South Dakota frost dates: O
| City | Last frost | First frost | Season | Zone |
|---|---|---|---|---|
| Oacoma | May 1 | Oct 7 | 159 d | 5a |
| Oelrichs | May 15 | Sep 30 | 138 d | 5a |
| Oglala | May 7 | Oct 4 | 150 d | 5a |
| Okaton | May 3 | Oct 9 | 159 d | 5a |
| Okreek | May 10 | Oct 1 | 144 d | 5a |
| Oldham | May 3 | Oct 2 | 152 d | 4b |
| Olivet | May 1 | Oct 4 | 156 d | 5a |
| Onaka | May 7 | Oct 3 | 149 d | 4b |
| Onida | May 8 | Oct 2 | 147 d | 4b |
| Oral | May 15 | Sep 27 | 135 d | 5a |
| Orient | May 10 | Sep 28 | 141 d | 4b |
| Ortley | May 14 | Sep 28 | 137 d | 4b |
| Owanka | May 10 | Oct 1 | 144 d | 5a |