Last spring frost
May 10
Frost Dates for Musselshell, MT
First fall frost
Sep 29
Growing season
141 days
Hardiness zone
4b
In an average year around Musselshell, MT, the last spring frost (32°F) is about May 10 and the first fall frost is about Sep 29, giving roughly a 141-day growing season. To be safe most years, wait until Apr 28 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 3 | May 21 | May 9 |
| Freeze (32°F) | May 23 | May 10 | Apr 28 |
| Hard (28°F) | May 13 | Apr 29 | Apr 13 |
| Severe (24°F) | May 2 | Apr 16 | Mar 31 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 3 | May 30 | May 26 | May 23 | May 21 | May 19 | May 16 | May 13 | May 9 |
| 32°F | May 23 | May 19 | May 15 | May 12 | May 10 | May 7 | May 4 | May 2 | Apr 28 |
| 28°F | May 13 | May 8 | May 4 | May 1 | Apr 29 | Apr 26 | Apr 22 | Apr 18 | Apr 13 |
| 24°F | May 2 | Apr 27 | Apr 23 | Apr 20 | Apr 16 | Apr 12 | Apr 8 | Apr 4 | Mar 31 |
| 20°F | Apr 24 | Apr 19 | Apr 12 | Apr 8 | Apr 4 | Apr 1 | Mar 28 | Mar 22 | Mar 15 |
| 16°F | Apr 12 | Apr 6 | Apr 1 | Mar 30 | Mar 25 | Mar 20 | Mar 15 | Mar 10 | Mar 5 |
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) | Sep 5 | Sep 20 | Oct 2 |
| Freeze (32°F) | Sep 14 | Sep 29 | Oct 12 |
| Hard (28°F) | Sep 24 | Oct 7 | Oct 22 |
| Severe (24°F) | Sep 30 | Oct 17 | Oct 31 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 5 | Sep 10 | Sep 14 | Sep 17 | Sep 20 | Sep 22 | Sep 25 | Sep 28 | Oct 2 |
| 32°F | Sep 14 | Sep 20 | Sep 23 | Sep 26 | Sep 29 | Oct 1 | Oct 4 | Oct 7 | Oct 12 |
| 28°F | Sep 24 | Sep 28 | Oct 1 | Oct 5 | Oct 7 | Oct 10 | Oct 14 | Oct 17 | Oct 22 |
| 24°F | Sep 30 | Oct 5 | Oct 9 | Oct 14 | Oct 17 | Oct 20 | Oct 23 | Oct 27 | Oct 31 |
| 20°F | Oct 7 | Oct 15 | Oct 19 | Oct 23 | Oct 27 | Oct 31 | Nov 3 | Nov 7 | Nov 14 |
| 16°F | Oct 18 | Oct 24 | Oct 29 | Nov 2 | Nov 6 | Nov 9 | Nov 14 | Nov 18 | Nov 23 |
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: Melstone, Mt, about 11.5 miles away@if(!empty($station['elevation_ft'])), at 2,932 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 Musselshell, MT?
On average, the last spring frost (32°F) around Musselshell, MT is about May 10. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 28.
When is the first frost in the fall?
The first fall frost around Musselshell, MT typically arrives about Sep 29. 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 10 on average, or Apr 28 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 141 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 59059 Planting calendar → Montana frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026