Last spring frost
May 31
Frost Dates for Smiths Ferry, ID
First fall frost
Sep 16
Growing season
108 days
Hardiness zone
7a
In an average year around Smiths Ferry, ID, the last spring frost (32°F) is about May 31 and the first fall frost is about Sep 16, giving roughly a 108-day growing season. To be safe most years, wait until May 8 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 4 | Jun 18 | Jun 1 |
| Freeze (32°F) | Jun 19 | May 31 | May 8 |
| Hard (28°F) | May 30 | May 7 | Apr 23 |
| Severe (24°F) | May 9 | Apr 22 | Apr 3 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jul 4 | Jun 29 | Jun 25 | Jun 21 | Jun 18 | Jun 15 | Jun 11 | Jun 7 | Jun 1 |
| 32°F | Jun 19 | Jun 13 | Jun 8 | Jun 3 | May 31 | May 25 | May 19 | May 15 | May 8 |
| 28°F | May 30 | May 21 | May 15 | May 11 | May 7 | May 3 | Apr 30 | Apr 27 | Apr 23 |
| 24°F | May 9 | May 3 | Apr 29 | Apr 26 | Apr 22 | Apr 18 | Apr 15 | Apr 10 | Apr 3 |
| 20°F | Apr 23 | Apr 15 | Apr 9 | Apr 4 | Mar 31 | Mar 26 | Mar 19 | Mar 12 | Mar 6 |
| 16°F | Mar 31 | Mar 21 | Mar 13 | Mar 9 | Mar 7 | Mar 3 | Feb 28 | Feb 25 | Feb 19 |
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 19 | Sep 4 | Sep 18 |
| Freeze (32°F) | Sep 2 | Sep 16 | Sep 30 |
| Hard (28°F) | Sep 14 | Sep 29 | Oct 13 |
| Severe (24°F) | Sep 26 | Oct 12 | Oct 26 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 19 | Aug 26 | Aug 30 | Sep 2 | Sep 4 | Sep 7 | Sep 10 | Sep 13 | Sep 18 |
| 32°F | Sep 2 | Sep 6 | Sep 10 | Sep 13 | Sep 16 | Sep 19 | Sep 22 | Sep 26 | Sep 30 |
| 28°F | Sep 14 | Sep 19 | Sep 23 | Sep 26 | Sep 29 | Oct 2 | Oct 4 | Oct 8 | Oct 13 |
| 24°F | Sep 26 | Oct 1 | Oct 5 | Oct 8 | Oct 12 | Oct 15 | Oct 18 | Oct 21 | Oct 26 |
| 20°F | Oct 8 | Oct 13 | Oct 17 | Oct 20 | Oct 24 | Oct 27 | Oct 31 | Nov 3 | Nov 11 |
| 16°F | Oct 19 | Oct 25 | Oct 30 | Nov 1 | Nov 5 | Nov 10 | Nov 14 | Nov 19 | Nov 26 |
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: Ola, Id, about 4.3 miles away@if(!empty($station['elevation_ft'])), at 3,075 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 Smiths Ferry, ID?
On average, the last spring frost (32°F) around Smiths Ferry, ID is about May 31. In cooler years it can run later, so for a safer bet many gardeners wait until May 8.
When is the first frost in the fall?
The first fall frost around Smiths Ferry, ID typically arrives about Sep 16. 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 31 on average, or May 8 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 108 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 83657 Planting calendar → Idaho frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026