Maryland frost dates: U
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| Union Bridge | Apr 22 | Oct 20 | 181 d | 7a |
| Unionville | Apr 2 | Nov 6 | 218 d | 7b |
| Upper Fairmount | Apr 3 | Nov 7 | 218 d | 8a |
| Upper Falls | Apr 10 | Oct 30 | 203 d | 7b |
| Upper Marlboro | Apr 9 | Oct 29 | 203 d | 7b |
| Upperco | Apr 19 | Oct 25 | 189 d | 7a |