Growing season
72 days
Frost Dates for Grant, MT
Hardiness zone
5a
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 17 | May 30 | May 12 |
| Severe (24°F) | May 30 | May 10 | Apr 28 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 28°F | Jun 17 | Jun 12 | Jun 7 | Jun 2 | May 30 | May 25 | May 21 | May 17 | May 12 |
| 24°F | May 30 | May 22 | May 18 | May 13 | May 10 | May 8 | May 5 | May 2 | Apr 28 |
| 20°F | May 13 | May 8 | May 4 | May 1 | Apr 29 | Apr 26 | Apr 22 | Apr 17 | Apr 13 |
| 16°F | May 1 | Apr 26 | Apr 21 | Apr 16 | Apr 13 | Apr 9 | Apr 6 | Apr 2 | Mar 28 |
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) | Sep 1 | Sep 14 | Sep 28 |
| Severe (24°F) | Sep 11 | Sep 28 | Oct 12 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 28°F | Sep 1 | Sep 4 | Sep 8 | Sep 11 | Sep 14 | Sep 17 | Sep 20 | Sep 23 | Sep 28 |
| 24°F | Sep 11 | Sep 17 | Sep 21 | Sep 24 | Sep 28 | Sep 30 | Oct 2 | Oct 6 | Oct 12 |
| 20°F | Sep 24 | Sep 30 | Oct 3 | Oct 5 | Oct 9 | Oct 12 | Oct 15 | Oct 19 | Oct 23 |
| 16°F | Oct 4 | Oct 11 | Oct 15 | Oct 18 | Oct 21 | Oct 24 | Oct 27 | Oct 30 | Nov 3 |
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: Dillon 18 Wsw, Mt, about 10.2 miles away@if(!empty($station['elevation_ft'])), at 5,971 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 72 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 59725 Planting calendar → Montana frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026