Frost dates for Thermopolis, WY
When the last spring frost and first fall frost usually come, and when to plant, from 30 years of NOAA weather records.
Last spring frost
May 29
typical year
Safe to plant
June 19
frost is over in 9 of 10 years
First fall frost
September 17
typical year
Growing season
110 days
frost-free, typical year
Frost watch this week
Tonight's and the next six nights' lows from the National Weather Service forecast for the station's location. Frost: 32°F or colder. Possible frost: 33–36°F, mostly in low spots on clear, still nights.
When to plant
Counted from this page's frost dates. Warm-season crops wait for the safe-to-plant date.
| Crop | Start indoors | Plant outside | Fall planting |
|---|---|---|---|
| Cool-season crops | |||
| Peas | – | May 1 – 15 | – |
| Spinach | – | Apr 17 – May 8 | Jul 23 – Aug 6 |
| Lettuce | – | May 1 – 22 | Jul 23 – Aug 6 |
| Radishes | – | May 1 – Jun 12 | Aug 6 – 20 |
| Onions | – | May 1 – 15 | – |
| Potatoes | – | May 8 – 22 | – |
| Carrots | – | May 8 – 29 | Jun 25 – Jul 9 |
| Beets | – | May 1 – 15 | Jul 9 – 23 |
| Kale | Mar 20 – Apr 3 | May 1 – 15 | Jul 9 – 23 |
| Broccoli | Mar 20 – Apr 3 | May 15 – 29 | Jul 9 – 23 |
| Cabbage | Mar 6 – 20 | May 1 – 15 | Jul 9 – 23 |
| Garlic | – | – | Aug 6 – 27 |
| Warm-season crops | |||
| Tomatoes | Apr 24 – May 8 | Jun 19 – Jul 3 | – |
| Peppers | Apr 17 – May 1 | Jun 26 – Jul 10 | – |
| Cucumbers | – | Jun 19 – Jul 10 | – |
| Zucchini | – | Jun 19 – Jul 17 | – |
| Pumpkins | Season usually too short. Try a quick variety or row covers. | ||
| Green beans | – | Jun 19 – Jul 9 | – |
| Sweet corn | – | Jun 19 – Jul 17 | – |
| Basil | May 15 – 29 | Jun 26 – Jul 3 | – |
Onions: from sets. Green beans: until 10 weeks before the first fall frost. Garlic: harvest next summer.
The year at a glance
Start indoors Plant outside Fall planting
The chance of frost, by date
| 1 year in 10 | Half of years | 9 years in 10 | |
|---|---|---|---|
| Spring frost after | June 19 | May 29 | May 14 |
| Fall frost before | September 3 | September 17 | October 1 |
Frost here means 32°F or colder. Read across: in 1 year in 10, spring frost carries on past the first date, which is why that date is the safe-to-plant date.
Hard freeze (28°F)
A hard freeze kills most garden plants, even hardy ones. The last one in spring usually comes around May 14 (June 2 in a late year), and the first one in fall around September 29.
Where these dates come from
NOAA weather station THERMOPOLIS 21WNW, WY US (USC00488888), 1991–2020 climate normals. It's the nearest station for 1 zip code, all within 11 miles:
82443
Planting dates follow common university extension advice; your local extension service can fine-tune them for your soil and microclimate.