Michigan frost dates: U
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| Ubly | May 5 | Oct 19 | 167 d | 6a |
| Union | Apr 30 | Oct 17 | 170 d | 6a |
| Union City | May 2 | Oct 13 | 164 d | 6a |
| Union Lake | Apr 29 | Oct 20 | 174 d | 6a |
| Union Pier | Apr 19 | Oct 27 | 191 d | 6b |
| Unionville | May 7 | Oct 9 | 155 d | 6a |
| University Center | Apr 26 | Oct 17 | 174 d | 6a |
| Utica | Apr 26 | Oct 22 | 179 d | 6a |