Last spring frost
May 30
Frost Dates for Donnelly, ID
First fall frost
Sep 19
Growing season
110 days
Hardiness zone
5a
In an average year around Donnelly, ID, the last spring frost (32°F) is about May 30 and the first fall frost is about Sep 19, giving roughly a 110-day growing season. To be safe most years, wait until May 10 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 21 | May 30 | May 10 |
| Hard (28°F) | May 28 | May 6 | Apr 21 |
| Severe (24°F) | May 6 | Apr 19 | Apr 4 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 32°F | Jun 21 | Jun 14 | Jun 8 | Jun 3 | May 30 | May 24 | May 19 | May 15 | May 10 |
| 28°F | May 28 | May 18 | May 13 | May 10 | May 6 | May 3 | May 1 | Apr 27 | Apr 21 |
| 24°F | May 6 | Apr 30 | Apr 27 | Apr 23 | Apr 19 | Apr 16 | Apr 12 | Apr 9 | Apr 4 |
| 20°F | Apr 21 | Apr 14 | Apr 10 | Apr 7 | Apr 4 | Apr 1 | Mar 29 | Mar 23 | Mar 18 |
| 16°F | Apr 10 | Apr 4 | Mar 31 | Mar 27 | Mar 23 | Mar 19 | Mar 15 | Mar 11 | Mar 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%) |
|---|---|---|---|
| Freeze (32°F) | Sep 3 | Sep 19 | Oct 4 |
| Hard (28°F) | Sep 15 | Oct 2 | Oct 18 |
| Severe (24°F) | Sep 30 | Oct 16 | Nov 3 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 32°F | Sep 3 | Sep 7 | Sep 12 | Sep 15 | Sep 19 | Sep 24 | Sep 27 | Oct 1 | Oct 4 |
| 28°F | Sep 15 | Sep 22 | Sep 27 | Sep 30 | Oct 2 | Oct 5 | Oct 9 | Oct 13 | Oct 18 |
| 24°F | Sep 30 | Oct 4 | Oct 8 | Oct 12 | Oct 16 | Oct 20 | Oct 23 | Oct 28 | Nov 3 |
| 20°F | Oct 13 | Oct 19 | Oct 23 | Oct 26 | Oct 30 | Nov 2 | Nov 6 | Nov 11 | Nov 18 |
| 16°F | Oct 25 | Oct 30 | Nov 3 | Nov 8 | Nov 12 | Nov 16 | Nov 20 | Nov 23 | Nov 28 |
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: Cascade 1 Nw, Id, about 12.6 miles away@if(!empty($station['elevation_ft'])), at 4,896 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 Donnelly, ID?
On average, the last spring frost (32°F) around Donnelly, ID is about May 30. In cooler years it can run later, so for a safer bet many gardeners wait until May 10.
When is the first frost in the fall?
The first fall frost around Donnelly, ID typically arrives about Sep 19. 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 30 on average, or May 10 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 110 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 83615 Planting calendar → Idaho frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026