Indiana frost dates: O
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| Oakford | Apr 27 | Oct 18 | 174 d | 6a |
| Oakland City | Apr 20 | Oct 22 | 185 d | 7a |
| Oaktown | Apr 9 | Oct 30 | 204 d | 6b |
| Oakville | Apr 16 | Oct 25 | 192 d | 6a |
| Odon | Apr 9 | Oct 25 | 199 d | 6b |
| Oldenburg | Apr 20 | Oct 21 | 184 d | 6b |
| Onward | Apr 20 | Oct 23 | 186 d | 6a |
| Oolitic | Apr 20 | Oct 20 | 183 d | 6b |
| Ora | Apr 26 | Oct 19 | 176 d | 5b |
| Orestes | Apr 24 | Oct 18 | 177 d | 6a |
| Orland | Apr 30 | Oct 16 | 169 d | 6a |
| Orleans | Apr 21 | Oct 18 | 180 d | 6b |
| Osceola | Apr 23 | Oct 23 | 183 d | 6a |
| Osgood | Apr 30 | Oct 16 | 169 d | 6b |
| Ossian | Apr 24 | Oct 20 | 179 d | 6a |
| Otisco | Apr 18 | Oct 20 | 185 d | 6b |
| Otterbein | Apr 26 | Oct 12 | 169 d | 6a |
| Otwell | Apr 20 | Oct 22 | 185 d | 6b |
| Owensburg | Apr 9 | Oct 31 | 205 d | 6b |
| Owensville | Apr 13 | Oct 25 | 195 d | 6b |
| Oxford | Apr 25 | Oct 13 | 171 d | 6a |