USDA hardiness zone 4a
In zone 4a the average coldest winter night reaches -30°F to -25°F. Plants labeled for zone 4 (or a colder zone) can survive the winter outdoors here. 15 U.S. cities with 10,000+ residents are in this zone.
| City | State | Zone | Avg. last frost | Avg. first frost |
|---|---|---|---|---|
| Fargo | ND | 4a | May 5 | Oct 3 |
| Bismarck | ND | 4a | May 10 | Sep 30 |
| Grand Forks | ND | 4a | May 10 | Oct 1 |
| Minot | ND | 4a | May 10 | Oct 1 |
| Moorhead | MN | 4a | May 5 | Oct 3 |
| West Fargo | ND | 4a | May 10 | Sep 30 |
| Laramie | WY | 4a | Jun 7 | Sep 4 |
| Aberdeen | SD | 4a | May 8 | Sep 29 |
| Williston | ND | 4a | May 21 | Sep 21 |
| Dickinson | ND | 4a | May 20 | Sep 22 |
| Mandan | ND | 4a | May 13 | Sep 27 |
| Brainerd | MN | 4a | May 8 | Sep 29 |
| Fergus Falls | MN | 4a | May 4 | Oct 5 |
| Cloquet | MN | 4a | May 26 | Sep 23 |
| Grand Rapids | MN | 4a | May 17 | Sep 24 |