Iowa frost dates: U
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| Udell | Apr 18 | Oct 23 | 188 d | 5b |
| Underwood | Apr 23 | Oct 14 | 174 d | 5b |
| Union | Apr 27 | Oct 10 | 166 d | 5a |
| Unionville | Apr 18 | Oct 23 | 188 d | 5b |
| University Park | Apr 21 | Oct 16 | 178 d | 5b |
| Urbana | May 3 | Oct 3 | 153 d | 5a |
| Urbandale | Apr 19 | Oct 18 | 182 d | 5b |
| Ute | Apr 25 | Oct 12 | 170 d | 5a |