Last spring frost
May 14
Frost Dates for Sylvanite, MT
First fall frost
Sep 25
Growing season
132 days
Hardiness zone
6a
In an average year around Sylvanite, MT, the last spring frost (32°F) is about May 14 and the first fall frost is about Sep 25, giving roughly a 132-day growing season. To be safe most years, wait until Apr 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%) |
|---|---|---|---|
| Light (36°F) | Jun 27 | Jun 2 | May 18 |
| Freeze (32°F) | May 31 | May 14 | Apr 29 |
| Hard (28°F) | May 14 | Apr 29 | Apr 14 |
| Severe (24°F) | Apr 29 | Apr 8 | Mar 19 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 27 | Jun 15 | Jun 9 | Jun 5 | Jun 2 | May 30 | May 27 | May 23 | May 18 |
| 32°F | May 31 | May 25 | May 21 | May 17 | May 14 | May 11 | May 8 | May 4 | Apr 29 |
| 28°F | May 14 | May 8 | May 4 | May 1 | Apr 29 | Apr 27 | Apr 24 | Apr 19 | Apr 14 |
| 24°F | Apr 29 | Apr 22 | Apr 17 | Apr 12 | Apr 8 | Apr 5 | Apr 1 | Mar 28 | Mar 19 |
| 20°F | Apr 9 | Apr 3 | Mar 30 | Mar 25 | Mar 20 | Mar 15 | Mar 10 | Mar 6 | Feb 28 |
| 16°F | Mar 23 | Mar 15 | Mar 11 | Mar 7 | Mar 4 | Mar 1 | Feb 25 | Feb 20 | Feb 11 |
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 24 | Sep 7 | Sep 24 |
| Freeze (32°F) | Sep 9 | Sep 25 | Oct 9 |
| Hard (28°F) | Sep 21 | Oct 6 | Oct 30 |
| Severe (24°F) | Oct 1 | Oct 24 | Nov 16 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 24 | Aug 31 | Sep 2 | Sep 5 | Sep 7 | Sep 10 | Sep 14 | Sep 19 | Sep 24 |
| 32°F | Sep 9 | Sep 14 | Sep 18 | Sep 22 | Sep 25 | Sep 27 | Oct 1 | Oct 4 | Oct 9 |
| 28°F | Sep 21 | Sep 28 | Oct 1 | Oct 3 | Oct 6 | Oct 11 | Oct 16 | Oct 21 | Oct 30 |
| 24°F | Oct 1 | Oct 8 | Oct 14 | Oct 19 | Oct 24 | Oct 29 | Nov 3 | Nov 8 | Nov 16 |
| 20°F | Oct 13 | Oct 21 | Oct 28 | Nov 2 | Nov 8 | Nov 12 | Nov 19 | Nov 25 | Dec 2 |
| 16°F | Oct 25 | Nov 2 | Nov 10 | Nov 16 | Nov 22 | Nov 27 | Dec 2 | Dec 10 | Dec 22 |
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: Troy, Mt, about 12.1 miles away@if(!empty($station['elevation_ft'])), at 1,929 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 Sylvanite, MT?
On average, the last spring frost (32°F) around Sylvanite, MT is about May 14. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 29.
When is the first frost in the fall?
The first fall frost around Sylvanite, MT typically arrives about Sep 25. 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 14 on average, or Apr 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 132 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 59935 Planting calendar → Montana frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026