Idaho frost dates: R
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| Rathdrum | Apr 22 | Oct 18 | 179 d | 6b |
| Reubens | May 23 | Sep 25 | 125 d | 6b |
| Rexburg | May 12 | Sep 24 | 135 d | 5a |
| Richfield | May 24 | Sep 26 | 125 d | 6a |
| Rigby | May 9 | Oct 5 | 149 d | 5b |
| Riggins | May 6 | Oct 9 | 156 d | 6b |
| Ririe | frost any month | 5b | ||
| Roberts | May 9 | Oct 5 | 149 d | 5a |
| Rockland | May 20 | Sep 26 | 129 d | 6a |
| Rogerson | frost any month | 6a | ||
| Rupert | May 16 | Oct 1 | 138 d | 6a |