Last spring frost
May 6
Frost Dates for Unalaska, AK
First fall frost
Oct 18
Growing season
164 days
In an average year around Unalaska, AK, the last spring frost (32°F) is about May 6 and the first fall frost is about Oct 18, giving roughly a 164-day growing season. To be safe most years, wait until Apr 23 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 11 | May 26 | May 10 |
| Freeze (32°F) | May 22 | May 6 | Apr 23 |
| Hard (28°F) | May 5 | Apr 19 | Apr 3 |
| Severe (24°F) | Apr 17 | Mar 31 | Mar 1 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Jun 11 | Jun 4 | Jun 1 | May 29 | May 26 | May 23 | May 19 | May 15 | May 10 |
| 32°F | May 22 | May 16 | May 12 | May 9 | May 6 | May 4 | May 1 | Apr 28 | Apr 23 |
| 28°F | May 5 | May 1 | Apr 26 | Apr 23 | Apr 19 | Apr 15 | Apr 12 | Apr 9 | Apr 3 |
| 24°F | Apr 17 | Apr 11 | Apr 7 | Apr 3 | Mar 31 | Mar 28 | Mar 22 | Mar 13 | Mar 1 |
| 20°F | Apr 3 | Mar 30 | Mar 24 | Mar 17 | Mar 8 | Mar 1 | Feb 20 | Feb 9 | Jan 26 |
| 16°F | Mar 29 | Mar 18 | Mar 7 | Feb 28 | Feb 19 | Feb 9 | Feb 1 | Jan 24 | Jan 1 |
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 | Oct 1 | Oct 19 |
| Freeze (32°F) | Sep 20 | Oct 18 | Nov 5 |
| Hard (28°F) | Oct 10 | Nov 4 | Dec 1 |
| Severe (24°F) | Oct 23 | Nov 22 | Jan 4 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 4 | Sep 14 | Sep 20 | Sep 26 | Oct 1 | Oct 4 | Oct 8 | Oct 13 | Oct 19 |
| 32°F | Sep 20 | Oct 2 | Oct 8 | Oct 14 | Oct 18 | Oct 23 | Oct 27 | Nov 1 | Nov 5 |
| 28°F | Oct 10 | Oct 19 | Oct 26 | Nov 1 | Nov 4 | Nov 8 | Nov 13 | Nov 19 | Dec 1 |
| 24°F | Oct 23 | Nov 1 | Nov 6 | Nov 13 | Nov 22 | Dec 2 | Dec 11 | Dec 24 | Jan 4 |
| 20°F | Nov 1 | Nov 10 | Nov 22 | Dec 12 | Dec 28 | Jan 5 | Jan 14 | Jan 25 | Feb 12 |
| 16°F | Nov 10 | Nov 30 | Jan 2 | Jan 12 | Jan 21 | Jan 29 | Feb 5 | Feb 18 | Mar 7 |
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: Dutch Harbor, Ak, about 2.9 miles away@if(!empty($station['elevation_ft'])), at 10 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 Unalaska, AK?
On average, the last spring frost (32°F) around Unalaska, AK is about May 6. In cooler years it can run later, so for a safer bet many gardeners wait until Apr 23.
When is the first frost in the fall?
The first fall frost around Unalaska, AK typically arrives about Oct 18. 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 6 on average, or Apr 23 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 164 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 99685 Planting calendar → Alaska frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026