Last spring frost
May 31
Frost Dates for Harrington, WA
First fall frost
Sep 12
Growing season
101 days
Hardiness zone
6b
In an average year around Harrington, WA, the last spring frost (32°F) is about May 31 and the first fall frost is about Sep 12, giving roughly a 101-day growing season. To be safe most years, wait until May 10 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%) |
|---|---|---|---|
| Freeze (32°F) | Jun 28 | May 31 | May 10 |
| Hard (28°F) | May 31 | May 9 | Apr 24 |
| Severe (24°F) | May 12 | Apr 26 | Mar 31 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 32°F | Jun 28 | Jun 18 | Jun 10 | Jun 4 | May 31 | May 26 | May 21 | May 16 | May 10 |
| 28°F | May 31 | May 21 | May 17 | May 12 | May 9 | May 5 | May 2 | Apr 29 | Apr 24 |
| 24°F | May 12 | May 6 | May 3 | Apr 29 | Apr 26 | Apr 22 | Apr 18 | Apr 12 | Mar 31 |
| 20°F | Apr 29 | Apr 21 | Apr 15 | Apr 7 | Mar 29 | Mar 21 | Mar 12 | Mar 5 | Feb 25 |
| 16°F | Mar 26 | Mar 12 | Mar 5 | Mar 1 | Feb 26 | Feb 22 | Feb 17 | Feb 10 | Feb 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%) |
|---|---|---|---|
| Freeze (32°F) | Aug 23 | Sep 12 | Oct 2 |
| Hard (28°F) | Sep 10 | Oct 1 | Oct 16 |
| Severe (24°F) | Sep 27 | Oct 11 | Oct 31 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 32°F | Aug 23 | Aug 30 | Sep 4 | Sep 8 | Sep 12 | Sep 17 | Sep 22 | Sep 27 | Oct 2 |
| 28°F | Sep 10 | Sep 16 | Sep 22 | Sep 27 | Oct 1 | Oct 3 | Oct 5 | Oct 10 | Oct 16 |
| 24°F | Sep 27 | Oct 1 | Oct 4 | Oct 7 | Oct 11 | Oct 15 | Oct 20 | Oct 24 | Oct 31 |
| 20°F | Oct 6 | Oct 14 | Oct 19 | Oct 22 | Oct 27 | Oct 31 | Nov 2 | Nov 8 | Nov 17 |
| 16°F | Oct 18 | Oct 24 | Oct 30 | Nov 3 | Nov 8 | Nov 13 | Nov 18 | Nov 24 | 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: Harrington, Wa, about 8 miles away@if(!empty($station['elevation_ft'])), at 2,159 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 Harrington, WA?
On average, the last spring frost (32°F) around Harrington, WA is about May 31. In cooler years it can run later, so for a safer bet many gardeners wait until May 10.
When is the first frost in the fall?
The first fall frost around Harrington, WA typically arrives about Sep 12. 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 31 on average, or May 10 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 101 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 99154 Planting calendar → Washington frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026