Last spring frost
Jun 15
Frost Dates for Hebgen Lake Estates, MT
First fall frost
Sep 10
Growing season
87 days
Hardiness zone
4b
In an average year around Hebgen Lake Estates, MT, the last spring frost (32°F) is about Jun 15 and the first fall frost is about Sep 10, giving roughly a 87-day growing season. To be safe most years, wait until May 29 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 7 | Jun 15 | May 29 |
| Hard (28°F) | Jun 16 | May 24 | May 8 |
| Severe (24°F) | May 27 | May 7 | Apr 27 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 32°F | Jul 7 | Jun 30 | Jun 23 | Jun 19 | Jun 15 | Jun 11 | Jun 7 | Jun 4 | May 29 |
| 28°F | Jun 16 | Jun 7 | Jun 1 | May 27 | May 24 | May 20 | May 16 | May 12 | May 8 |
| 24°F | May 27 | May 17 | May 13 | May 10 | May 7 | May 5 | May 3 | May 1 | Apr 27 |
| 20°F | May 10 | May 6 | May 4 | May 1 | Apr 29 | Apr 26 | Apr 23 | Apr 19 | Apr 15 |
| 16°F | May 4 | Apr 29 | Apr 26 | Apr 22 | Apr 20 | Apr 17 | Apr 13 | Apr 10 | Apr 6 |
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 25 | Sep 10 | Sep 27 |
| Hard (28°F) | Sep 10 | Sep 26 | Oct 10 |
| Severe (24°F) | Sep 20 | Oct 7 | Oct 24 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 32°F | Aug 25 | Sep 1 | Sep 3 | Sep 6 | Sep 10 | Sep 13 | Sep 16 | Sep 20 | Sep 27 |
| 28°F | Sep 10 | Sep 15 | Sep 19 | Sep 23 | Sep 26 | Sep 29 | Oct 2 | Oct 5 | Oct 10 |
| 24°F | Sep 20 | Sep 27 | Oct 1 | Oct 4 | Oct 7 | Oct 11 | Oct 15 | Oct 19 | Oct 24 |
| 20°F | Oct 2 | Oct 6 | Oct 12 | Oct 16 | Oct 20 | Oct 23 | Oct 27 | Nov 1 | Nov 5 |
| 16°F | Oct 11 | Oct 18 | Oct 22 | Oct 26 | Oct 29 | Nov 1 | Nov 4 | Nov 8 | Nov 13 |
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: Hebgen Dam, Mt, about 8.6 miles away@if(!empty($station['elevation_ft'])), at 6,489 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 Hebgen Lake Estates, MT?
On average, the last spring frost (32°F) around Hebgen Lake Estates, MT is about Jun 15. In cooler years it can run later, so for a safer bet many gardeners wait until May 29.
When is the first frost in the fall?
The first fall frost around Hebgen Lake Estates, MT typically arrives about Sep 10. 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 15 on average, or May 29 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 87 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 59758 Planting calendar → Montana frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026