Last spring frost
May 18
Frost Dates for Coram, MT
First fall frost
Sep 20
Growing season
124 days
Hardiness zone
5a
In an average year around Coram, MT, the last spring frost (32°F) is about May 18 and the first fall frost is about Sep 20, giving roughly a 124-day growing season. To be safe most years, wait until May 6 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) | Jul 1 | Jun 8 | May 23 |
| Freeze (32°F) | Jun 4 | May 18 | May 6 |
| Hard (28°F) | May 15 | May 1 | Apr 18 |
| Severe (24°F) | Apr 28 | Apr 14 | Mar 31 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jul 1 | Jun 23 | Jun 16 | Jun 11 | Jun 8 | Jun 4 | Jun 1 | May 28 | May 23 |
| 32°F | Jun 4 | May 29 | May 24 | May 21 | May 18 | May 15 | May 13 | May 10 | May 6 |
| 28°F | May 15 | May 10 | May 7 | May 4 | May 1 | Apr 29 | Apr 27 | Apr 23 | Apr 18 |
| 24°F | Apr 28 | Apr 24 | Apr 21 | Apr 17 | Apr 14 | Apr 11 | Apr 7 | Apr 4 | Mar 31 |
| 20°F | Apr 17 | Apr 11 | Apr 6 | Apr 3 | Mar 31 | Mar 27 | Mar 23 | Mar 19 | Mar 12 |
| 16°F | Apr 3 | Mar 30 | Mar 26 | Mar 22 | Mar 18 | Mar 14 | Mar 10 | Mar 7 | Mar 2 |
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 19 | Sep 4 | Sep 20 |
| Freeze (32°F) | Sep 3 | Sep 20 | Oct 4 |
| Hard (28°F) | Sep 20 | Oct 4 | Oct 21 |
| Severe (24°F) | Oct 1 | Oct 19 | Nov 8 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 19 | Aug 25 | Aug 30 | Sep 1 | Sep 4 | Sep 7 | Sep 10 | Sep 15 | Sep 20 |
| 32°F | Sep 3 | Sep 9 | Sep 13 | Sep 17 | Sep 20 | Sep 23 | Sep 26 | Sep 30 | Oct 4 |
| 28°F | Sep 20 | Sep 26 | Sep 29 | Oct 1 | Oct 4 | Oct 7 | Oct 10 | Oct 15 | Oct 21 |
| 24°F | Oct 1 | Oct 6 | Oct 10 | Oct 15 | Oct 19 | Oct 24 | Oct 28 | Nov 1 | Nov 8 |
| 20°F | Oct 12 | Oct 19 | Oct 26 | Oct 30 | Nov 2 | Nov 6 | Nov 11 | Nov 16 | Nov 23 |
| 16°F | Oct 22 | Oct 30 | Nov 3 | Nov 8 | Nov 12 | Nov 17 | Nov 22 | Nov 27 | Dec 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: W Glacier, Mt, about 4.8 miles away@if(!empty($station['elevation_ft'])), at 3,148 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 Coram, MT?
On average, the last spring frost (32°F) around Coram, MT is about May 18. In cooler years it can run later, so for a safer bet many gardeners wait until May 6.
When is the first frost in the fall?
The first fall frost around Coram, MT typically arrives about Sep 20. 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 18 on average, or May 6 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 124 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 59913 Planting calendar → Montana frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026