Frost dates for Mystic Lake, 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 5
typical year
Safe to plant
June 21
frost is over in 9 of 10 years
First fall frost
September 14
typical year
Growing season
99 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 8 – 22 | – |
| Spinach | – | Apr 24 – May 15 | Jul 20 – Aug 3 |
| Lettuce | – | May 8 – 29 | Jul 20 – Aug 3 |
| Radishes | – | May 8 – Jun 19 | Aug 3 – 17 |
| Onions | – | May 8 – 22 | – |
| Potatoes | Season usually too short. Try a quick variety or row covers. | ||
| Carrots | – | May 15 – Jun 5 | Jun 22 – Jul 6 |
| Beets | – | May 8 – 22 | Jul 6 – 20 |
| Kale | Mar 27 – Apr 10 | May 8 – 22 | Jul 6 – 20 |
| Broccoli | Mar 27 – Apr 10 | May 22 – Jun 5 | Jul 6 – 20 |
| Cabbage | Mar 13 – 27 | May 8 – 22 | Jul 6 – 20 |
| Garlic | – | – | Aug 3 – 24 |
| Warm-season crops | |||
| Tomatoes | Apr 26 – May 10 | Jun 21 – Jul 5 | – |
| Peppers | Apr 19 – May 3 | Jun 28 – Jul 12 | – |
| Cucumbers | – | Jun 21 – Jul 12 | – |
| Zucchini | – | Jun 21 – Jul 19 | – |
| Pumpkins | Season usually too short. Try a quick variety or row covers. | ||
| Green beans | – | Jun 21 – Jul 6 | – |
| Sweet corn | – | Jun 21 – Jul 19 | – |
| Basil | May 17 – 31 | Jun 28 – Jul 5 | – |
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 21 | June 5 | May 22 |
| Fall frost before | August 31 | September 14 | September 28 |
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 24 (June 11 in a late year), and the first one in fall around September 25.
Where these dates come from
NOAA weather station MYSTIC LAKE, MT US (USC00245961), 1991–2020 climate normals. It's the nearest station for 5 zip codes, all within 20 miles:
59020, 59028, 59068, 59071, 59081
Planting dates follow common university extension advice; your local extension service can fine-tune them for your soil and microclimate.