Frost dates for Chinook, 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 23
typical year
Safe to plant
June 3
frost is over in 9 of 10 years
First fall frost
September 23
typical year
Growing season
121 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 25 – May 9 | – |
| Spinach | – | Apr 11 – May 2 | Jul 29 – Aug 12 |
| Lettuce | – | Apr 25 – May 16 | Jul 29 – Aug 12 |
| Radishes | – | Apr 25 – Jun 6 | Aug 12 – 26 |
| Onions | – | Apr 25 – May 9 | – |
| Potatoes | – | May 2 – 16 | – |
| Carrots | – | May 2 – 23 | Jul 1 – 15 |
| Beets | – | Apr 25 – May 9 | Jul 15 – 29 |
| Kale | Mar 14 – 28 | Apr 25 – May 9 | Jul 15 – 29 |
| Broccoli | Mar 14 – 28 | May 9 – 23 | Jul 15 – 29 |
| Cabbage | Feb 28 – Mar 14 | Apr 25 – May 9 | Jul 15 – 29 |
| Garlic | – | – | Aug 12 – Sep 2 |
| Warm-season crops | |||
| Tomatoes | Apr 8 – 22 | Jun 3 – 17 | – |
| Peppers | Apr 1 – 15 | Jun 10 – 24 | – |
| Cucumbers | – | Jun 3 – 24 | – |
| Zucchini | – | Jun 3 – Jul 1 | – |
| Pumpkins | – | Jun 3 – 24 | – |
| Green beans | – | Jun 3 – Jul 15 | – |
| Sweet corn | – | Jun 3 – Jul 1 | – |
| Basil | Apr 29 – May 13 | Jun 10 – 17 | – |
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 3 | May 23 | May 11 |
| Fall frost before | September 11 | September 23 | October 3 |
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 11 (May 24 in a late year), and the first one in fall around September 30.
Where these dates come from
NOAA weather station CHINOOK 35SE, MT US (USC00241730), 1991–2020 climate normals. It's the nearest station for 2 zip codes, all within 20 miles:
59527, 59535
Planting dates follow common university extension advice; your local extension service can fine-tune them for your soil and microclimate.