Last spring frost
Apr 24
Frost Dates for Boise City, ID
First fall frost
Oct 21
Growing season
179 days
Hardiness zone
7a
In an average year around Boise City, ID, the last spring frost (32°F) is about Apr 24 and the first fall frost is about Oct 21, giving roughly a 179-day growing season. To be safe most years, wait until Apr 4 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) | May 29 | May 8 | Apr 23 |
| Freeze (32°F) | May 9 | Apr 24 | Apr 4 |
| Hard (28°F) | Apr 25 | Apr 2 | Mar 10 |
| Severe (24°F) | Apr 4 | Mar 9 | Feb 16 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 29 | May 19 | May 14 | May 10 | May 8 | May 4 | May 1 | Apr 28 | Apr 23 |
| 32°F | May 9 | May 4 | Apr 30 | Apr 27 | Apr 24 | Apr 21 | Apr 17 | Apr 12 | Apr 4 |
| 28°F | Apr 25 | Apr 18 | Apr 12 | Apr 6 | Apr 2 | Mar 30 | Mar 24 | Mar 18 | Mar 10 |
| 24°F | Apr 4 | Mar 27 | Mar 19 | Mar 13 | Mar 9 | Mar 4 | Mar 1 | Feb 24 | Feb 16 |
| 20°F | Mar 9 | Mar 2 | Feb 27 | Feb 23 | Feb 19 | Feb 14 | Feb 9 | Feb 2 | Jan 20 |
| 16°F | Feb 25 | Feb 18 | Feb 13 | Feb 7 | Feb 2 | Jan 25 | Jan 15 | Jan 5 | Dec 25 |
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 25 | Oct 8 | Oct 25 |
| Freeze (32°F) | Oct 5 | Oct 21 | Nov 5 |
| Hard (28°F) | Oct 17 | Oct 31 | Nov 19 |
| Severe (24°F) | Oct 24 | Nov 13 | Dec 1 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 25 | Sep 30 | Oct 3 | Oct 6 | Oct 8 | Oct 11 | Oct 14 | Oct 19 | Oct 25 |
| 32°F | Oct 5 | Oct 10 | Oct 14 | Oct 18 | Oct 21 | Oct 24 | Oct 27 | Oct 31 | Nov 5 |
| 28°F | Oct 17 | Oct 21 | Oct 25 | Oct 29 | Oct 31 | Nov 4 | Nov 8 | Nov 13 | Nov 19 |
| 24°F | Oct 24 | Oct 30 | Nov 4 | Nov 9 | Nov 13 | Nov 17 | Nov 21 | Nov 25 | Dec 1 |
| 20°F | Nov 5 | Nov 12 | Nov 17 | Nov 21 | Nov 25 | Nov 29 | Dec 3 | Dec 8 | Dec 15 |
| 16°F | Nov 14 | Nov 23 | Nov 27 | Dec 2 | Dec 7 | Dec 11 | Dec 16 | Dec 24 | Jan 4 |
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: Boise Air Terminal, Id, about 1.3 miles away@if(!empty($station['elevation_ft'])), at 2,814 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 Boise City, ID?
On average, the last spring frost (32°F) around Boise City, ID is about Apr 24. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 4.
When is the first frost in the fall?
The first fall frost around Boise City, ID typically arrives about Oct 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 Apr 24 on average, or Apr 4 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 179 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 83705 Planting calendar → Idaho frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026