 | Mar 5 | Nov 26 |
| 9b | 25 to 30°F | 2,085 | Feb 7 | Dec 10 |
| 10a | 30 to 35°F | 1,234 | Jan 15 | Dec 20 |
| 10b | 35 to 40°F | 752 | Jan 10 | Jan 7 |
| 11a | 40 to 45°F | 205 | Jan 12 | Jan 10 |
| 11b | 45 to 50°F | 16 | no freeze | year-round |
| 12a | 50 to 55°F | 30 | no freeze | year-round |
| 12b | 55 to 60°F | 137 | no freeze | year-round |
| 13a | 60 to 65°F | 102 | no freeze | year-round |
| 13b | 65 to 70°F | 26 | no freeze | year-round |