Missouri frost dates: O
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| O Fallon | Apr 10 | Oct 26 | 199 d | 6b |
| Oak Grove | Apr 13 | Oct 23 | 193 d | 6a |
| Oak Ridge | Apr 7 | Oct 29 | 205 d | 7a |
| Odessa | Apr 13 | Oct 23 | 193 d | 6b |
| Old Appleton | Apr 19 | Oct 20 | 184 d | 7a |
| Old Monroe | Apr 20 | Oct 20 | 183 d | 6b |
| Oldfield | Apr 26 | Oct 13 | 170 d | 6b |
| Olean | Apr 7 | Nov 1 | 208 d | 6b |
| Olney | Apr 14 | Oct 23 | 192 d | 6b |
| Oran | Apr 5 | Oct 25 | 203 d | 7a |
| Oregon | Apr 16 | Oct 20 | 187 d | 6a |
| Oronogo | Apr 9 | Oct 27 | 201 d | 7a |
| Orrick | Apr 19 | Oct 18 | 182 d | 6a |
| Osage Beach | Mar 31 | Nov 3 | 217 d | 7a |
| Osborn | Apr 19 | Oct 19 | 183 d | 6a |
| Osceola | Apr 16 | Oct 24 | 191 d | 6b |
| Otterville | Apr 10 | Oct 26 | 199 d | 6b |
| Owensville | Apr 27 | Oct 13 | 169 d | 6b |
| Oxly | Apr 12 | Oct 26 | 197 d | 7a |
| Ozark | Apr 15 | Oct 23 | 191 d | 6b |