Hardiness zones
USDA hardiness zones are based on the average coldest winter night. They tell you which perennials survive winter; your frost dates tell you when to plant.
| Zone | Typical last frost | Typical first frost | Season |
|---|---|---|---|
| Zone 2a | May 24 | Sep 6 | 105 days |
| Zone 3b | May 17 | Sep 24 | 130 days |
| Zone 4a | May 12 | Sep 28 | 139 days |
| Zone 4b | May 8 | Oct 1 | 146 days |
| Zone 5a | May 3 | Oct 5 | 155 days |
| Zone 5b | May 1 | Oct 11 | 163 days |
| Zone 6a | Apr 29 | Oct 17 | 171 days |
| Zone 6b | Apr 22 | Oct 22 | 183 days |
| Zone 7a | Apr 16 | Oct 25 | 192 days |
| Zone 7b | Apr 5 | Nov 1 | 210 days |
| Zone 8a | Mar 29 | Nov 7 | 223 days |
| Zone 8b | Mar 16 | Nov 14 | 243 days |
| Zone 9a | Mar 3 | Nov 25 | 267 days |
| Zone 9b | Feb 20 | Dec 5 | 288 days |
| Zone 10a | Mar 2 | Dec 1 | 274 days |