Last spring frost
Jun 10
Frost Dates for Butte-Silver Bow (balance), MT
First fall frost
Sep 7
Growing season
85 days
Hardiness zone
5a
In an average year around Butte-Silver Bow (balance), MT, the last spring frost (32°F) is about Jun 10 and the first fall frost is about Sep 7, giving roughly a 85-day growing season. To be safe most years, wait until May 23 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%) |
|---|---|---|---|
| Freeze (32°F) | Jul 2 | Jun 10 | May 23 |
| Hard (28°F) | Jun 9 | May 21 | May 6 |
| Severe (24°F) | May 21 | May 7 | Apr 22 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 32°F | Jul 2 | Jun 23 | Jun 18 | Jun 14 | Jun 10 | Jun 7 | Jun 2 | May 30 | May 23 |
| 28°F | Jun 9 | Jun 1 | May 28 | May 24 | May 21 | May 18 | May 14 | May 11 | May 6 |
| 24°F | May 21 | May 16 | May 13 | May 10 | May 7 | May 4 | May 1 | Apr 28 | Apr 22 |
| 20°F | May 13 | May 7 | May 3 | Apr 30 | Apr 26 | Apr 22 | Apr 19 | Apr 15 | Apr 9 |
| 16°F | May 1 | Apr 25 | Apr 20 | Apr 16 | Apr 12 | Apr 7 | Apr 3 | Mar 31 | Mar 23 |
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%) |
|---|---|---|---|
| Freeze (32°F) | Aug 24 | Sep 7 | Sep 20 |
| Hard (28°F) | Sep 3 | Sep 19 | Oct 2 |
| Severe (24°F) | Sep 14 | Oct 1 | Oct 16 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 32°F | Aug 24 | Aug 29 | Sep 1 | Sep 4 | Sep 7 | Sep 9 | Sep 12 | Sep 16 | Sep 20 |
| 28°F | Sep 3 | Sep 9 | Sep 13 | Sep 16 | Sep 19 | Sep 22 | Sep 25 | Sep 28 | Oct 2 |
| 24°F | Sep 14 | Sep 21 | Sep 25 | Sep 29 | Oct 1 | Oct 4 | Oct 7 | Oct 10 | Oct 16 |
| 20°F | Sep 28 | Oct 1 | Oct 5 | Oct 8 | Oct 11 | Oct 15 | Oct 18 | Oct 21 | Oct 25 |
| 16°F | Oct 4 | Oct 10 | Oct 15 | Oct 18 | Oct 21 | Oct 25 | Oct 28 | Nov 1 | Nov 6 |
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: Divide, Mt, about 5 miles away@if(!empty($station['elevation_ft'])), at 5,350 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 Butte-Silver Bow (balance), MT?
On average, the last spring frost (32°F) around Butte-Silver Bow (balance), MT is about Jun 10. In cooler years it can run later, so for a safer bet many gardeners wait until May 23.
When is the first frost in the fall?
The first fall frost around Butte-Silver Bow (balance), MT typically arrives about Sep 7. 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 Jun 10 on average, or May 23 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 85 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 59727 Planting calendar → Montana frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026