Frost dates for Boulder, 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
June 7
typical year
Safe to plant
June 25
frost is over in 9 of 10 years
First fall frost
September 8
typical year
Growing season
90 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 10 – 24 | – |
| Spinach | – | Apr 26 – May 17 | Jul 14 – 28 |
| Lettuce | – | May 10 – 31 | Jul 14 – 28 |
| Radishes | – | May 10 – Jun 21 | Jul 28 – Aug 11 |
| Onions | – | May 10 – 24 | – |
| Potatoes | Season usually too short. Try a quick variety or row covers. | ||
| Carrots | – | May 17 – Jun 7 | Jun 16 – 30 |
| Beets | – | May 10 – 24 | Jun 30 – Jul 14 |
| Kale | Mar 29 – Apr 12 | May 10 – 24 | Jun 30 – Jul 14 |
| Broccoli | Mar 29 – Apr 12 | May 24 – Jun 7 | Jun 30 – Jul 14 |
| Cabbage | Mar 15 – 29 | May 10 – 24 | Jun 30 – Jul 14 |
| Garlic | – | – | Jul 28 – Aug 18 |
| Warm-season crops | |||
| Tomatoes | Apr 30 – May 14 | Jun 25 – Jul 9 | – |
| Peppers | Season usually too short. Try a quick variety or row covers. | ||
| Cucumbers | – | Jun 25 – Jul 16 | – |
| Zucchini | – | Jun 25 – Jul 23 | – |
| Pumpkins | Season usually too short. Try a quick variety or row covers. | ||
| Green beans | – | Jun 25 – 30 | – |
| Sweet corn | Season usually too short. Try a quick variety or row covers. | ||
| Basil | May 21 – Jun 4 | Jul 2 – 9 | – |
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 25 | June 7 | May 24 |
| Fall frost before | August 25 | September 8 | September 21 |
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 21 (June 5 in a late year), and the first one in fall around September 21.
Towns that use these dates
This is the nearest NOAA station with frost records for 1 town.
Boulder
Where these dates come from
NOAA weather station BOULDER, MT US (USC00241008), 1991–2020 climate normals. It's the nearest station for 2 zip codes, all within 14 miles:
59631, 59632
Planting dates follow common university extension advice; your local extension service can fine-tune them for your soil and microclimate.