Last spring frost
May 2
Frost Dates for Mountain Home AFB, ID
First fall frost
Oct 8
Growing season
157 days
Hardiness zone
7a
In an average year around Mountain Home AFB, ID, the last spring frost (32°F) is about May 2 and the first fall frost is about Oct 8, giving roughly a 157-day growing season. To be safe most years, wait until Apr 18 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 10 | May 17 | Apr 30 |
| Freeze (32°F) | May 23 | May 2 | Apr 18 |
| Hard (28°F) | May 8 | Apr 18 | Apr 1 |
| Severe (24°F) | Apr 26 | Apr 2 | Mar 7 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 10 | Jun 3 | May 28 | May 22 | May 17 | May 14 | May 10 | May 6 | Apr 30 |
| 32°F | May 23 | May 15 | May 10 | May 6 | May 2 | Apr 30 | Apr 26 | Apr 23 | Apr 18 |
| 28°F | May 8 | May 1 | Apr 26 | Apr 22 | Apr 18 | Apr 15 | Apr 12 | Apr 7 | Apr 1 |
| 24°F | Apr 26 | Apr 17 | Apr 9 | Apr 5 | Apr 2 | Mar 28 | Mar 22 | Mar 16 | Mar 7 |
| 20°F | Apr 3 | Mar 27 | Mar 18 | Mar 13 | Mar 9 | Mar 4 | Feb 28 | Feb 23 | Feb 14 |
| 16°F | Mar 10 | Mar 3 | Feb 27 | Feb 23 | Feb 19 | Feb 14 | Feb 9 | Feb 2 | Jan 18 |
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) | Sep 11 | Sep 28 | Oct 11 |
| Freeze (32°F) | Sep 25 | Oct 8 | Oct 24 |
| Hard (28°F) | Oct 4 | Oct 20 | Nov 5 |
| Severe (24°F) | Oct 14 | Oct 31 | Nov 21 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 11 | Sep 18 | Sep 22 | Sep 25 | Sep 28 | Sep 30 | Oct 3 | Oct 6 | Oct 11 |
| 32°F | Sep 25 | Sep 29 | Oct 1 | Oct 5 | Oct 8 | Oct 11 | Oct 14 | Oct 18 | Oct 24 |
| 28°F | Oct 4 | Oct 9 | Oct 14 | Oct 17 | Oct 20 | Oct 23 | Oct 26 | Nov 1 | Nov 5 |
| 24°F | Oct 14 | Oct 19 | Oct 23 | Oct 27 | Oct 31 | Nov 3 | Nov 7 | Nov 13 | Nov 21 |
| 20°F | Oct 21 | Oct 28 | Nov 1 | Nov 6 | Nov 11 | Nov 16 | Nov 21 | Nov 26 | Dec 1 |
| 16°F | Oct 31 | Nov 7 | Nov 13 | Nov 18 | Nov 25 | Nov 29 | Dec 3 | Dec 9 | Dec 17 |
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: Mtn Home, Id, about 9.4 miles away@if(!empty($station['elevation_ft'])), at 3,140 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 Mountain Home AFB, ID?
On average, the last spring frost (32°F) around Mountain Home AFB, ID is about May 2. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 18.
When is the first frost in the fall?
The first fall frost around Mountain Home AFB, ID typically arrives about Oct 8. 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 2 on average, or Apr 18 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 157 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 83648 Planting calendar → Idaho frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026