When Is the Last Frost in Wyoming?
The average last spring frost in Wyoming falls between May 12 and June 14 for most ZIP codes, with a statewide median of May 22. At the average date a later frost is still a coin flip, so tender plants wait for the safer 90% date.
| City | Last frost | 90% safe after | First frost | Growing season |
|---|---|---|---|---|
| Cheyenne | May 14 | May 28 | Oct 1 | 139 days |
| Casper | May 10 | May 24 | Sep 29 | 138 days |
| Gillette | May 15 | May 27 | Oct 1 | 136 days |
| Laramie | Jun 7 | Jun 29 | Sep 4 | 88 days |
| Rock Springs | May 24 | Jun 9 | Sep 24 | 121 days |
| Sheridan | May 18 | Jun 2 | Sep 24 | 127 days |
| Evanston | Jun 14 | Jul 1 | Sep 9 | 84 days |
| Green River | May 24 | Jun 10 | Sep 22 | 120 days |
| Riverton | May 12 | May 26 | Sep 24 | 132 days |
| Jackson | Jun 20 | Jul 9 | Aug 31 | 70 days |
| Cody | May 15 | Jun 1 | Sep 25 | 132 days |
| Rawlins | May 12 | May 25 | Oct 4 | 143 days |
| Lander | May 18 | Jun 3 | Sep 27 | 131 days |
| Powell | May 15 | Jun 1 | Sep 25 | 132 days |
| Douglas | May 23 | Jun 7 | Sep 22 | 122 days |
| Torrington | May 11 | May 26 | Sep 29 | 139 days |
| Worland | May 4 | May 18 | Oct 1 | 149 days |
| Buffalo | May 24 | Jun 9 | Sep 21 | 118 days |
Last and first frost: 50% (median) dates of the last spring and first fall 32 °F night. 90% safe after: only a 10% chance of a later spring frost. First frost dates in January fall in the following winter. Each city uses the NOAA station nearest the ZIP code closest to its center.
Across all 129 Wyoming weather stations with frost records, median last frost dates run from April 28 at Basin, WY to June 24 at Moose 1 NNE, WY. Elevation, valleys that collect cold air and distance from large water bodies explain most of the spread, so a garden a few miles from a listed city can differ by a week or more. The ZIP code lookup above uses the same NOAA data as the frost date calculator for every US ZIP code.
When Is the First Frost in Wyoming?
The average first fall frost in Wyoming arrives between September 1 and October 1 for most ZIP codes, with a median of September 23. Tomatoes, peppers, basil and squash are damaged at 32 °F, so harvest or cover them before then.
Fall frost can come early: Cheyenne has a 10% chance of frost before September 17, Casper has a 10% chance of frost before September 14 and Gillette has a 10% chance of frost before September 15. Hardy crops such as kale, spinach and cabbage tolerate light frosts and keep producing after the first frost date.
When to Plant Tomatoes in Wyoming?
Transplant tomatoes in Wyoming 1 to 2 weeks after the local average last frost, once nights stay above about 50 °F: May 21 – May 28 in Cheyenne, May 17 – May 24 in Casper and May 22 – May 29 in Gillette. Start seeds indoors 6 to 8 weeks before the last frost.
| City | Start seeds indoors | Transplant outdoors | Lowest-risk transplant |
|---|---|---|---|
| Cheyenne | Mar 19 – Apr 2 | May 21 – May 28 | after May 28 |
| Casper | Mar 15 – Mar 29 | May 17 – May 24 | after May 24 |
| Gillette | Mar 20 – Apr 3 | May 22 – May 29 | after May 27 |
| Laramie | Apr 12 – Apr 26 | Jun 14 – Jun 21 | after Jun 29 |
| Rock Springs | Mar 29 – Apr 12 | May 31 – Jun 7 | after Jun 9 |
| Sheridan | Mar 23 – Apr 6 | May 25 – Jun 1 | after Jun 2 |
| Evanston | Apr 19 – May 3 | Jun 21 – Jun 28 | after Jul 1 |
| Green River | Mar 29 – Apr 12 | May 31 – Jun 7 | after Jun 10 |
| Riverton | Mar 17 – Mar 31 | May 19 – May 26 | after May 26 |
| Jackson | Apr 25 – May 9 | Jun 27 – Jul 4 | after Jul 9 |
| Cody | Mar 20 – Apr 3 | May 22 – May 29 | after Jun 1 |
| Rawlins | Mar 17 – Mar 31 | May 19 – May 26 | after May 25 |
| Lander | Mar 23 – Apr 6 | May 25 – Jun 1 | after Jun 3 |
| Powell | Mar 20 – Apr 3 | May 22 – May 29 | after Jun 1 |
| Douglas | Mar 28 – Apr 11 | May 30 – Jun 6 | after Jun 7 |
| Torrington | Mar 16 – Mar 30 | May 18 – May 25 | after May 26 |
| Worland | Mar 9 – Mar 23 | May 11 – May 18 | after May 18 |
| Buffalo | Mar 29 – Apr 12 | May 31 – Jun 7 | after Jun 9 |
Indoors: 6–8 weeks before the average last frost. Outdoors: 1–2 weeks after it. Lowest-risk: after the date with only a 10% chance of a later frost. Rules of thumb; check the 10-day forecast and wait for soil near 60 °F.
Tomatoes stall below about 50 °F at night and are killed by frost, so a week or two of waiting after the average date costs little. The tomato plant care guide covers light, watering and feeding once plants are in the ground. With a median growing season of only 121 days, early-maturing varieties, black plastic mulch or a greenhouse help tomatoes ripen before the first fall frost.
What Can You Plant in Cheyenne and When?
Cheyenne's average last frost of May 14 anchors its spring planting calendar: peas and spinach go in from April 2, broccoli and lettuce transplants from April 16, and tomatoes, peppers and squash after May 21.
| Crop | Start seeds indoors | Plant outdoors | Frost tolerance |
|---|---|---|---|
| Peas | — | Apr 2 – Apr 16direct sow, 4–6 weeks before last frost | hardy |
| Spinach | — | Apr 2 – Apr 23direct sow, 3–6 weeks before last frost | hardy |
| Radishes | — | Apr 9 – Apr 23direct sow, 3–5 weeks before last frost | hardy |
| Onions (sets) | — | Apr 16 – Apr 30plant, 2–4 weeks before last frost | hardy |
| Potatoes | — | Apr 16 – Apr 30plant, 2–4 weeks before last frost | half-hardy |
| Broccoli & cabbage | Mar 19 – Apr 2 | Apr 16 – Apr 30transplant, 2–4 weeks before last frost | hardy |
| Lettuce | Apr 2 – Apr 16 | Apr 16 – Apr 30transplant, 2–4 weeks before last frost | hardy |
| Beets | — | Apr 16 – Apr 30direct sow, 2–4 weeks before last frost | half-hardy |
| Carrots | — | Apr 23 – Apr 30direct sow, 2–3 weeks before last frost | half-hardy |
| Tomatoes | Mar 19 – Apr 2 | May 21 – May 28transplant, 1–2 weeks after last frost | tender |
| Basil | Mar 19 – Apr 2 | May 21 – Jun 4transplant, 1–3 weeks after last frost | tender |
| Peppers | Mar 5 – Mar 19 | May 28 – Jun 4transplant, 2–3 weeks after last frost | tender |
| Eggplant | Mar 5 – Mar 19 | May 28 – Jun 4transplant, 2–3 weeks after last frost | tender |
| Green beans | — | May 21 – Jun 4direct sow, 1–3 weeks after last frost | tender |
| Sweet corn | — | May 21 – Jun 4direct sow, 1–3 weeks after last frost | tender |
| Cucumbers | Apr 16 – Apr 23 | May 21 – Jun 4transplant, 1–3 weeks after last frost | tender |
| Squash & zucchini | Apr 16 – Apr 23 | May 21 – Jun 4transplant, 1–3 weeks after last frost | tender |
| Watermelon | Apr 16 – Apr 23 | May 28 – Jun 4transplant, 2–3 weeks after last frost | tender |
Dates for Cheyenne (last frost May 14, NOAA station Cheyenne WFO, WY, 3 miles from ZIP 82005). General rules of thumb; wait for soil near 50 °F for most seeds and 60 °F for beans, corn and squash.
How Long Is the Growing Season in Wyoming?
The frost-free growing season in Wyoming lasts about 76 to 142 days for most ZIP codes, with a median of 121 days. Among the listed cities, Jackson has the shortest season at 70 days and Worland the longest at 149.
Season length decides which varieties ripen: compare it with the “days to maturity” on seed packets, counted from transplanting for tomatoes and peppers. NOAA stations in Wyoming range from 63 days at Moose 1 NNE, WY to 164 days at Basin, WY. Planning beds before the season starts helps in short seasons — a plant spacing calculator for vegetable beds shows how many transplants fit.
What Hardiness Zones Are in Wyoming?
Wyoming spans USDA hardiness zones 4a to 5b, with zone 5a the most common. Zones describe winter cold and decide which perennials survive, while frost dates set when to plant annual vegetables and flowers.
The Wyoming planting zone map with the zone of each city shows how the zones are spread across the state and which plants are hardy in all of them.
Frequently Asked Questions
- When is the last frost in Wyoming?
- The average last spring frost in Wyoming falls between May 12 and June 14 for most ZIP codes, with a statewide median of May 22. Among major cities it ranges from May 4 in Worland to June 20 in Jackson.
- When is the last frost in Cheyenne, Wyoming?
- Cheyenne's average last spring frost is May 14, and by May 28 the chance of a later frost drops to 10%. Its first fall frost averages October 1, giving a 139-day growing season (NOAA station Cheyenne WFO, WY).
- When should you plant tomatoes in Wyoming?
- Transplant tomatoes in Wyoming 1 to 2 weeks after the local average last frost, once nights stay above about 50 °F: May 21 – May 28 in Cheyenne, May 17 – May 24 in Casper and May 22 – May 29 in Gillette. Start seeds indoors 6 to 8 weeks before the last frost.
- When is the first frost in Wyoming?
- The average first fall frost in Wyoming arrives between September 1 and October 1 for most ZIP codes, with a median of September 23. Harvest tender crops such as tomatoes, peppers and basil before then or cover them on cold nights.
- How long is the growing season in Wyoming?
- The frost-free growing season in Wyoming lasts about 76 to 142 days for most ZIP codes, with a median of 121 days, from 70 days in Jackson to 149 days in Worland.
Frost data: NOAA National Centers for Environmental Information, 1991–2020 U.S. Climate Normals (32 °F freeze dates by probability). ZIP code and city locations and populations: U.S. Census Bureau Gazetteer files and Vintage 2024 population estimates. Planting windows are general rules of thumb. PlantoScan is not affiliated with or endorsed by these agencies.