In Wyoming, the last spring frost usually comes between May 15 and June 11, and the first fall frost between September 3 and September 27, depending on where you live. Most of Wyoming is in USDA hardiness zones 4b to 5b. In the highest mountain areas, frost is possible in any month.
Find the frost dates for your ZIP code
Frost dates from NOAA 1991–2020 U.S. Climate Normals, nearest weather station. Zones derived from the 2023 USDA Plant Hardiness Zone Map data (PRISM Climate Group, Oregon State University). This is not the official USDA Plant Hardiness Zone Map.
Frost dates for Wyoming cities
Dates come from the NOAA weather station closest to each city. The last spring frost and first fall frost are the typical dates, with a 30% chance of frost after (or before) them. The safer planting date has only a 10% chance of a later spring frost: use it for tender plants like tomatoes, peppers and basil.
| City | Zone | Last frost | Safer date | First frost |
|---|---|---|---|---|
| Cheyenne | 5b | May 20 | May 28 | Sep. 26 |
| Casper | 5a | May 16 | May 24 | Sep. 23 |
| Gillette | 4b | May 21 | May 27 | Sep. 25 |
| Laramie | 4a | June 15 | June 29 | Aug. 29 |
| Rock Springs | 5a | May 31 | June 9 | Sep. 18 |
| Sheridan | 5a | May 24 | June 2 | Sep. 18 |
| Evanston | 5a | Any month | Any month | Any month |
| Riverton | 5a | May 18 | May 26 | Sep. 19 |
| Jackson | 4b | Any month | Any month | Any month |
| Cody | 5a | May 22 | June 1 | Sep. 20 |
Frost dates vary a lot across Wyoming. Among the cities above, Casper has the earliest last frost (around May 16) and Laramie the latest (around June 15), about 4 weeks apart. Elevation, nearby water and local terrain all make a difference, so use the dates for the place closest to you, or look up your ZIP code.
Growing zones in Wyoming
Most of Wyoming is in USDA hardiness zones 4b to 5b. A typical frost-free growing season lasts about 133 days, longer in the warmest areas and shorter in the coldest.
Find planting dates for the main zones in Wyoming:
- Zone 4 (about 26% of ZIP codes): Tomatoes, Peppers, Potatoes, Lettuce, Green beans, Cucumbers, Garlic, Tulips
- Zone 5 (about 73% of ZIP codes): Tomatoes, Peppers, Potatoes, Lettuce, Green beans, Cucumbers, Garlic, Tulips
See all crops in our planting guides, or build a planting calendar for your ZIP code.
How to use frost dates
- Cool-season crops such as peas, lettuce, spinach and onions can go in several weeks before your last spring frost.
- Warm-season crops such as tomatoes, peppers, squash and beans wait until after it, when the soil has warmed.
- Fall crops are timed back from your first fall frost, and garlic and tulips are planted around it.
- Frost dates are averages. Check the forecast before setting out tender plants.
Frequently asked questions
When is the last frost in Wyoming?
It depends on where you live. Across most of Wyoming, the last spring frost comes between May 15 and June 11. In Cheyenne, it is around May 20.
When is the first frost in Wyoming?
Across most of Wyoming, the first fall frost comes between September 3 and September 27. In Cheyenne, it is around September 26.
What planting zone is Wyoming?
Most of Wyoming is in USDA hardiness zones 4b to 5b. Enter your ZIP code above to find your exact zone.
When can I plant tomatoes in Wyoming?
Plant tomatoes outside after your last frost, once nights stay above 50 °F. In Cheyenne, the safer date, with only a 10% chance of a later frost, is around May 28. See when to plant tomatoes in zone 5.
Sources. Frost dates come from the nearest NOAA weather station to each city or ZIP code. Zones come from the 2023 USDA Plant Hardiness Zone Map ZIP code data. Our zone lookup is not the official USDA map.