Frost dates for Blackleaf, 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 9
typical year
Safe to plant
July 2
frost is over in 9 of 10 years
First fall frost
September 3
typical year
Growing season
86 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 12 – 26 | – |
| Spinach | – | Apr 28 – May 19 | Jul 9 – 23 |
| Lettuce | – | May 12 – Jun 2 | Jul 9 – 23 |
| Radishes | – | May 12 – Jun 23 | Jul 23 – Aug 6 |
| Onions | – | May 12 – 26 | – |
| Potatoes | Season usually too short. Try a quick variety or row covers. | ||
| Carrots | – | May 19 – Jun 9 | Jun 11 – 25 |
| Beets | – | May 12 – 26 | Jun 25 – Jul 9 |
| Kale | Mar 31 – Apr 14 | May 12 – 26 | Jun 25 – Jul 9 |
| Broccoli | Mar 31 – Apr 14 | May 26 – Jun 9 | Jun 25 – Jul 9 |
| Cabbage | Mar 17 – 31 | May 12 – 26 | Jun 25 – Jul 9 |
| Garlic | – | – | Jul 23 – Aug 13 |
| Warm-season crops | |||
| Tomatoes | Season usually too short. Try a quick variety or row covers. | ||
| Peppers | Season usually too short. Try a quick variety or row covers. | ||
| Cucumbers | – | Jul 2 – 23 | – |
| Zucchini | – | Jul 2 – 30 | – |
| Pumpkins | Season usually too short. Try a quick variety or row covers. | ||
| Green beans | Season usually too short. Try a quick variety or row covers. | ||
| Sweet corn | Season usually too short. Try a quick variety or row covers. | ||
| Basil | May 28 – Jun 11 | Jul 9 – 16 | – |
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 | July 2 | June 9 | May 25 |
| Fall frost before | August 19 | September 3 | September 18 |
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 23 (June 6 in a late year), and the first one in fall around September 17.
Where these dates come from
NOAA weather station BLACKLEAF, MT US (USC00240877), 1991–2020 climate normals. It's the nearest station for 2 zip codes, all within 11 miles:
59432, 59467
Planting dates follow common university extension advice; your local extension service can fine-tune them for your soil and microclimate.