Last spring frost
Apr 8
Frost Dates for Castle Rock, WA
First fall frost
Nov 5
Growing season
210 days
Hardiness zone
8b
In an average year around Castle Rock, WA, the last spring frost (32°F) is about Apr 8 and the first fall frost is about Nov 5, giving roughly a 210-day growing season. To be safe most years, wait until Mar 11 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 24 | May 3 | Apr 15 |
| Freeze (32°F) | May 2 | Apr 8 | Mar 11 |
| Hard (28°F) | Apr 4 | Mar 6 | Feb 6 |
| Severe (24°F) | Mar 3 | Feb 10 | Dec 14 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 24 | May 16 | May 10 | May 7 | May 3 | Apr 30 | Apr 27 | Apr 22 | Apr 15 |
| 32°F | May 2 | Apr 26 | Apr 20 | Apr 14 | Apr 8 | Apr 2 | Mar 29 | Mar 21 | Mar 11 |
| 28°F | Apr 4 | Mar 27 | Mar 17 | Mar 11 | Mar 6 | Feb 28 | Feb 24 | Feb 17 | Feb 6 |
| 24°F | Mar 3 | Feb 27 | Feb 21 | Feb 15 | Feb 10 | Jan 30 | Jan 14 | Jan 1 | Dec 14 |
| 20°F | Feb 22 | Feb 14 | Feb 4 | Jan 22 | Jan 6 | Dec 30 | Dec 19 | Dec 10 | Dec 2 |
| 16°F | Feb 12 | Jan 31 | Jan 8 | Dec 30 | Dec 22 | Dec 14 | Dec 10 | Dec 6 | Nov 28 |
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 2 | Oct 21 | Nov 10 |
| Freeze (32°F) | Oct 17 | Nov 5 | Nov 28 |
| Hard (28°F) | Oct 31 | Nov 24 | Dec 20 |
| Severe (24°F) | Nov 13 | Dec 11 | Jan 29 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 2 | Oct 7 | Oct 13 | Oct 17 | Oct 21 | Oct 26 | Oct 30 | Nov 3 | Nov 10 |
| 32°F | Oct 17 | Oct 24 | Oct 29 | Nov 1 | Nov 5 | Nov 10 | Nov 15 | Nov 21 | Nov 28 |
| 28°F | Oct 31 | Nov 7 | Nov 13 | Nov 19 | Nov 24 | Nov 28 | Dec 3 | Dec 10 | Dec 20 |
| 24°F | Nov 13 | Nov 23 | Nov 29 | Dec 5 | Dec 11 | Dec 20 | Dec 26 | Jan 4 | Jan 29 |
| 20°F | Nov 25 | Dec 1 | Dec 7 | Dec 12 | Dec 20 | Dec 26 | Jan 2 | Jan 24 | Feb 12 |
| 16°F | Nov 27 | Dec 2 | Dec 7 | Dec 10 | Dec 15 | Dec 22 | Dec 31 | Jan 16 | Feb 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: Longview, Wa, about 10.7 miles away@if(!empty($station['elevation_ft'])), at 12 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 Castle Rock, WA?
On average, the last spring frost (32°F) around Castle Rock, WA is about Apr 8. In cooler years it can run later, so for a safer bet many gardeners wait until Mar 11.
When is the first frost in the fall?
The first fall frost around Castle Rock, WA typically arrives about Nov 5. 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 8 on average, or Mar 11 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 210 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 98611 Planting calendar → Washington frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026