Last spring frost
May 11
Frost Dates for Rockford Bay, ID
First fall frost
Oct 5
Growing season
143 days
Hardiness zone
6b
In an average year around Rockford Bay, ID, the last spring frost (32°F) is about May 11 and the first fall frost is about Oct 5, giving roughly a 143-day growing season. To be safe most years, wait until Apr 25 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 24 | Jun 7 | May 15 |
| Freeze (32°F) | Jun 4 | May 11 | Apr 25 |
| Hard (28°F) | May 10 | Apr 22 | Mar 29 |
| Severe (24°F) | Apr 19 | Mar 24 | Mar 5 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 24 | Jun 18 | Jun 14 | Jun 11 | Jun 7 | Jun 3 | May 30 | May 24 | May 15 |
| 32°F | Jun 4 | May 28 | May 21 | May 15 | May 11 | May 7 | May 3 | Apr 30 | Apr 25 |
| 28°F | May 10 | May 3 | Apr 29 | Apr 25 | Apr 22 | Apr 17 | Apr 12 | Apr 6 | Mar 29 |
| 24°F | Apr 19 | Apr 9 | Apr 2 | Mar 29 | Mar 24 | Mar 20 | Mar 15 | Mar 10 | Mar 5 |
| 20°F | Mar 25 | Mar 17 | Mar 13 | Mar 9 | Mar 6 | Mar 3 | Mar 1 | Feb 24 | Feb 15 |
| 16°F | Mar 15 | Mar 8 | Mar 3 | Feb 28 | Feb 25 | Feb 20 | Feb 14 | Feb 5 | Jan 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) | Aug 25 | Sep 20 | Oct 7 |
| Freeze (32°F) | Sep 15 | Oct 5 | Oct 21 |
| Hard (28°F) | Oct 2 | Oct 19 | Nov 6 |
| Severe (24°F) | Oct 15 | Nov 1 | Nov 23 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 25 | Sep 4 | Sep 10 | Sep 15 | Sep 20 | Sep 24 | Sep 29 | Oct 2 | Oct 7 |
| 32°F | Sep 15 | Sep 24 | Sep 29 | Oct 2 | Oct 5 | Oct 8 | Oct 12 | Oct 16 | Oct 21 |
| 28°F | Oct 2 | Oct 8 | Oct 12 | Oct 15 | Oct 19 | Oct 22 | Oct 25 | Oct 30 | Nov 6 |
| 24°F | Oct 15 | Oct 20 | Oct 25 | Oct 28 | Nov 1 | Nov 6 | Nov 11 | Nov 16 | Nov 23 |
| 20°F | Oct 25 | Nov 1 | Nov 8 | Nov 13 | Nov 19 | Nov 22 | Nov 27 | Nov 30 | Dec 6 |
| 16°F | Nov 5 | Nov 15 | Nov 23 | Nov 27 | Dec 1 | Dec 4 | Dec 8 | Dec 13 | Dec 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: Plummer 3 Wsw, Id, about 10 miles away@if(!empty($station['elevation_ft'])), at 2,905 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 Rockford Bay, ID?
On average, the last spring frost (32°F) around Rockford Bay, ID is about May 11. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 25.
When is the first frost in the fall?
The first fall frost around Rockford Bay, ID typically arrives about Oct 5. 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 11 on average, or Apr 25 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 143 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 83876 Planting calendar → Idaho frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026