California frost dates: O
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| O Neals | Mar 25 | Dec 3 | 253 d | 9a |
| Oak Park | Jan 24 | Dec 15 | 325 d | 10b |
| Oak Run | Mar 3 | Nov 21 | 263 d | 9a |
| Oak View | Mar 21 | Nov 15 | 239 d | 9b |
| Oakdale | Jan 31 | Dec 5 | 308 d | 9b |
| Oakhurst | Apr 24 | Nov 4 | 194 d | 9a |
| Oakland | rare frost | 10a | ||
| Oakley | Jan 12 | Dec 19 | 341 d | 9b |
| Oakville | Feb 3 | Dec 4 | 304 d | 9b |
| Obrien | Feb 8 | Dec 28 | 323 d | 9a |
| Occidental | Jan 29 | Dec 30 | 335 d | 10a |
| Oceano | Feb 1 | Jan 4 | 337 d | 10a |
| Oceanside | Jan 23 | Dec 11 | 322 d | 10a |
| Ocotillo | Jan 6 | Dec 21 | 349 d | 10a |
| Ojai | Mar 21 | Nov 15 | 239 d | 8b |
| Olancha | Apr 17 | Nov 1 | 198 d | 8b |
| Old Station | Jun 9 | Sep 21 | 104 d | 7a |
| Olema | Jan 11 | Dec 21 | 344 d | 9b |
| Olivehurst | Feb 11 | Nov 30 | 292 d | 9b |
| Olympic Valley | Jun 9 | Sep 25 | 108 d | 7a |
| Ontario | Jan 4 | Dec 30 | 360 d | 10a |
| Onyx | Apr 5 | Nov 3 | 212 d | 9a |
| Orange | rare frost | 10b | ||
| Orange Cove | Jan 23 | Dec 13 | 324 d | 9b |
| Orangevale | Jan 12 | Dec 16 | 338 d | 9b |
| Oregon House | Apr 1 | Nov 17 | 230 d | 9b |
| Orick | Apr 12 | Nov 6 | 208 d | 9b |
| Orinda | Jan 3 | Jan 1 | 363 d | 9b |
| Orland | Feb 25 | Dec 2 | 280 d | 9b |
| Orleans | Mar 12 | Nov 26 | 259 d | 9a |
| Oro Grande | Mar 18 | Nov 11 | 238 d | 8b |
| Orosi | Jan 23 | Dec 13 | 324 d | 9b |
| Oroville | Jan 30 | Dec 13 | 317 d | 9b |
| Oxnard | rare frost | 10b | ||