Last spring frost
May 24
Frost Dates for Arco, ID
First fall frost
Oct 1
Growing season
130 days
Hardiness zone
5a
In an average year around Arco, ID, the last spring frost (32°F) is about May 24 and the first fall frost is about Oct 1, giving roughly a 130-day growing season. To be safe most years, wait until May 4 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 23 | Jun 9 | May 21 |
| Freeze (32°F) | Jun 15 | May 24 | May 4 |
| Hard (28°F) | May 27 | May 3 | Apr 18 |
| Severe (24°F) | May 5 | Apr 18 | Apr 3 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 23 | Jun 18 | Jun 15 | Jun 12 | Jun 9 | Jun 5 | Jun 2 | May 29 | May 21 |
| 32°F | Jun 15 | Jun 8 | Jun 2 | May 30 | May 24 | May 19 | May 15 | May 9 | May 4 |
| 28°F | May 27 | May 16 | May 10 | May 6 | May 3 | Apr 30 | Apr 27 | Apr 23 | Apr 18 |
| 24°F | May 5 | Apr 30 | Apr 25 | Apr 21 | Apr 18 | Apr 15 | Apr 12 | Apr 8 | Apr 3 |
| 20°F | Apr 21 | Apr 13 | Apr 9 | Apr 6 | Apr 3 | Mar 31 | Mar 29 | Mar 23 | Mar 15 |
| 16°F | Apr 6 | Apr 1 | Mar 29 | Mar 23 | Mar 19 | Mar 15 | Mar 11 | Mar 7 | Mar 2 |
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 4 | Sep 19 | Oct 3 |
| Freeze (32°F) | Sep 16 | Oct 1 | Oct 14 |
| Hard (28°F) | Sep 28 | Oct 13 | Oct 26 |
| Severe (24°F) | Oct 9 | Oct 24 | Nov 7 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 4 | Sep 9 | Sep 14 | Sep 17 | Sep 19 | Sep 23 | Sep 25 | Sep 28 | Oct 3 |
| 32°F | Sep 16 | Sep 21 | Sep 25 | Sep 28 | Oct 1 | Oct 4 | Oct 7 | Oct 10 | Oct 14 |
| 28°F | Sep 28 | Oct 2 | Oct 6 | Oct 10 | Oct 13 | Oct 16 | Oct 19 | Oct 22 | Oct 26 |
| 24°F | Oct 9 | Oct 15 | Oct 19 | Oct 22 | Oct 24 | Oct 27 | Oct 30 | Nov 2 | Nov 7 |
| 20°F | Oct 19 | Oct 24 | Oct 27 | Oct 30 | Nov 1 | Nov 5 | Nov 8 | Nov 11 | Nov 16 |
| 16°F | Oct 25 | Oct 31 | Nov 4 | Nov 7 | Nov 11 | Nov 14 | Nov 17 | Nov 21 | Nov 25 |
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: Arco 17 Sw, Id, about 9.7 miles away@if(!empty($station['elevation_ft'])), at 5,920 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 Arco, ID?
On average, the last spring frost (32°F) around Arco, ID is about May 24. In cooler years it can run later, so for a safer bet many gardeners wait until May 4.
When is the first frost in the fall?
The first fall frost around Arco, ID typically arrives about Oct 1. 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 24 on average, or May 4 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 130 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 83213 Planting calendar → Idaho frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026