Last spring frost
May 23
Frost Dates for Four Corners, MT
First fall frost
Sep 23
Growing season
123 days
Hardiness zone
5a
In an average year around Four Corners, MT, the last spring frost (32°F) is about May 23 and the first fall frost is about Sep 23, giving roughly a 123-day growing season. To be safe most years, wait until May 5 before setting out tender plants.
Last spring frost
Dates the last frost of spring typically ends. Plant tender crops after the risk has passed for your comfort level.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Light (36°F) | Jun 30 | Jun 13 | May 26 |
| Freeze (32°F) | Jun 12 | May 23 | May 5 |
| Hard (28°F) | May 18 | May 2 | Apr 20 |
| Severe (24°F) | May 6 | Apr 21 | Apr 4 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 30 | Jun 24 | Jun 20 | Jun 16 | Jun 13 | Jun 10 | Jun 6 | Jun 2 | May 26 |
| 32°F | Jun 12 | Jun 5 | May 31 | May 27 | May 23 | May 18 | May 15 | May 10 | May 5 |
| 28°F | May 18 | May 12 | May 8 | May 5 | May 2 | Apr 30 | Apr 28 | Apr 25 | Apr 20 |
| 24°F | May 6 | May 1 | Apr 28 | Apr 25 | Apr 21 | Apr 18 | Apr 14 | Apr 9 | Apr 4 |
| 20°F | Apr 26 | Apr 19 | Apr 14 | Apr 10 | Apr 7 | Apr 4 | Apr 2 | Mar 30 | Mar 21 |
| 16°F | Apr 14 | Apr 7 | Apr 4 | Apr 1 | Mar 29 | Mar 24 | Mar 20 | Mar 14 | Mar 8 |
First fall frost
Dates the first frost of fall typically arrives. Count back by a crop's days-to-maturity to know your planting cutoff.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Light (36°F) | Aug 22 | Sep 9 | Sep 24 |
| Freeze (32°F) | Sep 4 | Sep 23 | Oct 6 |
| Hard (28°F) | Sep 17 | Oct 3 | Oct 19 |
| Severe (24°F) | Sep 29 | Oct 16 | Nov 1 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 22 | Aug 29 | Sep 2 | Sep 5 | Sep 9 | Sep 13 | Sep 16 | Sep 20 | Sep 24 |
| 32°F | Sep 4 | Sep 12 | Sep 16 | Sep 20 | Sep 23 | Sep 26 | Sep 30 | Oct 2 | Oct 6 |
| 28°F | Sep 17 | Sep 24 | Sep 28 | Oct 1 | Oct 3 | Oct 6 | Oct 10 | Oct 14 | Oct 19 |
| 24°F | Sep 29 | Oct 4 | Oct 7 | Oct 12 | Oct 16 | Oct 19 | Oct 23 | Oct 28 | Nov 1 |
| 20°F | Oct 7 | Oct 14 | Oct 19 | Oct 23 | Oct 27 | Oct 30 | Nov 2 | Nov 5 | Nov 11 |
| 16°F | Oct 17 | Oct 23 | Oct 28 | Nov 1 | Nov 3 | Nov 6 | Nov 9 | Nov 13 | Nov 18 |
Growing season is measured at 32°F with about 50% probability. Hardiness zone from the 2023 USDA map; frost normals from NOAA 1991-2020.
Where this data comes from
@endif These dates are computed from the nearest official weather station with long-term records: Bozeman 6 W Exp Farm, Mt, about 2.4 miles away@if(!empty($station['elevation_ft'])), at 4,775 ft elevation. The further the station and the greater the elevation difference from your yard, the more your local frost timing can vary.
How we calculate these dates
Frost and freeze dates come from the NOAA 1991–2020 U.S. Climate Normals, the National Oceanic and Atmospheric Administration's 30-year averages for each weather station. A date shown at the 50% level is the median: in half of years the frost falls on or before it. The 10% and 90% columns show the early and late ends of the range, so you can plant on the odds you're comfortable with. These are long-term averages, not a forecast for this year - always check your local outlook before planting.
Source: NOAA National Centers for Environmental Information, 1991–2020 Climate Normals (public domain). Harman is not affiliated with or endorsed by NOAA.
Frequently asked questions
When is the last frost in Four Corners, MT?
On average, the last spring frost (32°F) around Four Corners, MT is about May 23. In cooler years it can run later, so for a safer bet many gardeners wait until May 5.
When is the first frost in the fall?
The first fall frost around Four Corners, MT typically arrives about Sep 23. Count back by a crop's days to maturity to find the latest date you can plant it.
When can I plant tomatoes and other tender crops?
Tender crops like tomatoes, peppers and basil are damaged by frost, so wait until the last spring frost has passed - around May 23 on average, or May 5 to be safe most years.
How long is the growing season here?
The frost-free growing season (between the last spring and first fall 32°F frost) is about 123 days in a typical year.
Are these dates a forecast for this year?
No. They are 30-year averages from the NOAA 1991–2020 Climate Normals, not a prediction for the current year. Use them for planning and always check your local weather forecast before planting or protecting crops.
Local weather for 59718 Planting calendar → Montana frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026