Last spring frost
May 22
Frost Dates for Clark Fork, ID
First fall frost
Sep 22
Growing season
122 days
Hardiness zone
6b
In an average year around Clark Fork, ID, the last spring frost (32°F) is about May 22 and the first fall frost is about Sep 22, giving roughly a 122-day growing season. To be safe most years, wait until May 5 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 7 | May 22 |
| Freeze (32°F) | Jun 6 | May 22 | May 5 |
| Hard (28°F) | May 23 | May 4 | Apr 12 |
| Severe (24°F) | May 6 | Apr 7 | Mar 17 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jul 1 | Jun 21 | Jun 15 | Jun 10 | Jun 7 | Jun 4 | Jun 1 | May 29 | May 22 |
| 32°F | Jun 6 | May 31 | May 28 | May 25 | May 22 | May 18 | May 14 | May 10 | May 5 |
| 28°F | May 23 | May 16 | May 12 | May 8 | May 4 | Apr 30 | Apr 26 | Apr 21 | Apr 12 |
| 24°F | May 6 | Apr 28 | Apr 20 | Apr 13 | Apr 7 | Apr 2 | Mar 30 | Mar 25 | Mar 17 |
| 20°F | Apr 7 | Mar 30 | Mar 23 | Mar 18 | Mar 14 | Mar 10 | Mar 7 | Mar 3 | Feb 25 |
| 16°F | Mar 17 | Mar 11 | Mar 6 | Mar 3 | Feb 28 | Feb 25 | Feb 20 | Feb 15 | Feb 5 |
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 20 | Sep 6 | Sep 23 |
| Freeze (32°F) | Sep 3 | Sep 22 | Oct 7 |
| Hard (28°F) | Sep 18 | Oct 4 | Oct 21 |
| Severe (24°F) | Oct 1 | Oct 20 | Nov 11 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 20 | Aug 28 | Sep 1 | Sep 3 | Sep 6 | Sep 10 | Sep 14 | Sep 18 | Sep 23 |
| 32°F | Sep 3 | Sep 10 | Sep 15 | Sep 19 | Sep 22 | Sep 26 | Sep 30 | Oct 3 | Oct 7 |
| 28°F | Sep 18 | Sep 25 | Sep 29 | Oct 2 | Oct 4 | Oct 7 | Oct 11 | Oct 16 | Oct 21 |
| 24°F | Oct 1 | Oct 6 | Oct 11 | Oct 16 | Oct 20 | Oct 25 | Oct 28 | Nov 2 | Nov 11 |
| 20°F | Oct 14 | Oct 22 | Oct 27 | Nov 1 | Nov 4 | Nov 9 | Nov 14 | Nov 20 | Nov 27 |
| 16°F | Oct 25 | Nov 1 | Nov 7 | Nov 13 | Nov 18 | Nov 23 | Nov 28 | Dec 4 | Dec 12 |
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: Bayview Model Basin, Id, about 9.1 miles away@if(!empty($station['elevation_ft'])), at 2,087 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 Clark Fork, ID?
On average, the last spring frost (32°F) around Clark Fork, ID is about May 22. In cooler years it can run later, so for a safer bet many gardeners wait until May 5.
When is the first frost in the fall?
The first fall frost around Clark Fork, ID typically arrives about Sep 22. 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 22 on average, or May 5 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 122 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 83803 Planting calendar → Idaho frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026