Last spring frost
May 11
Frost Dates for Indian Springs, MT
First fall frost
Sep 27
Growing season
138 days
Hardiness zone
5a
In an average year around Indian Springs, MT, the last spring frost (32°F) is about May 11 and the first fall frost is about Sep 27, giving roughly a 138-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 8 | May 26 | May 12 |
| Freeze (32°F) | May 25 | May 11 | Apr 28 |
| Hard (28°F) | May 12 | Apr 28 | Apr 10 |
| Severe (24°F) | Apr 30 | Apr 10 | Mar 23 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 8 | Jun 3 | Jun 1 | May 29 | May 26 | May 24 | May 21 | May 18 | May 12 |
| 32°F | May 25 | May 21 | May 17 | May 14 | May 11 | May 8 | May 5 | May 2 | Apr 28 |
| 28°F | May 12 | May 7 | May 4 | May 1 | Apr 28 | Apr 25 | Apr 22 | Apr 16 | Apr 10 |
| 24°F | Apr 30 | Apr 23 | Apr 18 | Apr 14 | Apr 10 | Apr 7 | Apr 3 | Mar 31 | Mar 23 |
| 20°F | Apr 12 | Apr 4 | Mar 31 | Mar 29 | Mar 25 | Mar 21 | Mar 16 | Mar 11 | Mar 6 |
| 16°F | Mar 28 | Mar 22 | Mar 17 | Mar 13 | Mar 9 | Mar 6 | Mar 3 | Feb 28 | Feb 21 |
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 28 | Sep 13 | Sep 30 |
| Freeze (32°F) | Sep 10 | Sep 27 | Oct 9 |
| Hard (28°F) | Sep 26 | Oct 7 | Oct 26 |
| Severe (24°F) | Oct 4 | Oct 20 | Nov 7 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 28 | Sep 2 | Sep 6 | Sep 9 | Sep 13 | Sep 16 | Sep 20 | Sep 24 | Sep 30 |
| 32°F | Sep 10 | Sep 17 | Sep 21 | Sep 24 | Sep 27 | Sep 29 | Oct 1 | Oct 5 | Oct 9 |
| 28°F | Sep 26 | Sep 30 | Oct 3 | Oct 5 | Oct 7 | Oct 11 | Oct 15 | Oct 18 | Oct 26 |
| 24°F | Oct 4 | Oct 8 | Oct 13 | Oct 17 | Oct 20 | Oct 24 | Oct 28 | Nov 1 | Nov 7 |
| 20°F | Oct 13 | Oct 20 | Oct 25 | Oct 29 | Nov 2 | Nov 5 | Nov 9 | Nov 14 | Nov 22 |
| 16°F | Oct 23 | Oct 30 | Nov 3 | Nov 8 | Nov 12 | Nov 16 | Nov 21 | Nov 26 | Dec 4 |
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: Eureka Rs, Mt, about 8.9 miles away@if(!empty($station['elevation_ft'])), at 2,532 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 Indian Springs, MT?
On average, the last spring frost (32°F) around Indian Springs, MT is about May 11. 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 Indian Springs, MT typically arrives about Sep 27. 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 11 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 138 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 59917 Planting calendar → Montana frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026