Frost dates for Yellowstone Park Mammoth, 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
June 3
typical year
Safe to plant
June 19
frost is over in 9 of 10 years
First fall frost
September 14
typical year
Growing season
102 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 6 – 20 | – |
| Spinach | – | Apr 22 – May 13 | Jul 20 – Aug 3 |
| Lettuce | – | May 6 – 27 | Jul 20 – Aug 3 |
| Radishes | – | May 6 – Jun 17 | Aug 3 – 17 |
| Onions | – | May 6 – 20 | – |
| Potatoes | Season usually too short. Try a quick variety or row covers. | ||
| Carrots | – | May 13 – Jun 3 | Jun 22 – Jul 6 |
| Beets | – | May 6 – 20 | Jul 6 – 20 |
| Kale | Mar 25 – Apr 8 | May 6 – 20 | Jul 6 – 20 |
| Broccoli | Mar 25 – Apr 8 | May 20 – Jun 3 | Jul 6 – 20 |
| Cabbage | Mar 11 – 25 | May 6 – 20 | Jul 6 – 20 |
| Garlic | – | – | Aug 3 – 24 |
| 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 6 | – |
| 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 | June 3 | May 18 |
| Fall frost before | August 31 | September 14 | September 30 |
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 16 (May 30 in a late year), and the first one in fall around September 29.
Where these dates come from
NOAA weather station YELLOWSTONE PARK MAMMOTH, WY US (USC00489905), 1991–2020 climate normals. It's the nearest station for 1 zip code, all within 32 miles:
82190
1 of these zip codes are more than 30 miles from the station, so their real frost dates may differ by a week or more.
Planting dates follow common university extension advice; your local extension service can fine-tune them for your soil and microclimate.