Last spring frost
May 23
Frost Dates for Arimo, ID
First fall frost
Sep 24
Growing season
121 days
Hardiness zone
6b
In an average year around Arimo, ID, the last spring frost (32°F) is about May 23 and the first fall frost is about Sep 24, giving roughly a 121-day growing season. To be safe most years, wait until May 6 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) | Jun 28 | Jun 11 | May 24 |
| Freeze (32°F) | Jun 10 | May 23 | May 6 |
| Hard (28°F) | May 21 | May 4 | Apr 20 |
| Severe (24°F) | May 3 | Apr 19 | Apr 2 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 28 | Jun 21 | Jun 17 | Jun 14 | Jun 11 | Jun 7 | Jun 4 | May 31 | May 24 |
| 32°F | Jun 10 | Jun 5 | May 31 | May 27 | May 23 | May 19 | May 15 | May 11 | May 6 |
| 28°F | May 21 | May 14 | May 10 | May 7 | May 4 | May 2 | Apr 29 | Apr 26 | Apr 20 |
| 24°F | May 3 | Apr 29 | Apr 26 | Apr 23 | Apr 19 | Apr 17 | Apr 13 | Apr 8 | Apr 2 |
| 20°F | Apr 18 | Apr 12 | Apr 7 | Apr 4 | Apr 1 | Mar 29 | Mar 25 | Mar 17 | Mar 12 |
| 16°F | Apr 3 | Mar 28 | Mar 21 | Mar 16 | Mar 12 | Mar 8 | Mar 5 | Mar 2 | Feb 26 |
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 28 | Sep 11 | Sep 25 |
| Freeze (32°F) | Sep 7 | Sep 24 | Oct 7 |
| Hard (28°F) | Sep 20 | Oct 4 | Oct 19 |
| Severe (24°F) | Oct 2 | Oct 17 | Nov 1 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 28 | Sep 1 | Sep 4 | Sep 7 | Sep 11 | Sep 14 | Sep 17 | Sep 20 | Sep 25 |
| 32°F | Sep 7 | Sep 13 | Sep 18 | Sep 21 | Sep 24 | Sep 26 | Sep 29 | Oct 2 | Oct 7 |
| 28°F | Sep 20 | Sep 26 | Sep 30 | Oct 2 | Oct 4 | Oct 7 | Oct 11 | Oct 15 | Oct 19 |
| 24°F | Oct 2 | Oct 6 | Oct 11 | Oct 14 | Oct 17 | Oct 19 | Oct 23 | Oct 27 | Nov 1 |
| 20°F | Oct 14 | Oct 18 | Oct 22 | Oct 25 | Oct 28 | Oct 31 | Nov 3 | Nov 8 | Nov 14 |
| 16°F | Oct 23 | Oct 28 | Nov 1 | Nov 4 | Nov 7 | Nov 11 | Nov 16 | Nov 21 | Nov 25 |
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: Mccammon, Id, about 9.7 miles away@if(!empty($station['elevation_ft'])), at 4,770 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 Arimo, ID?
On average, the last spring frost (32°F) around Arimo, ID is about May 23. In cooler years it can run later, so for a safer bet many gardeners wait until May 6.
When is the first frost in the fall?
The first fall frost around Arimo, ID typically arrives about Sep 24. 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 23 on average, or May 6 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 121 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 83214 Planting calendar → Idaho frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026