Montana frost dates: M
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| Malmstrom Afb | May 6 | Oct 1 | 148 d | 4b |
| Malta | May 10 | Sep 29 | 142 d | 4a |
| Manhattan | May 26 | Sep 15 | 112 d | 5a |
| Marion | frost any month | 4b | ||
| Martin City | May 9 | Oct 1 | 145 d | 5b |
| Martinsdale | Jun 3 | Sep 8 | 97 d | 4b |
| Marysville | Jun 4 | Sep 14 | 102 d | 4b |
| Mc Allister | Jun 16 | Sep 4 | 80 d | 5a |
| Mc Leod | Jun 1 | Sep 11 | 102 d | 5a |
| Medicine Lake | May 16 | Sep 18 | 125 d | 3b |
| Melrose | frost any month | 5a | ||
| Melstone | May 10 | Sep 29 | 142 d | 4b |
| Melville | Jun 9 | Sep 7 | 90 d | 4b |
| Mildred | May 20 | Sep 22 | 125 d | |
| Miles City | May 8 | Sep 30 | 145 d | 4b |
| Milltown | May 10 | Oct 1 | 144 d | 5b |
| Missoula | May 10 | Oct 1 | 144 d | 5b |
| Moccasin | May 28 | Sep 20 | 115 d | 4b |
| Molt | May 24 | Sep 21 | 120 d | 4b |
| Monarch | Jun 6 | Sep 12 | 98 d | 4b |
| Moore | May 23 | Sep 21 | 121 d | 4b |
| Mosby | May 5 | Oct 4 | 152 d | 4b |
| Musselshell | May 10 | Sep 29 | 142 d | 4b |