Oregon frost dates: O
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| O Brien | May 1 | Oct 12 | 164 d | 8b |
| Oakland | Mar 31 | Nov 5 | 219 d | 8b |
| Oakridge | Apr 24 | Oct 24 | 183 d | 8b |
| Oceanside | Apr 22 | Oct 21 | 182 d | 9a |
| Odell | Apr 20 | Oct 13 | 176 d | 7b |
| Ontario | Apr 22 | Oct 9 | 170 d | 7a |
| Ophir | Feb 16 | Dec 16 | 303 d | 9b |
| Oregon City | Mar 18 | Nov 18 | 245 d | 9a |
| Otis | Apr 4 | Nov 16 | 226 d | 9a |
| Otter Rock | Mar 12 | Dec 10 | 273 d | 9a |
| Oxbow | Apr 2 | Nov 5 | 217 d | 7a |