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Montana frost dates
Across the 22Montana weather stations below, the average last spring frost ranges from May 4 in Billings Logan to Jun 15 in Lewistown 42 Wsw. The statewide middle is about May 18 for the last spring frost and Sep 22 for the first fall frost. Billings Logan has the longest growing season, about 156 days. Hardiness zones in these places: 3b, 4a, 4b, 5a, 5b, 6a.
Frost dates by city
| Place | Zone | Last spring frost | 90% safe after | First fall frost | Frost-free days |
|---|---|---|---|---|---|
| Billings Logan | 5a | May 4 | May 18 | Oct 7 | 156 |
| Glasgow | 4a | May 6 | May 18 | Sep 30 | 147 |
| Miles F Wiley | 4b | May 8 | May 21 | Sep 30 | 145 |
| Helena | 4b | May 9 | May 25 | Sep 30 | 144 |
| Marie | 4a | May 13 | May 26 | Sep 27 | 137 |
| Wolf Point 34 Ne | 4a | May 13 | May 25 | Sep 28 | 138 |
| Havre | 3b | May 15 | May 27 | Sep 23 | 131 |
| Baker | 4b | May 16 | May 29 | Sep 26 | 133 |
| Missoula | 5b | May 16 | Jun 1 | Sep 26 | 133 |
| Wolf Point | 4a | May 16 | May 29 | Sep 20 | 127 |
| Superior | 6a | May 17 | Jun 8 | Sep 23 | 129 |
| Jordan | 4a | May 18 | May 31 | Sep 20 | 125 |
| Great Falls | 4b | May 19 | Jun 2 | Sep 24 | 128 |
| Lewistown | 4b | May 23 | Jun 8 | Sep 21 | 121 |
| Cut Bank | 4a | May 24 | Jun 5 | Sep 15 | 114 |
| Wolf Point 29 Ene | 4a | May 24 | Jun 6 | Sep 14 | 113 |
| Bozeman Gallatin | 5a | May 26 | Jun 12 | Sep 16 | 113 |
| Livingston Mission | 5a | May 27 | Jun 14 | Sep 14 | 110 |
| Dillon | 4b | Jun 2 | Jun 21 | Sep 13 | 103 |
| . Mary 1 Ssw | 4b | Jun 3 | Jun 23 | Sep 8 | 97 |
| Butte Bert Mooney | 5a | Jun 13 | Jul 1 | Sep 5 | 84 |
| Lewistown 42 Wsw | 4b | Jun 15 | Jul 8 | Sep 4 | 81 |
Dates are the 50% probability of a 32°F freeze (NOAA 1991–2020 normals); "90% safe after" is the date after which a later spring freeze happens in only 1 year in 10.
When to plant in Montana
Using the statewide middle dates (last frost May 18, first frost Sep 22). Adjust for your town with the table above or the planting calendar.
| Plant | When to plant in Montana |
|---|---|
| Tomatoes | May 25 – Jun 8 |
| Peas | Apr 6 – Apr 27; fall: Jun 30 – Jul 21 |
| Potatoes | Apr 20 – May 11 |
| Green beans | May 25 – Jun 8; fall: Jul 7 – Jul 21 |
| Garlic | Sep 22 – Oct 20 |
| Tulips | Sep 8 – Oct 20 |