When does it frost where you garden?
Pick your town below. You'll get your frost dates as a range — because that's the honest way to give them — and the planting calendar that follows from them.
Find your garden
Grouped by climate band, not by county — the bands are what actually govern frost.
Salish Sea lowlands
Within a few miles of Puget Sound, the Strait, or the Salish Sea shoreline, on flat or gently sloping ground. Marine air moderates both ends of the season. This is the mildest inland band.
Willamette Valley
The Oregon valley floor from Portland south through Eugene, plus the Vancouver–Camas side of the Columbia. Warmer summers than Puget Sound, but valley floors radiate heat away on clear nights and frost later in spring.
Coast
Open to the Pacific — the Oregon and Washington coast, Willapa Bay, Grays Harbor, the outer Olympic Peninsula. Frost is mild and infrequent. Your constraint isn't cold, it's summer heat that never quite arrives.
Foothills & cold-air pockets
River valleys, the Cascade and Olympic foothills, the south Sound prairie country, and any bowl where cold air settles. Olympia is the classic example. Same zone label as Seattle, frost dates seven weeks apart.
- Cold air runs downhill and pools. If your garden sits at the bottom of a slope, in a hollow, or behind a solid fence that dams the flow, treat yourself as one band colder.
- A south or west wall buys you weeks. Masonry and siding hold the day's heat and release it overnight.
- Bare, open ground frosts harder. New subdivisions with no canopy and thin soil lose heat fast on clear nights.
- Water moderates. Right on the shoreline, frost comes later in fall and leaves earlier in spring.
- Soil temperature is its own clock. It lags frost by weeks in a maritime climate, which is why some dates below are tied to the soil instead.
Your frost dates
Adjust for your actual yard
Station numbers describe an airport field. Yours is not an airport field. These are rules of thumb, and the page shows you exactly what it shifted.
How to read these dates
This is climate history, not a forecast. Every date here comes from thirty years of records — 1991 through 2020 — at the nearest long-record weather station. It describes what usually happened, not what will happen this spring. No one can tell you your actual last frost until it has already passed.
Two dates, because one would be a guess wearing a fact's clothes. The typical date is the halfway mark: in half of years frost came later. The safe date is the one only about one year in ten beats. Which you use depends on what you are risking. The safe date is what you plan an event around. The typical date is what you'd gamble a flat of cosmos on, knowing you might re-sow.
Frost can form above freezing. On a clear, still night, leaf surfaces and low ground drop several degrees below the air temperature at thermometer height. A reading of 35 or 36 can still leave frost on dahlia foliage. If the forecast is close and the sky is clear, cover things.
Zone numbers won't tell you this. Zones describe average winter lows, not frost timing. Seattle and Olympia are both called zone 8b, and their median last frosts sit about seven weeks apart. That gap is the whole reason this page exists.
Your yard has the final say. A slope, a fence, a wall, a hollow, a strip of bare soil — any of these can move your real dates by two weeks in either direction. Keep your own record for a few years. It will beat any station.
What that means for planting
Some of these follow your frost dates directly. Others follow soil temperature, which in a maritime climate lags frost by weeks — those are marked and given as regional windows rather than calculated dates. Pretending otherwise is how gardeners lose dahlias.
Want this as a printable card?
One page for your band — both frost dates, the season length, and the planting windows. Sized for a potting bench or the inside of a shed door. We'll send it to you, and then a note a few times a year when the bloom calendar grows.
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This is one page of an eighty-page book
The PNW Cutting Garden Planner takes the same four bands and runs them through twenty-five flowers — each one photographed, each with its own sowing, cutting and vase-life notes, twelve monthly task pages, a bloom chart, and a directory of the growers and gardens worth the drive.
See the planner Updates & source directory