Last spring frost
May 25
Frost Dates for Ashland, MT
First fall frost
Sep 19
Growing season
115 days
Hardiness zone
4b
In an average year around Ashland, MT, the last spring frost (32°F) is about May 25 and the first fall frost is about Sep 19, giving roughly a 115-day growing season. To be safe most years, wait until May 12 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 27 | Jun 7 | May 23 |
| Freeze (32°F) | Jun 7 | May 25 | May 12 |
| Hard (28°F) | May 27 | May 14 | May 2 |
| Severe (24°F) | May 18 | May 2 | Apr 19 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 27 | Jun 19 | Jun 15 | Jun 11 | Jun 7 | Jun 4 | Jun 1 | May 28 | May 23 |
| 32°F | Jun 7 | Jun 3 | May 31 | May 27 | May 25 | May 22 | May 19 | May 16 | May 12 |
| 28°F | May 27 | May 23 | May 19 | May 16 | May 14 | May 11 | May 9 | May 6 | May 2 |
| 24°F | May 18 | May 12 | May 8 | May 5 | May 2 | Apr 30 | Apr 28 | Apr 24 | Apr 19 |
| 20°F | May 8 | May 2 | Apr 29 | Apr 25 | Apr 22 | Apr 19 | Apr 15 | Apr 11 | Apr 6 |
| 16°F | Apr 30 | Apr 24 | Apr 19 | Apr 15 | Apr 12 | Apr 8 | Apr 5 | Mar 31 | Mar 22 |
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 18 | Sep 6 | Sep 20 |
| Freeze (32°F) | Sep 1 | Sep 19 | Oct 1 |
| Hard (28°F) | Sep 14 | Sep 29 | Oct 12 |
| Severe (24°F) | Sep 23 | Oct 6 | Oct 21 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 18 | Aug 26 | Aug 31 | Sep 3 | Sep 6 | Sep 9 | Sep 13 | Sep 16 | Sep 20 |
| 32°F | Sep 1 | Sep 7 | Sep 12 | Sep 16 | Sep 19 | Sep 22 | Sep 24 | Sep 27 | Oct 1 |
| 28°F | Sep 14 | Sep 20 | Sep 23 | Sep 26 | Sep 29 | Oct 1 | Oct 4 | Oct 7 | Oct 12 |
| 24°F | Sep 23 | Sep 28 | Oct 1 | Oct 4 | Oct 6 | Oct 10 | Oct 13 | Oct 16 | Oct 21 |
| 20°F | Oct 1 | Oct 5 | Oct 9 | Oct 13 | Oct 16 | Oct 19 | Oct 22 | Oct 26 | Oct 30 |
| 16°F | Oct 6 | Oct 12 | Oct 17 | Oct 20 | Oct 24 | Oct 27 | Oct 30 | Nov 2 | Nov 8 |
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: Sonnette 7 Sw, Mt, about 18.1 miles away@if(!empty($station['elevation_ft'])), at 3,914 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 Ashland, MT?
On average, the last spring frost (32°F) around Ashland, MT is about May 25. In cooler years it can run later, so for a safer bet many gardeners wait until May 12.
When is the first frost in the fall?
The first fall frost around Ashland, MT typically arrives about Sep 19. 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 25 on average, or May 12 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 115 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 59003 Planting calendar → Montana frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026