Last spring frost
May 31
Frost Dates for Mullan, ID
First fall frost
Sep 5
Growing season
95 days
Hardiness zone
6a
In an average year around Mullan, ID, the last spring frost (32°F) is about May 31 and the first fall frost is about Sep 5, giving roughly a 95-day growing season. To be safe most years, wait until May 16 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) | Jun 23 | May 31 | May 16 |
| Hard (28°F) | May 25 | May 11 | Apr 27 |
| Severe (24°F) | May 9 | Apr 23 | Mar 31 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 32°F | Jun 23 | Jun 12 | Jun 7 | Jun 4 | May 31 | May 28 | May 25 | May 21 | May 16 |
| 28°F | May 25 | May 19 | May 16 | May 14 | May 11 | May 8 | May 6 | May 2 | Apr 27 |
| 24°F | May 9 | May 4 | May 1 | Apr 28 | Apr 23 | Apr 19 | Apr 14 | Apr 8 | Mar 31 |
| 20°F | Apr 15 | Apr 6 | Apr 1 | Mar 29 | Mar 25 | Mar 21 | Mar 16 | Mar 12 | Mar 7 |
| 16°F | Mar 22 | Mar 17 | Mar 13 | Mar 10 | Mar 6 | Mar 3 | Feb 28 | Feb 21 | Feb 14 |
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 20 | Sep 5 | Sep 21 |
| Hard (28°F) | Sep 5 | Sep 24 | Oct 14 |
| Severe (24°F) | Sep 23 | Oct 16 | Nov 7 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 32°F | Aug 20 | Aug 26 | Aug 30 | Sep 2 | Sep 5 | Sep 7 | Sep 10 | Sep 15 | Sep 21 |
| 28°F | Sep 5 | Sep 10 | Sep 15 | Sep 19 | Sep 24 | Sep 27 | Oct 1 | Oct 6 | Oct 14 |
| 24°F | Sep 23 | Sep 29 | Oct 4 | Oct 10 | Oct 16 | Oct 20 | Oct 24 | Oct 29 | Nov 7 |
| 20°F | Oct 13 | Oct 22 | Oct 28 | Nov 2 | Nov 6 | Nov 11 | Nov 17 | Nov 24 | Dec 2 |
| 16°F | Oct 31 | Nov 5 | Nov 12 | Nov 19 | Nov 24 | Nov 28 | Dec 2 | Dec 8 | Dec 18 |
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: Prichard 3 Ese, Id, about 5.2 miles away@if(!empty($station['elevation_ft'])), at 2,547 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 Mullan, ID?
On average, the last spring frost (32°F) around Mullan, ID is about May 31. In cooler years it can run later, so for a safer bet many gardeners wait until May 16.
When is the first frost in the fall?
The first fall frost around Mullan, ID typically arrives about Sep 5. 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 31 on average, or May 16 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 95 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 83874 Planting calendar → Idaho frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026