Last spring frost
May 15
Frost Dates for Cambridge, ID
First fall frost
Sep 27
Growing season
134 days
Hardiness zone
6a
In an average year around Cambridge, ID, the last spring frost (32°F) is about May 15 and the first fall frost is about Sep 27, giving roughly a 134-day growing season. To be safe most years, wait until Apr 29 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 21 | Jun 3 | May 15 |
| Freeze (32°F) | Jun 4 | May 15 | Apr 29 |
| Hard (28°F) | May 15 | Apr 28 | Apr 8 |
| Severe (24°F) | Apr 29 | Apr 6 | Mar 16 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 21 | Jun 15 | Jun 10 | Jun 7 | Jun 3 | May 30 | May 26 | May 20 | May 15 |
| 32°F | Jun 4 | May 29 | May 22 | May 17 | May 15 | May 11 | May 8 | May 3 | Apr 29 |
| 28°F | May 15 | May 8 | May 3 | May 1 | Apr 28 | Apr 24 | Apr 20 | Apr 15 | Apr 8 |
| 24°F | Apr 29 | Apr 21 | Apr 15 | Apr 10 | Apr 6 | Apr 2 | Mar 29 | Mar 23 | Mar 16 |
| 20°F | Apr 6 | Mar 31 | Mar 27 | Mar 21 | Mar 17 | Mar 13 | Mar 10 | Mar 6 | Mar 1 |
| 16°F | Mar 21 | Mar 15 | Mar 10 | Mar 7 | Mar 4 | Mar 2 | Feb 27 | Feb 23 | Feb 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 2 | Sep 16 | Sep 30 |
| Freeze (32°F) | Sep 12 | Sep 27 | Oct 9 |
| Hard (28°F) | Sep 23 | Oct 7 | Oct 22 |
| Severe (24°F) | Oct 5 | Oct 20 | Nov 4 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 2 | Sep 6 | Sep 10 | Sep 13 | Sep 16 | Sep 19 | Sep 22 | Sep 25 | Sep 30 |
| 32°F | Sep 12 | Sep 17 | Sep 21 | Sep 24 | Sep 27 | Sep 30 | Oct 2 | Oct 5 | Oct 9 |
| 28°F | Sep 23 | Sep 28 | Oct 2 | Oct 4 | Oct 7 | Oct 9 | Oct 13 | Oct 17 | Oct 22 |
| 24°F | Oct 5 | Oct 9 | Oct 14 | Oct 17 | Oct 20 | Oct 23 | Oct 26 | Oct 31 | Nov 4 |
| 20°F | Oct 17 | Oct 23 | Oct 26 | Oct 31 | Nov 1 | Nov 3 | Nov 8 | Nov 13 | Nov 20 |
| 16°F | Oct 28 | Nov 2 | Nov 5 | Nov 9 | Nov 13 | Nov 17 | Nov 22 | Nov 26 | Dec 2 |
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: Cambridge, Id, about 13.5 miles away@if(!empty($station['elevation_ft'])), at 2,650 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 Cambridge, ID?
On average, the last spring frost (32°F) around Cambridge, ID is about May 15. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 29.
When is the first frost in the fall?
The first fall frost around Cambridge, ID typically arrives about Sep 27. 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 15 on average, or Apr 29 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 134 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 83632 Planting calendar → Idaho frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026