Michigan frost dates: R
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| Ralph | May 13 | Oct 2 | 142 d | 4b |
| Ramsay | May 19 | Sep 28 | 132 d | 4a |
| Rapid City | May 24 | Oct 1 | 130 d | 6a |
| Rapid River | May 18 | Oct 4 | 139 d | 5a |
| Ravenna | May 14 | Sep 29 | 138 d | 6a |
| Ray | May 1 | Oct 20 | 172 d | 6a |
| Reading | May 3 | Oct 12 | 162 d | 6a |
| Redford | May 1 | Oct 17 | 169 d | 6b |
| Reed City | May 13 | Oct 2 | 142 d | 5a |
| Reese | May 9 | Oct 7 | 151 d | 6a |
| Remus | May 13 | Oct 2 | 142 d | 5b |
| Republic | frost any month | 4a | ||
| Rhodes | May 9 | Oct 4 | 148 d | 6a |
| Richland | Apr 29 | Oct 20 | 174 d | 6a |
| Richmond | May 1 | Oct 20 | 172 d | 6a |
| Richville | May 9 | Oct 7 | 151 d | 6a |
| Riga | Apr 29 | Oct 13 | 167 d | 6a |
| River Rouge | Apr 27 | Oct 25 | 181 d | 6b |
| Riverdale | May 1 | Oct 13 | 165 d | 6a |
| Riverside | May 5 | Oct 15 | 163 d | 6b |
| Riverview | Apr 20 | Oct 27 | 190 d | 6b |
| Rives Junction | May 1 | Oct 14 | 166 d | 6a |
| Rochester | Apr 26 | Oct 22 | 179 d | 6a |
| Rock | May 18 | Oct 4 | 139 d | 5a |
| Rockford | May 6 | Oct 10 | 157 d | 6a |
| Rockland | May 27 | Oct 1 | 127 d | 4b |
| Rockwood | Apr 27 | Oct 22 | 178 d | 6b |
| Rodney | May 13 | Oct 2 | 142 d | 5b |
| Rogers City | May 10 | Oct 14 | 157 d | 6a |
| Romeo | May 1 | Oct 20 | 172 d | 6a |
| Romulus | Apr 20 | Oct 27 | 190 d | 6b |
| Roscommon | May 19 | Sep 23 | 127 d | 5a |
| Rose City | May 21 | Sep 29 | 131 d | 5a |
| Rosebush | Apr 30 | Oct 20 | 173 d | 6a |
| Roseville | Apr 29 | Oct 22 | 176 d | 6b |
| Rothbury | May 19 | Oct 4 | 138 d | 6a |
| Royal Oak | Apr 21 | Oct 31 | 193 d | 6b |
| Rudyard | May 24 | Oct 1 | 130 d | 4b |
| Rumely | May 30 | Sep 27 | 120 d | 5a |
| Ruth | May 2 | Oct 24 | 175 d | 6a |