Last spring frost
May 16
Frost Dates for Fernwood, ID
First fall frost
Sep 23
Growing season
128 days
Hardiness zone
6a
In an average year around Fernwood, ID, the last spring frost (32°F) is about May 16 and the first fall frost is about Sep 23, giving roughly a 128-day growing season. To be safe most years, wait until May 2 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 6 | Jun 6 | May 20 |
| Freeze (32°F) | Jun 1 | May 16 | May 2 |
| Hard (28°F) | May 14 | Apr 30 | Apr 15 |
| Severe (24°F) | Apr 27 | Apr 7 | Mar 17 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jul 6 | Jun 25 | Jun 17 | Jun 12 | Jun 6 | Jun 2 | May 30 | May 27 | May 20 |
| 32°F | Jun 1 | May 27 | May 22 | May 19 | May 16 | May 13 | May 10 | May 7 | May 2 |
| 28°F | May 14 | May 10 | May 6 | May 2 | Apr 30 | Apr 28 | Apr 25 | Apr 21 | Apr 15 |
| 24°F | Apr 27 | Apr 21 | Apr 17 | Apr 12 | Apr 7 | Apr 4 | Mar 31 | Mar 25 | Mar 17 |
| 20°F | Apr 6 | Mar 31 | Mar 24 | Mar 20 | Mar 16 | Mar 12 | Mar 8 | Mar 4 | Feb 28 |
| 16°F | Mar 21 | Mar 15 | Mar 10 | Mar 6 | Mar 3 | Feb 28 | Feb 25 | Feb 19 | Feb 13 |
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 27 | Sep 10 | Sep 25 |
| Freeze (32°F) | Sep 6 | Sep 23 | Oct 9 |
| Hard (28°F) | Sep 20 | Oct 8 | Oct 29 |
| Severe (24°F) | Oct 5 | Oct 29 | Nov 20 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 27 | Sep 1 | Sep 3 | Sep 6 | Sep 10 | Sep 13 | Sep 16 | Sep 20 | Sep 25 |
| 32°F | Sep 6 | Sep 12 | Sep 16 | Sep 20 | Sep 23 | Sep 26 | Sep 29 | Oct 3 | Oct 9 |
| 28°F | Sep 20 | Sep 26 | Oct 1 | Oct 4 | Oct 8 | Oct 11 | Oct 16 | Oct 21 | Oct 29 |
| 24°F | Oct 5 | Oct 12 | Oct 18 | Oct 24 | Oct 29 | Nov 1 | Nov 6 | Nov 11 | Nov 20 |
| 20°F | Oct 23 | Nov 1 | Nov 5 | Nov 10 | Nov 15 | Nov 21 | Nov 24 | Nov 29 | Dec 5 |
| 16°F | Nov 5 | Nov 12 | Nov 19 | Nov 24 | Nov 28 | Dec 1 | Dec 4 | Dec 10 | Dec 16 |
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: Elk Rvr, Id, about 17.1 miles away@if(!empty($station['elevation_ft'])), at 2,866 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 Fernwood, ID?
On average, the last spring frost (32°F) around Fernwood, ID is about May 16. In cooler years it can run later, so for a safer bet many gardeners wait until May 2.
When is the first frost in the fall?
The first fall frost around Fernwood, ID typically arrives about Sep 23. 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 16 on average, or May 2 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 128 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 83812 Planting calendar → Idaho frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026