Iowa frost dates: R
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| Radcliffe | Apr 28 | Oct 10 | 165 d | 5a |
| Rake | Apr 30 | Oct 7 | 160 d | 5a |
| Ralston | Apr 27 | Oct 10 | 166 d | 5a |
| Randalia | May 4 | Oct 4 | 153 d | 5a |
| Randall | Apr 26 | Oct 8 | 165 d | 5a |
| Randolph | Apr 19 | Oct 19 | 183 d | 5b |
| Raymond | Apr 27 | Oct 10 | 166 d | 5a |
| Readlyn | Apr 29 | Oct 9 | 163 d | 5a |
| Reasnor | Apr 22 | Oct 17 | 178 d | 5b |
| Red Oak | Apr 24 | Oct 13 | 172 d | 5b |
| Redding | Apr 24 | Oct 14 | 173 d | 5b |
| Redfield | May 2 | Oct 3 | 154 d | 5a |
| Reinbeck | Apr 29 | Oct 9 | 163 d | 5a |
| Rembrandt | Apr 30 | Oct 5 | 158 d | 5a |
| Remsen | Apr 30 | Oct 4 | 157 d | 5a |
| Renwick | Apr 26 | Oct 12 | 169 d | 5a |
| Rhodes | Apr 24 | Oct 12 | 171 d | 5b |
| Riceville | Apr 30 | Oct 9 | 162 d | 4b |
| Richland | Apr 27 | Oct 12 | 168 d | 5b |
| Ricketts | May 3 | Oct 1 | 151 d | 5a |
| Ridgeway | May 8 | Oct 1 | 146 d | 4b |
| Ringsted | May 2 | Oct 3 | 154 d | 5a |
| Rippey | Apr 25 | Oct 10 | 168 d | 5a |
| Riverside | Apr 29 | Oct 9 | 163 d | 5b |
| Riverton | Apr 19 | Oct 19 | 183 d | 5b |
| Robins | Apr 28 | Oct 12 | 167 d | 5a |
| Rock Falls | Apr 29 | Oct 7 | 161 d | 5a |
| Rock Rapids | May 1 | Oct 4 | 156 d | 5a |
| Rock Valley | Apr 30 | Oct 3 | 156 d | 5a |
| Rockford | Apr 30 | Oct 6 | 159 d | 5a |
| Rockwell | Apr 29 | Oct 7 | 161 d | 5a |
| Rockwell City | Apr 26 | Oct 10 | 167 d | 5a |
| Rodney | May 3 | Oct 1 | 151 d | 5a |
| Roland | Apr 26 | Oct 8 | 165 d | 5a |
| Rolfe | Apr 26 | Oct 7 | 164 d | 5a |
| Rome | Apr 30 | Oct 10 | 163 d | 5b |
| Rose Hill | Apr 21 | Oct 16 | 178 d | 5b |
| Rowan | Apr 30 | Oct 10 | 163 d | 5a |
| Rowley | Apr 30 | Oct 7 | 160 d | 5a |
| Royal | May 2 | Oct 2 | 153 d | 5a |
| Rudd | Apr 30 | Oct 9 | 162 d | 5a |
| Runnells | Apr 21 | Oct 15 | 177 d | 5b |
| Russell | May 5 | Oct 5 | 153 d | 5b |
| Ruthven | Apr 27 | Oct 7 | 163 d | 5a |
| Rutland | Apr 27 | Oct 9 | 165 d | 5a |
| Ryan | May 3 | Oct 7 | 157 d | 5a |