Thermopolis, WY frost dates
Last spring frostMay 24median date
First fall frostSep 16median date
Growing season115 daysfrost-free
Hardiness zone5aZone 5a
How Thermopolis compares
- In 8 years out of 10, the last spring frost in Thermopolis falls between May 12 and June 9, a 28-day window. The first fall frost falls between September 4 and September 29.
- The median last frost is 3 days later than the Wyoming median of May 21.
- Its 115-day growing season is longer than 25% of the 153 Wyoming places with a regular frost season (state median 125 days).
- The last frost is 21 days later than the zone 5a median of May 3. Hardiness zones measure winter cold, not season length, so use these dates rather than a zone 5a chart.
- The weather station records an average of 211 nights a year at or below 32°F.
Frost probability
| Chance of frost after | Date |
|---|---|
| 90% (early) | May 12 |
| 50% (median) | May 24 |
| 10% (safe for tender plants) | June 9 |
| Chance of frost before | Date |
|---|---|
| 10% (early) | September 4 |
| 50% (median) | September 16 |
| 90% (late) | September 29 |
Frost here means 32°F (0°C). A median date means half of years have their last frost earlier and half later.
Planting calendar for Thermopolis, WY
Thermopolis, WY frost dates — last frost May 24, first frost Sep 16, zone 5a. whenisthelastfrost.com
Crop
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Start indoors: Mar 1 to Mar 15Transplant outside: Apr 26 to May 10
Start indoors: Mar 15 to Mar 29Transplant outside: Jun 7 to Jun 21
Start indoors: Mar 15 to Mar 29Transplant outside: Jun 7 to Jun 21
Start indoors: Mar 29 to Apr 12Transplant outside: May 31 to Jun 14
Start indoors: Mar 29 to Apr 12Transplant outside: May 3 to May 17Sow outdoors: Apr 26 to May 31Plant for fall: Jul 22 to Aug 19
Start indoors: Mar 29 to Apr 12Transplant outside: Apr 26 to May 10Sow outdoors: Apr 26 to May 10Plant for fall: Jul 8 to Jul 29
Start indoors: Mar 29 to Apr 12Transplant outside: May 10 to May 24Plant for fall: Jun 10 to Jul 1
Start indoors: Mar 29 to Apr 12Transplant outside: May 3 to May 17Plant for fall: Jun 10 to Jul 1
Start indoors: Mar 29 to Apr 12Transplant outside: May 10 to May 24Plant for fall: Jun 10 to Jul 1
Start indoors: Apr 12 to Apr 26Transplant outside: Jun 14 to Jun 28Sow outdoors: Jun 14 to Jun 28
Start indoors: Apr 12 to Apr 26Transplant outside: May 31 to Jun 14
Sow outdoors: Apr 12 to May 3Plant for fall: Jun 24 to Jul 15
Sow outdoors: Apr 12 to May 3Plant for fall: Jul 22 to Aug 12
Sow outdoors: Apr 19 to May 31Plant for fall: Aug 5 to Aug 26
Start indoors: Apr 26 to May 3Transplant outside: Jun 7 to Jun 14Sow outdoors: May 31 to Jun 14Plant for fall: Jul 1 to Jul 15
Start indoors: Apr 26 to May 3Sow outdoors: May 31 to Jun 14Plant for fall: Jul 8 to Jul 22
Start indoors: Apr 26 to May 3Sow outdoors: May 31 to Jun 14
Start indoors: Apr 26 to May 3Transplant outside: Jun 7 to Jun 21
Sow outdoors: May 3 to May 31Plant for fall: Jun 24 to Jul 8
Sow outdoors: May 3 to May 31Plant for fall: Jul 8 to Jul 22
Sow outdoors: May 3 to May 24
Sow outdoors: May 10 to Jun 7Plant for fall: Jul 8 to Jul 22
Sow outdoors: May 10 to May 31Plant for fall: Jul 22 to Aug 12
Sow outdoors: May 31 to Jun 21
Sow outdoors: May 31 to Jun 14
Transplant outside: Jun 7 to Jun 28
Plant for fall: Sep 2 to Oct 7
Start indoorsTransplant outsideSow outdoorsPlant for fallMedian frost dates
When to plant vegetables in Thermopolis, WY
| Crop | Start indoors | Transplant | Sow outdoors | Fall crop |
|---|---|---|---|---|
| Onions | Mar 1 – Mar 15 | Apr 26 – May 10 | — | — |
| Peppers | Mar 15 – Mar 29 | Jun 7 – Jun 21 | — | — |
| Eggplant | Mar 15 – Mar 29 | Jun 7 – Jun 21 | — | — |
| Tomatoes | Mar 29 – Apr 12 | May 31 – Jun 14 | — | — |
| Lettuce | Mar 29 – Apr 12 | May 3 – May 17 | Apr 26 – May 31 | Jul 22 – Aug 19 |
| Kale | Mar 29 – Apr 12 | Apr 26 – May 10 | Apr 26 – May 10 | Jul 8 – Jul 29 |
| Broccoli | Mar 29 – Apr 12 | May 10 – May 24 | — | Jun 10 – Jul 1 |
| Cabbage | Mar 29 – Apr 12 | May 3 – May 17 | — | Jun 10 – Jul 1 |
| Cauliflower | Mar 29 – Apr 12 | May 10 – May 24 | — | Jun 10 – Jul 1 |
| Okra | Apr 12 – Apr 26 | Jun 14 – Jun 28 | Jun 14 – Jun 28 | — |
| Basil | Apr 12 – Apr 26 | May 31 – Jun 14 | — | — |
| Peas | — | — | Apr 12 – May 3 | Jun 24 – Jul 15 |
| Spinach | — | — | Apr 12 – May 3 | Jul 22 – Aug 12 |
| Radishes | — | — | Apr 19 – May 31 | Aug 5 – Aug 26 |
| Cucumbers | Apr 26 – May 3 | Jun 7 – Jun 14 | May 31 – Jun 14 | Jul 1 – Jul 15 |
| Zucchini & Summer Squash | Apr 26 – May 3 | — | May 31 – Jun 14 | Jul 8 – Jul 22 |
| Winter Squash & Pumpkins | Apr 26 – May 3 | — | May 31 – Jun 14 | — |
| Melons & Watermelon | Apr 26 – May 3 | Jun 7 – Jun 21 | — | — |
| Carrots | — | — | May 3 – May 31 | Jun 24 – Jul 8 |
| Beets | — | — | May 3 – May 31 | Jul 8 – Jul 22 |
| Potatoes | — | — | May 3 – May 24 | — |
| Swiss Chard | — | — | May 10 – Jun 7 | Jul 8 – Jul 22 |
| Cilantro | — | — | May 10 – May 31 | Jul 22 – Aug 12 |
| Green Beans | — | — | May 31 – Jun 21 | — |
| Sweet Corn | — | — | May 31 – Jun 14 | — |
| Sweet Potatoes | — | Jun 7 – Jun 28 | — | — |
| Garlic | — | — | — | Sep 2 – Oct 7 |
Dates come from the median frost dates and common extension-service timing. Adjust for your soil temperature, microclimate and the varieties you grow.
About these dates
Based on 1991–2020 NOAA climate normals for the Thermopolis 9ne, WY weather station, 20 km away (elevation 4,281 ft (1,305 m)).
Frost dates near Thermopolis
- Kirby May 24 · Sep 16
- Worland May 4 · Oct 1
- Pavillion May 14 · Sep 30
- Shoshoni May 7 · Oct 3
- Manderson Apr 28 · Oct 10
- Meeteetse frost any month
- Otto May 12 · Sep 28
- Kinnear May 21 · Sep 20
- Basin Apr 28 · Oct 10
- Burlington May 12 · Sep 28
Frequently asked questions
When is the last frost in Thermopolis, WY?
The median last spring frost in Thermopolis, WY is May 24. There is still about a 10% chance of frost after June 9, so wait until then to plant frost-tender crops like tomatoes and peppers.
When is the first frost in Thermopolis, WY?
The median first fall frost is September 16, with about a 10% chance of frost before September 4.
How long is the growing season in Thermopolis, WY?
About 115 days between the median last spring frost and first fall frost.
What planting zone is Thermopolis, WY?
Thermopolis, WY is in USDA hardiness zone 5a.