Last spring frost
Mar 27
Frost Dates for Hamilton, WA
First fall frost
Nov 6
Growing season
224 days
Hardiness zone
8b
In an average year around Hamilton, WA, the last spring frost (32°F) is about Mar 27 and the first fall frost is about Nov 6, giving roughly a 224-day growing season. To be safe most years, wait until Mar 8 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 11 | Apr 22 | Apr 1 |
| Freeze (32°F) | Apr 17 | Mar 27 | Mar 8 |
| Hard (28°F) | Mar 22 | Mar 1 | Feb 2 |
| Severe (24°F) | Mar 2 | Feb 4 | Dec 25 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 11 | May 5 | May 1 | Apr 26 | Apr 22 | Apr 18 | Apr 13 | Apr 8 | Apr 1 |
| 32°F | Apr 17 | Apr 7 | Apr 3 | Mar 31 | Mar 27 | Mar 23 | Mar 19 | Mar 13 | Mar 8 |
| 28°F | Mar 22 | Mar 14 | Mar 9 | Mar 5 | Mar 1 | Feb 26 | Feb 22 | Feb 16 | Feb 2 |
| 24°F | Mar 2 | Feb 26 | Feb 20 | Feb 13 | Feb 4 | Jan 30 | Jan 19 | Jan 9 | Dec 25 |
| 20°F | Feb 20 | Feb 6 | Jan 31 | Jan 22 | Jan 13 | Jan 6 | Dec 31 | Dec 21 | Dec 10 |
| 16°F | Feb 1 | Jan 20 | Jan 11 | Jan 3 | Dec 31 | Dec 24 | Dec 18 | Dec 10 | Dec 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) | Oct 1 | Oct 17 | Nov 8 |
| Freeze (32°F) | Oct 15 | Nov 6 | Nov 28 |
| Hard (28°F) | Nov 1 | Nov 24 | Dec 19 |
| Severe (24°F) | Nov 18 | Dec 11 | Jan 14 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 1 | Oct 5 | Oct 9 | Oct 13 | Oct 17 | Oct 22 | Oct 26 | Nov 1 | Nov 8 |
| 32°F | Oct 15 | Oct 23 | Oct 28 | Nov 1 | Nov 6 | Nov 11 | Nov 16 | Nov 21 | Nov 28 |
| 28°F | Nov 1 | Nov 9 | Nov 15 | Nov 19 | Nov 24 | Nov 28 | Dec 2 | Dec 10 | Dec 19 |
| 24°F | Nov 18 | Nov 25 | Nov 30 | Dec 5 | Dec 11 | Dec 17 | Dec 23 | Dec 31 | Jan 14 |
| 20°F | Nov 26 | Dec 2 | Dec 11 | Dec 18 | Dec 24 | Dec 30 | Jan 4 | Jan 15 | Feb 1 |
| 16°F | Nov 28 | Dec 6 | Dec 13 | Dec 19 | Dec 24 | Dec 30 | Jan 2 | Jan 13 | Jan 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: Sedro-Woolley, Wa, about 11.3 miles away@if(!empty($station['elevation_ft'])), at 60 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 Hamilton, WA?
On average, the last spring frost (32°F) around Hamilton, WA is about Mar 27. In cooler years it can run later, so for a safer bet many gardeners wait until Mar 8.
When is the first frost in the fall?
The first fall frost around Hamilton, WA typically arrives about Nov 6. 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 Mar 27 on average, or Mar 8 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 224 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 98255 Planting calendar → Washington frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026