Last spring frost
Jun 5
Frost Dates for Spencer, ID
First fall frost
Sep 20
Growing season
106 days
Hardiness zone
5b
In an average year around Spencer, ID, the last spring frost (32°F) is about Jun 5 and the first fall frost is about Sep 20, giving roughly a 106-day growing season. To be safe most years, wait until May 11 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 2 | Jun 18 | Jun 5 |
| Freeze (32°F) | Jun 21 | Jun 5 | May 11 |
| Hard (28°F) | Jun 8 | May 10 | Apr 25 |
| Severe (24°F) | May 9 | Apr 24 | Apr 9 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jul 2 | Jun 28 | Jun 24 | Jun 21 | Jun 18 | Jun 15 | Jun 13 | Jun 9 | Jun 5 |
| 32°F | Jun 21 | Jun 16 | Jun 12 | Jun 8 | Jun 5 | May 31 | May 25 | May 19 | May 11 |
| 28°F | Jun 8 | May 30 | May 19 | May 14 | May 10 | May 7 | May 3 | May 1 | Apr 25 |
| 24°F | May 9 | May 3 | May 1 | Apr 28 | Apr 24 | Apr 22 | Apr 18 | Apr 14 | Apr 9 |
| 20°F | Apr 27 | Apr 21 | Apr 17 | Apr 14 | Apr 10 | Apr 7 | Apr 4 | Mar 31 | Mar 23 |
| 16°F | Apr 14 | Apr 8 | Apr 4 | Mar 31 | Mar 28 | Mar 22 | Mar 18 | Mar 13 | Mar 9 |
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 25 | Sep 8 | Sep 23 |
| Freeze (32°F) | Sep 3 | Sep 20 | Oct 4 |
| Hard (28°F) | Sep 14 | Oct 2 | Oct 15 |
| Severe (24°F) | Sep 28 | Oct 13 | Oct 27 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 25 | Aug 30 | Sep 2 | Sep 5 | Sep 8 | Sep 11 | Sep 14 | Sep 18 | Sep 23 |
| 32°F | Sep 3 | Sep 9 | Sep 12 | Sep 16 | Sep 20 | Sep 23 | Sep 26 | Sep 30 | Oct 4 |
| 28°F | Sep 14 | Sep 21 | Sep 26 | Sep 29 | Oct 2 | Oct 4 | Oct 7 | Oct 11 | Oct 15 |
| 24°F | Sep 28 | Oct 3 | Oct 6 | Oct 9 | Oct 13 | Oct 16 | Oct 19 | Oct 22 | Oct 27 |
| 20°F | Oct 9 | Oct 14 | Oct 17 | Oct 20 | Oct 23 | Oct 26 | Oct 29 | Nov 1 | Nov 5 |
| 16°F | Oct 19 | Oct 24 | Oct 27 | Oct 30 | Nov 1 | Nov 5 | Nov 8 | Nov 11 | Nov 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: Small 6N, Id, about 5.4 miles away@if(!empty($station['elevation_ft'])), at 5,740 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 Spencer, ID?
On average, the last spring frost (32°F) around Spencer, ID is about Jun 5. In cooler years it can run later, so for a safer bet many gardeners wait until May 11.
When is the first frost in the fall?
The first fall frost around Spencer, ID typically arrives about Sep 20. 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 5 on average, or May 11 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 106 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 83423 Planting calendar → Idaho frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026