Last spring frost
May 25
Frost Dates for Plentywood, MT
First fall frost
Sep 14
Growing season
111 days
Hardiness zone
3b
In an average year around Plentywood, MT, the last spring frost (32°F) is about May 25 and the first fall frost is about Sep 14, giving roughly a 111-day growing season. To be safe most years, wait until May 13 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 29 | Jun 6 | May 23 |
| Freeze (32°F) | Jun 8 | May 25 | May 13 |
| Hard (28°F) | May 28 | May 15 | May 3 |
| Severe (24°F) | May 19 | May 6 | Apr 23 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 29 | Jun 22 | Jun 16 | Jun 10 | Jun 6 | Jun 2 | May 31 | May 28 | May 23 |
| 32°F | Jun 8 | Jun 2 | May 30 | May 27 | May 25 | May 22 | May 20 | May 17 | May 13 |
| 28°F | May 28 | May 24 | May 21 | May 18 | May 15 | May 13 | May 10 | May 7 | May 3 |
| 24°F | May 19 | May 15 | May 12 | May 8 | May 6 | May 4 | May 1 | Apr 29 | Apr 23 |
| 20°F | May 11 | May 5 | May 1 | Apr 29 | Apr 26 | Apr 22 | Apr 19 | Apr 16 | Apr 11 |
| 16°F | May 1 | Apr 27 | Apr 22 | Apr 18 | Apr 14 | Apr 11 | Apr 7 | Apr 4 | 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%) |
|---|---|---|---|
| Light (36°F) | Aug 21 | Sep 4 | Sep 15 |
| Freeze (32°F) | Sep 2 | Sep 14 | Sep 25 |
| Hard (28°F) | Sep 9 | Sep 22 | Oct 3 |
| Severe (24°F) | Sep 16 | Sep 29 | Oct 13 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 21 | Aug 28 | Aug 31 | Sep 2 | Sep 4 | Sep 6 | Sep 9 | Sep 12 | Sep 15 |
| 32°F | Sep 2 | Sep 5 | Sep 9 | Sep 11 | Sep 14 | Sep 16 | Sep 18 | Sep 21 | Sep 25 |
| 28°F | Sep 9 | Sep 14 | Sep 17 | Sep 20 | Sep 22 | Sep 24 | Sep 26 | Sep 29 | Oct 3 |
| 24°F | Sep 16 | Sep 20 | Sep 24 | Sep 27 | Sep 29 | Oct 2 | Oct 4 | Oct 8 | Oct 13 |
| 20°F | Sep 23 | Sep 28 | Oct 2 | Oct 5 | Oct 8 | Oct 11 | Oct 14 | Oct 19 | Oct 24 |
| 16°F | Oct 1 | Oct 7 | Oct 11 | Oct 15 | Oct 18 | Oct 21 | Oct 25 | Oct 29 | 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: Plentywood, Mt, about 3.7 miles away@if(!empty($station['elevation_ft'])), at 2,048 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 Plentywood, MT?
On average, the last spring frost (32°F) around Plentywood, MT is about May 25. In cooler years it can run later, so for a safer bet many gardeners wait until May 13.
When is the first frost in the fall?
The first fall frost around Plentywood, MT typically arrives about Sep 14. 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 25 on average, or May 13 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 111 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 59254 Planting calendar → Montana frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026