Last spring frost
May 15
Frost Dates for Onaway, ID
First fall frost
Sep 21
Growing season
126 days
Hardiness zone
6b
In an average year around Onaway, ID, the last spring frost (32°F) is about May 15 and the first fall frost is about Sep 21, giving roughly a 126-day growing season. To be safe most years, wait until Apr 30 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 5 | Jun 10 | May 21 |
| Freeze (32°F) | Jun 2 | May 15 | Apr 30 |
| Hard (28°F) | May 13 | Apr 28 | Apr 4 |
| Severe (24°F) | Apr 27 | Mar 30 | Mar 7 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jul 5 | Jun 28 | Jun 20 | Jun 15 | Jun 10 | Jun 5 | Jun 1 | May 27 | May 21 |
| 32°F | Jun 2 | May 28 | May 23 | May 19 | May 15 | May 12 | May 8 | May 4 | Apr 30 |
| 28°F | May 13 | May 8 | May 3 | Apr 30 | Apr 28 | Apr 24 | Apr 19 | Apr 14 | Apr 4 |
| 24°F | Apr 27 | Apr 17 | Apr 9 | Apr 2 | Mar 30 | Mar 25 | Mar 19 | Mar 13 | Mar 7 |
| 20°F | Mar 30 | Mar 21 | Mar 15 | Mar 11 | Mar 7 | Mar 3 | Feb 28 | Feb 22 | Feb 14 |
| 16°F | Mar 12 | Mar 6 | Mar 2 | Feb 27 | Feb 23 | Feb 18 | Feb 12 | Feb 4 | Jan 24 |
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 15 | Sep 3 | Sep 21 |
| Freeze (32°F) | Aug 31 | Sep 21 | Oct 7 |
| Hard (28°F) | Sep 18 | Oct 5 | Oct 27 |
| Severe (24°F) | Oct 1 | Oct 20 | Nov 14 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 15 | Aug 23 | Aug 27 | Sep 1 | Sep 3 | Sep 6 | Sep 10 | Sep 15 | Sep 21 |
| 32°F | Aug 31 | Sep 6 | Sep 12 | Sep 17 | Sep 21 | Sep 24 | Sep 27 | Oct 1 | Oct 7 |
| 28°F | Sep 18 | Sep 26 | Sep 30 | Oct 2 | Oct 5 | Oct 8 | Oct 13 | Oct 18 | Oct 27 |
| 24°F | Oct 1 | Oct 6 | Oct 10 | Oct 16 | Oct 20 | Oct 26 | Oct 30 | Nov 5 | Nov 14 |
| 20°F | Oct 14 | Oct 21 | Oct 27 | Oct 31 | Nov 4 | Nov 10 | Nov 16 | Nov 23 | Nov 30 |
| 16°F | Oct 28 | Nov 4 | Nov 11 | Nov 17 | Nov 24 | Nov 28 | Dec 3 | Dec 10 | Dec 20 |
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: Potlatch 3 Nne, Id, about 2.9 miles away@if(!empty($station['elevation_ft'])), at 2,760 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 Onaway, ID?
On average, the last spring frost (32°F) around Onaway, ID is about May 15. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 30.
When is the first frost in the fall?
The first fall frost around Onaway, ID typically arrives about Sep 21. 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 15 on average, or Apr 30 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 126 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 83855 Planting calendar → Idaho frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026