Montana frost dates: S
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| Saco | May 15 | Sep 23 | 131 d | 3b |
| Saint Ignatius | May 12 | Oct 2 | 143 d | 6a |
| Saint Marie | May 13 | Sep 27 | 137 d | 4a |
| Saint Regis | frost any month | 6a | ||
| Saint Xavier | May 7 | Oct 5 | 151 d | 5a |
| Saltese | frost any month | 6a | ||
| Sand Coulee | May 6 | Oct 1 | 148 d | 4b |
| Sand Springs | May 5 | Oct 4 | 152 d | 4b |
| Sanders | May 10 | Sep 29 | 142 d | 4b |
| Savage | May 12 | Sep 25 | 136 d | 4a |
| Scobey | May 28 | Sep 6 | 101 d | 3b |
| Seeley Lake | frost any month | 5a | ||
| Shawmut | May 23 | Sep 16 | 116 d | 4b |
| Shelby | May 23 | Sep 16 | 116 d | 4a |
| Shepherd | May 12 | Sep 25 | 136 d | 4b |
| Sheridan | May 24 | Sep 22 | 121 d | 5a |
| Sidney | May 11 | Sep 27 | 139 d | 4a |
| Silver Gate | frost any month | 4a | ||
| Silver Star | Jun 8 | Sep 2 | 86 d | 5a |
| Simms | Jun 2 | Sep 10 | 100 d | 4b |
| Somers | May 12 | Sep 25 | 136 d | 6a |
| Springdale | May 27 | Sep 14 | 110 d | 5a |
| Stanford | May 25 | Sep 21 | 119 d | 4b |
| Stevensville | May 22 | Sep 19 | 120 d | 5b |
| Stockett | May 6 | Oct 1 | 148 d | 4b |
| Stryker | May 16 | Sep 18 | 125 d | 5a |
| Sula | frost any month | 5a | ||
| Sumatra | May 10 | Sep 29 | 142 d | 4b |
| Sun River | Jun 2 | Sep 10 | 100 d | 4a |
| Sunburst | May 17 | Sep 25 | 131 d | 4a |
| Superior | May 17 | Sep 23 | 129 d | 6a |
| Sweet Grass | May 15 | Sep 25 | 133 d | 4a |