Last spring frost
Apr 22
Frost Dates for New Plymouth, ID
First fall frost
Oct 9
Growing season
168 days
Hardiness zone
7a
In an average year around New Plymouth, ID, the last spring frost (32°F) is about Apr 22 and the first fall frost is about Oct 9, giving roughly a 168-day growing season. To be safe most years, wait until Apr 7 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) | May 21 | May 5 | Apr 21 |
| Freeze (32°F) | May 7 | Apr 22 | Apr 7 |
| Hard (28°F) | Apr 23 | Apr 6 | Mar 18 |
| Severe (24°F) | Apr 6 | Mar 16 | Feb 27 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 21 | May 15 | May 11 | May 8 | May 5 | May 2 | Apr 29 | Apr 26 | Apr 21 |
| 32°F | May 7 | May 2 | Apr 29 | Apr 26 | Apr 22 | Apr 20 | Apr 17 | Apr 13 | Apr 7 |
| 28°F | Apr 23 | Apr 19 | Apr 14 | Apr 9 | Apr 6 | Apr 2 | Mar 30 | Mar 25 | Mar 18 |
| 24°F | Apr 6 | Apr 1 | Mar 27 | Mar 20 | Mar 16 | Mar 11 | Mar 7 | Mar 3 | Feb 27 |
| 20°F | Mar 16 | Mar 7 | Mar 3 | Mar 1 | Feb 26 | Feb 22 | Feb 18 | Feb 13 | Feb 6 |
| 16°F | Feb 28 | Feb 24 | Feb 19 | Feb 15 | Feb 10 | Feb 6 | Feb 1 | Jan 25 | Jan 12 |
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 16 | Sep 30 | Oct 12 |
| Freeze (32°F) | Sep 26 | Oct 9 | Oct 23 |
| Hard (28°F) | Oct 6 | Oct 21 | Nov 4 |
| Severe (24°F) | Oct 19 | Nov 1 | Nov 20 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 16 | Sep 20 | Sep 24 | Sep 27 | Sep 30 | Oct 2 | Oct 5 | Oct 8 | Oct 12 |
| 32°F | Sep 26 | Oct 1 | Oct 4 | Oct 7 | Oct 9 | Oct 12 | Oct 15 | Oct 18 | Oct 23 |
| 28°F | Oct 6 | Oct 11 | Oct 15 | Oct 18 | Oct 21 | Oct 24 | Oct 27 | Oct 31 | Nov 4 |
| 24°F | Oct 19 | Oct 23 | Oct 27 | Oct 30 | Nov 1 | Nov 5 | Nov 9 | Nov 14 | Nov 20 |
| 20°F | Oct 27 | Nov 1 | Nov 6 | Nov 11 | Nov 14 | Nov 19 | Nov 22 | Nov 28 | Dec 5 |
| 16°F | Nov 4 | Nov 12 | Nov 18 | Nov 22 | Nov 26 | Nov 30 | Dec 5 | Dec 11 | Dec 21 |
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: Ontario Ksrv, Or, about 11.1 miles away@if(!empty($station['elevation_ft'])), at 2,145 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 New Plymouth, ID?
On average, the last spring frost (32°F) around New Plymouth, ID is about Apr 22. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 7.
When is the first frost in the fall?
The first fall frost around New Plymouth, ID typically arrives about Oct 9. 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 Apr 22 on average, or Apr 7 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 168 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 83655 Planting calendar → Idaho frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026