Growing season
71 days
Frost Dates for Glen, MT
Hardiness zone
4b
Frost normals for this location are limited (the nearest long-term weather station may not report all thresholds). The available data is shown below.
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%) |
|---|---|---|---|
| Hard (28°F) | Jun 16 | May 29 | May 15 |
| Severe (24°F) | May 29 | May 12 | May 1 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 28°F | Jun 16 | Jun 11 | Jun 6 | Jun 2 | May 29 | May 25 | May 22 | May 18 | May 15 |
| 24°F | May 29 | May 22 | May 17 | May 15 | May 12 | May 10 | May 7 | May 4 | May 1 |
| 20°F | May 13 | May 10 | May 7 | May 5 | May 3 | May 1 | Apr 27 | Apr 23 | Apr 16 |
| 16°F | May 4 | Apr 30 | Apr 26 | Apr 21 | Apr 18 | Apr 13 | Apr 9 | Apr 6 | Mar 31 |
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%) |
|---|---|---|---|
| Hard (28°F) | Aug 29 | Sep 10 | Sep 22 |
| Severe (24°F) | Sep 7 | Sep 22 | Oct 5 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 28°F | Aug 29 | Sep 1 | Sep 4 | Sep 7 | Sep 10 | Sep 12 | Sep 15 | Sep 19 | Sep 22 |
| 24°F | Sep 7 | Sep 12 | Sep 16 | Sep 19 | Sep 22 | Sep 24 | Sep 27 | Oct 1 | Oct 5 |
| 20°F | Sep 20 | Sep 25 | Sep 28 | Oct 1 | Oct 3 | Oct 5 | Oct 9 | Oct 14 | Oct 19 |
| 16°F | Sep 30 | Oct 3 | Oct 6 | Oct 10 | Oct 14 | Oct 18 | Oct 22 | Oct 26 | Oct 31 |
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: Glen 4 N, Mt, about 1.8 miles away@if(!empty($station['elevation_ft'])), at 5,054 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
How long is the growing season here?
The frost-free growing season (between the last spring and first fall 32°F frost) is about 71 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 59732 Planting calendar → Montana frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026