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Wyoming frost dates
Across the 19Wyoming weather stations below, the average last spring frost ranges from May 4 in Greybull S Big Horn to Jun 24 in Moose 1 Nne. The statewide middle is about May 22 for the last spring frost and Sep 26 for the first fall frost. Greybull S Big Horn has the longest growing season, about 150 days. Hardiness zones in these places: 4a, 4b, 5a, 5b.
Frost dates by city
| Place | Zone | Last spring frost | 90% safe after | First fall frost | Frost-free days |
|---|---|---|---|---|---|
| Greybull S Big Horn | 4b | May 4 | May 18 | Oct 1 | 150 |
| Torrington | 5a | May 11 | May 26 | Sep 29 | 141 |
| Cheyenne | 5b | May 12 | May 26 | Oct 1 | 142 |
| Buffalo Johnson | 5a | May 13 | May 28 | Oct 1 | 141 |
| Lander 11 Sse | 5a | May 13 | Jun 1 | Oct 2 | 142 |
| Worland | 4b | May 13 | May 27 | Sep 26 | 136 |
| Riverton | 5a | May 16 | May 31 | Sep 28 | 135 |
| Lander Hunt | 5a | May 18 | Jun 3 | Sep 27 | 132 |
| Sheridan | 5a | May 21 | Jun 6 | Sep 23 | 125 |
| Gillette Campbell | 5a | May 22 | Jun 4 | Sep 25 | 126 |
| Moorcroft 3S | 4b | May 22 | Jun 9 | Sep 28 | 129 |
| Rock Springs | 5a | May 22 | Jun 9 | Sep 28 | 129 |
| Douglas Converse | 5a | May 23 | Jun 7 | Sep 22 | 122 |
| Sundance 8 Nnw | 4b | May 23 | Jun 3 | Sep 24 | 124 |
| Casper Natrona | 5a | May 26 | Jun 10 | Sep 22 | 119 |
| Rawlins | 5a | Jun 1 | Jun 17 | Sep 15 | 106 |
| Laramie | 4a | Jun 2 | Jun 18 | Sep 15 | 105 |
| Evanston Burns | 5a | Jun 3 | Jun 17 | Sep 25 | 114 |
| Moose 1 Nne | 4a | Jun 24 | Jul 11 | Aug 28 | 65 |
Dates are the 50% probability of a 32°F freeze (NOAA 1991–2020 normals); "90% safe after" is the date after which a later spring freeze happens in only 1 year in 10.
When to plant in Wyoming
Using the statewide middle dates (last frost May 22, first frost Sep 26). Adjust for your town with the table above or the planting calendar.
| Plant | When to plant in Wyoming |
|---|---|
| Tomatoes | May 29 – Jun 12 |
| Peas | Apr 10 – May 1; fall: Jul 4 – Jul 25 |
| Potatoes | Apr 24 – May 15 |
| Green beans | May 29 – Jun 12; fall: Jul 11 – Jul 25 |
| Garlic | Sep 26 – Oct 24 |
| Tulips | Sep 12 – Oct 24 |