Montana frost dates: R
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| Radersburg | May 19 | Sep 19 | 123 d | 5a |
| Ramsay | Jun 13 | Sep 5 | 84 d | 4b |
| Rapelje | May 24 | Sep 21 | 120 d | 4b |
| Ravalli | May 12 | Oct 2 | 143 d | 6a |
| Raymond | May 25 | Sep 14 | 112 d | 4a |
| Raynesford | May 22 | Sep 23 | 124 d | 4b |
| Red Lodge | Jun 3 | Sep 19 | 108 d | 5a |
| Redstone | May 28 | Sep 7 | 102 d | 3b |
| Reed Point | May 27 | Sep 14 | 110 d | 5a |
| Reserve | May 16 | Sep 18 | 125 d | 3b |
| Rexford | May 11 | Sep 27 | 139 d | 5b |
| Richey | May 16 | Sep 22 | 129 d | 4a |
| Richland | Jun 5 | Sep 2 | 89 d | 3b |
| Ringling | frost any month | 4b | ||
| Roberts | May 29 | Sep 15 | 109 d | 5a |
| Rollins | May 1 | Oct 15 | 167 d | 6a |
| Ronan | May 10 | Oct 5 | 148 d | 6a |
| Roscoe | Jun 5 | Sep 14 | 101 d | 5a |
| Rosebud | May 9 | Sep 29 | 143 d | 4b |
| Roundup | May 20 | Sep 21 | 124 d | 4b |
| Roy | May 14 | Sep 24 | 133 d | 4b |
| Rudyard | May 21 | Sep 19 | 121 d | 3b |
| Ryegate | May 17 | Sep 23 | 129 d | 4b |