Castle Rock, WA 98611 Frost Dates
98611, near Castle Rock, WA: the frost window
Around 04/08 is the usual last spring frost, about 223 days away. Fall's first freeze usually shows up around 11/05, roughly 210 days after the last spring frost.
The USDA Plant Hardiness Zone Map puts Castle Rock in Zone 8b (15 to 20°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
Stretching the season past the first frost
Castle Rock's growing season runs out in roughly 10 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
How much risk comes with planting early here
04/08 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 03/11 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/02 and only about 1 year in 10 sees frost after that.
Castle Rock against the rest of the dataset
Castle Rock's growing season runs about 210 days, ranking 15,026 of 40,283 US ZIP codes measured here, longest to shortest. Within WA, it ranks 275 of 700.
Learn more
Two guides worth reading on 98611: the frost range, on how to read the range around Castle Rock's dates instead of trusting one, and local microclimates, on what one yard in Castle Rock can differ from the 98611 normal.