Frost dates for St. Mary, 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 3
typical year
Safe to plant
June 23
frost is over in 9 of 10 years
First fall frost
September 8
typical year
Growing season
94 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 14 – 28 |
| Lettuce | – | May 6 – 27 | Jul 14 – 28 |
| Radishes | – | May 6 – Jun 17 | Jul 28 – Aug 11 |
| Onions | – | May 6 – 20 | – |
| Potatoes | Season usually too short. Try a quick variety or row covers. | ||
| Carrots | – | May 13 – Jun 3 | Jun 16 – 30 |
| Beets | – | May 6 – 20 | Jun 30 – Jul 14 |
| Kale | Mar 25 – Apr 8 | May 6 – 20 | Jun 30 – Jul 14 |
| Broccoli | Mar 25 – Apr 8 | May 20 – Jun 3 | Jun 30 – Jul 14 |
| Cabbage | Mar 11 – 25 | May 6 – 20 | Jun 30 – Jul 14 |
| Garlic | – | – | Jul 28 – Aug 18 |
| Warm-season crops | |||
| Tomatoes | Apr 28 – May 12 | Jun 23 – Jul 7 | – |
| Peppers | Season usually too short. Try a quick variety or row covers. | ||
| Cucumbers | – | Jun 23 – Jul 14 | – |
| Zucchini | – | Jun 23 – Jul 21 | – |
| Pumpkins | Season usually too short. Try a quick variety or row covers. | ||
| Green beans | – | Jun 23 – 30 | – |
| Sweet corn | Season usually too short. Try a quick variety or row covers. | ||
| Basil | May 19 – Jun 2 | Jun 30 – Jul 7 | – |
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 23 | June 3 | May 19 |
| Fall frost before | August 22 | September 8 | September 26 |
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 (May 28 in a late year), and the first one in fall around September 25.
Where these dates come from
NOAA weather station ST. MARY 1 SSW, MT US (USW00004130), 1991–2020 climate normals. It's the nearest station for 2 zip codes, all within 11 miles:
59411, 59434
Planting dates follow common university extension advice; your local extension service can fine-tune them for your soil and microclimate.