Last spring frost
Jun 1
Frost Dates for Sula, ID
First fall frost
Sep 17
Growing season
107 days
Hardiness zone
5b
In an average year around Sula, ID, the last spring frost (32°F) is about Jun 1 and the first fall frost is about Sep 17, giving roughly a 107-day growing season. To be safe most years, wait until May 14 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 10 | Jun 20 | Jun 5 |
| Freeze (32°F) | Jun 19 | Jun 1 | May 14 |
| Hard (28°F) | May 27 | May 10 | Apr 28 |
| Severe (24°F) | May 9 | Apr 25 | Apr 9 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jul 10 | Jul 2 | Jun 28 | Jun 24 | Jun 20 | Jun 18 | Jun 15 | Jun 11 | Jun 5 |
| 32°F | Jun 19 | Jun 13 | Jun 9 | Jun 5 | Jun 1 | May 29 | May 24 | May 20 | May 14 |
| 28°F | May 27 | May 20 | May 17 | May 13 | May 10 | May 8 | May 5 | May 2 | Apr 28 |
| 24°F | May 9 | May 4 | May 1 | Apr 29 | Apr 25 | Apr 22 | Apr 18 | Apr 13 | Apr 9 |
| 20°F | Apr 25 | Apr 19 | Apr 14 | Apr 11 | Apr 7 | Apr 4 | Apr 2 | Mar 30 | Mar 22 |
| 16°F | Apr 8 | Apr 3 | Mar 31 | Mar 27 | Mar 23 | Mar 19 | Mar 15 | Mar 12 | Mar 6 |
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 24 | Sep 3 | Sep 17 |
| Freeze (32°F) | Sep 2 | Sep 17 | Oct 1 |
| Hard (28°F) | Sep 14 | Sep 30 | Oct 15 |
| Severe (24°F) | Sep 28 | Oct 14 | Oct 30 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 24 | Aug 28 | Aug 31 | Sep 1 | Sep 3 | Sep 6 | Sep 9 | Sep 13 | Sep 17 |
| 32°F | Sep 2 | Sep 7 | Sep 11 | Sep 13 | Sep 17 | Sep 20 | Sep 23 | Sep 26 | Oct 1 |
| 28°F | Sep 14 | Sep 20 | Sep 24 | Sep 27 | Sep 30 | Oct 2 | Oct 5 | Oct 9 | Oct 15 |
| 24°F | Sep 28 | Oct 3 | Oct 5 | Oct 10 | Oct 14 | Oct 17 | Oct 20 | Oct 23 | Oct 30 |
| 20°F | Oct 7 | Oct 15 | Oct 20 | Oct 22 | Oct 26 | Oct 29 | Oct 31 | Nov 5 | Nov 9 |
| 16°F | Oct 20 | Oct 25 | Oct 29 | Nov 1 | Nov 5 | Nov 8 | Nov 11 | Nov 15 | Nov 19 |
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: Gibbonsville #2, Id, about 2.9 miles away@if(!empty($station['elevation_ft'])), at 4,480 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 Sula, ID?
On average, the last spring frost (32°F) around Sula, ID is about Jun 1. In cooler years it can run later, so for a safer bet many gardeners wait until May 14.
When is the first frost in the fall?
The first fall frost around Sula, ID typically arrives about Sep 17. 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 Jun 1 on average, or May 14 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 107 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 83463 Planting calendar → Idaho frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026