Maryland frost dates: O
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| Oakland | May 6 | Oct 9 | 156 d | 6a |
| Ocean City | Apr 7 | Nov 2 | 209 d | 8a |
| Odenton | Apr 10 | Oct 31 | 204 d | 7b |
| Oldtown | Apr 15 | Oct 24 | 192 d | 7a |
| Olney | Apr 1 | Nov 6 | 219 d | 7b |
| Owings | Apr 9 | Oct 29 | 203 d | 7b |
| Owings Mills | Apr 2 | Nov 7 | 219 d | 7a |
| Oxford | Apr 1 | Nov 7 | 220 d | 8a |
| Oxon Hill | Apr 3 | Nov 8 | 219 d | 7b |