Frost dates for Rock Springs, MT
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 15
typical year
Safe to plant
May 27
frost is over in 9 of 10 years
First fall frost
September 25
typical year
Growing season
132 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 | – | Apr 17 – May 1 | – |
| Spinach | – | Apr 3 – 24 | Jul 31 – Aug 14 |
| Lettuce | – | Apr 17 – May 8 | Jul 31 – Aug 14 |
| Radishes | – | Apr 17 – May 29 | Aug 14 – 28 |
| Onions | – | Apr 17 – May 1 | – |
| Potatoes | – | Apr 24 – May 8 | – |
| Carrots | – | Apr 24 – May 15 | Jul 3 – 17 |
| Beets | – | Apr 17 – May 1 | Jul 17 – 31 |
| Kale | Mar 6 – 20 | Apr 17 – May 1 | Jul 17 – 31 |
| Broccoli | Mar 6 – 20 | May 1 – 15 | Jul 17 – 31 |
| Cabbage | Feb 20 – Mar 6 | Apr 17 – May 1 | Jul 17 – 31 |
| Garlic | – | – | Aug 14 – Sep 4 |
| Warm-season crops | |||
| Tomatoes | Apr 1 – 15 | May 27 – Jun 10 | – |
| Peppers | Mar 25 – Apr 8 | Jun 3 – 17 | – |
| Cucumbers | – | May 27 – Jun 17 | – |
| Zucchini | – | May 27 – Jun 24 | – |
| Pumpkins | – | May 27 – Jun 17 | – |
| Green beans | – | May 27 – Jul 17 | – |
| Sweet corn | – | May 27 – Jun 24 | – |
| Basil | Apr 22 – May 6 | Jun 3 – 10 | – |
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 | May 27 | May 15 | May 2 |
| Fall frost before | September 10 | September 25 | October 6 |
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 5 (May 19 in a late year), and the first one in fall around October 3.
Where these dates come from
NOAA weather station ROCK SPRINGS, MT US (USC00247136), 1991–2020 climate normals. It's the nearest station for 1 zip code, all within 15 miles:
59312
Planting dates follow common university extension advice; your local extension service can fine-tune them for your soil and microclimate.