Why two frost dates instead of one?

Because one date would be a guess dressed up as a fact. The typical date is the halfway mark — half of years frost later than that. The safe date is the one only about one year in ten beats. Which one you use depends on what you are risking.

Is this a forecast for this year?

No. This is climate history, not a forecast. These dates come from thirty years of records, 1991 to 2020. They describe what usually happens, not what will happen this spring.

Why is Olympia so much later than Seattle when they share a growing zone?

Zone numbers describe winter lows, not frost timing. Olympia sits at the head of a lowland where cold air pools on clear nights, so its median last frost is around April 29 while Seattle-Tacoma's is around March 8 — roughly seven weeks apart in the same zone 8b.

Can frost form above 32 degrees?

Yes. On a clear, still night, plant surfaces and low ground can drop several degrees below the air temperature measured at thermometer height. A reading of 35 or 36 can still leave frost on dahlia leaves.

Free tool · maritime Northwest

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.

Step one

Find your garden

Your town, or the closest one to it

Grouped by climate band, not by county — the bands are what actually govern frost.

Step two

Your frost dates

Last frost in spring

Typical. Half of years, the last frost falls later than this.

Safe date. Only about one year in ten sees frost after this.

First frost in fall

Typical. Half of years, the first frost comes earlier than this.

Early edge. About one year in ten, frost has already arrived by now.

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.

Low spot, valley bottom, or a hollow where cold air settlesShifts spring later and fall earlier by about ten days Against a south or west wall, or a sheltered courtyardBuys about a week at each end Open, exposed site — new subdivision, no tree canopyCosts about a week at each end Right on the water — Sound, Strait, or a large lakeBuys about five days at each end

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.

Step three

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 soil, not frost and given as regional windows rather than calculated dates. Pretending otherwise is how gardeners lose dahlias.

Take it with you

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.

No spam, and nothing sold on. Unsubscribe in one click.

Check your inbox — your card is on the way.

This is one page of an eighty-seven-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

Reference

Frost dates by town, west of the Cascades

The same numbers the tool above gives you, written out for all 216 towns it covers. Every date comes from NOAA/NCEI 1991–2020 climate normals at the nearest long-record station. Typical is the halfway mark — in half of years the frost fell later than this. The safe and early edge dates are the ones only about one year in ten beats. This is climate history, not a forecast.

Towns are grouped by climate band rather than by county, because the bands are what actually govern frost. Seattle and Olympia are both called zone 8b and their median last frosts sit about seven weeks apart.

Salish Sea lowlands — first frost typically November 21, last frost typically March 8

Last frost in spring: Typically March 8. Safe date March 30 — only about one year in ten sees frost after this.
First frost in fall: Typically November 21. Early edge November 3 — about one year in ten, frost has already arrived by then.
Growing season: About 259 frost-free days in a median year.
Reference station: Seattle–Tacoma Airport

57 towns in this band: Allyn, Anacortes, Bainbridge Island, Belfair, Bellevue, Bellingham, Blaine, Bothell, Bremerton, Burien, Burlington, Camano Island, Coupeville, Des Moines, DuPont, Edmonds, Everett, Federal Way, Ferndale, Freeland, Gig Harbor, Hoodsport, Kenmore, Kingston, Kirkland, La Conner, Lake Forest Park, Lakewood, Langley, Lynnwood, Marysville, Mercer Island, Mill Creek, Mount Vernon, Mountlake Terrace, Mukilteo, Newcastle, Normandy Park, Oak Harbor, Port Angeles, Port Ludlow, Port Orchard, Port Townsend, Poulsbo, Redmond, Renton, SeaTac, Seattle, Sequim, Shoreline, Silverdale, Stanwood, Steilacoom, Tacoma, Tukwila, University Place, Vashon.

Willamette Valley — first frost typically October 26, last frost typically April 18

Last frost in spring: Typically April 18. Safe date May 8 — only about one year in ten sees frost after this.
First frost in fall: Typically October 26. Early edge October 8 — about one year in ten, frost has already arrived by then.
Growing season: About 192 frost-free days in a median year.
Reference station: Salem, McNary Field

60 towns in this band: Albany, Amity, Aurora, OR, Beaverton, Brownsville, Camas, Canby, Carlton, Clackamas, Coburg, Cornelius, Corvallis, Cottage Grove, Creswell, Dallas, OR, Damascus, Dundee, Eugene, Forest Grove, Gladstone, Gresham, Happy Valley, Harrisburg, Hillsboro, Hubbard, Independence, OR, Jefferson, OR, Junction City, Keizer, Lake Oswego, Lebanon, OR, McMinnville, Milwaukie, Monmouth, OR, Mount Angel, Newberg, North Plains, Oregon City, Philomath, Portland, Ridgefield, Salem, Scappoose, Sheridan, OR, Sherwood, Silverton, OR, Springfield, OR, St. Helens, Stayton, Sublimity, Tigard, Tualatin, Turner, Vancouver, WA, Veneta, Washougal, West Linn, Wilsonville, Woodburn, Yamhill.

Coast — first frost typically November 9, last frost typically April 1

Last frost in spring: Typically April 1. Safe date April 26 — only about one year in ten sees frost after this.
First frost in fall: Typically November 9. Early edge October 17 — about one year in ten, frost has already arrived by then.
Growing season: About 221 frost-free days in a median year.
Reference station: Astoria Regional Airport

39 towns in this band: Aberdeen, Astoria, Bandon, Brookings, Cannon Beach, Coos Bay, Copalis Beach, Coquille, Depoe Bay, Florence, Forks, Garibaldi, Gearhart, Gold Beach, Grayland, Hoquiam, Ilwaco, Lincoln City, Long Beach, Manzanita, Neah Bay, Nehalem, Newport, OR, North Bend, OR (coast), Ocean Shores, Pacific Beach, Pacific City, Port Orford, Raymond, Reedsport, Rockaway Beach, Seabrook, Seaside, South Bend, Tillamook, Waldport, Warrenton, Westport, Yachats.

Foothills & cold-air pockets — first frost typically October 14, last frost typically April 29

Last frost in spring: Typically April 29. Safe date May 14 — only about one year in ten sees frost after this.
First frost in fall: Typically October 14. Early edge September 29 — about one year in ten, frost has already arrived by then.
Growing season: About 168 frost-free days in a median year.
Reference station: Olympia Airport

60 towns in this band: Amboy, Arlington, Auburn, Battle Ground, Black Diamond, Bonney Lake, Buckley, Carnation, Castle Rock, Centralia, Chehalis, Concrete, Covington, Darrington, Duvall, Eatonville, Elma, Enumclaw, Estacada, Fall City, Falls City, Gold Bar, Graham, Granite Falls, Issaquah, Kelso, Kent, Lacey, Lake Stevens, Longview, Lynden, Maltby, Maple Valley, Molalla, Monroe, WA, Montesano, North Bend, WA (Snoqualmie), Olympia, Orting, Puyallup, Rainier, WA, Roy, Sammamish, Sandy, Sedro-Woolley, Shelton, Snohomish, Snoqualmie, Spanaway, Sultan, Sumner, Sweet Home, Tenino, Toledo, WA, Troutdale, Tumwater, Willamina, Winlock, Woodinville, Yelm.

Towns in the same band share a reference station, so they share these numbers. Your own yard has the final say — a low spot, a warm south wall, an exposed lot or a shoreline can move your real dates by two weeks in either direction. Use the tool above to adjust for yours.