Frost dates Washington Seattle

Frost dates in Seattle, Washington

Last spring frost Mar 13 First fall frost Nov 17 NOAA 1991-2020

The average last spring frost in Seattle is Mar 13 and the average first fall frost is Nov 17, measured at SEATTLE BOEING FLD, about 5 miles from the city centre. Below: how sure those dates are, and what to start, sow and set out each week.

Average last spring frostMar 1332°F, 50% probability
Average first fall frostNov 1732°F, 50% probability
Days between them249average frost-free season
How sure is that date? NOAA probability levels for a 32°F freeze
ProbabilityFreeze still comes after (spring)First freeze has come by (fall)
90%Feb 20Dec 6
50%Mar 13Nov 17
10%Apr 1Nov 1

Read it like this: in half of years the last 32°F freeze of spring comes after Mar 13, and in 1 year in 10 there is still a freeze after Apr 1. In 1 year in 10 the first fall freeze arrives before Nov 1.

Measured at: SEATTLE BOEING FLD, WA (NOAA station USW00024234), about 5 miles away at 20 ft, 18 years of record in 1991-2020.

Other stations nearby, for comparison:

  • SEATTLE SAND PT WSFO, WA (NOAA station USW00094290), about 7 miles away at 60 ft, 29 years of record in 1991-2020: last spring frost Mar 8, first fall frost Nov 23
  • RENTON MUNI AP, WA (NOAA station USW00094248), about 10 miles away at 29 ft, 19 years of record in 1991-2020: last spring frost Mar 13, first fall frost Nov 16

Seed-starting schedule for Seattle, WA

Counted from a last frost date of Mar 13 (the average: a freeze comes later than this in half of years).

  1. Week of Dec 514 weeks before last frost
    • Start seeds indoorsLeekDec 5 to Dec 19
    • Start seeds indoorsOnionDec 5 to Dec 19
  2. Week of Dec 1213 weeks before last frost
    • Start seeds indoorsParsleyDec 12 to Dec 19
  3. Week of Dec 1912 weeks before last frost
    • Start seeds indoorsCeleryDec 19 to Jan 2
    • Start seeds indoorsSpinachDec 19 to Jan 2
  4. Week of Jan 210 weeks before last frost
    • Start seeds indoorsBroccoliJan 2 to Jan 16
    • Start seeds indoorsBrussels sproutJan 2 to Jan 16
    • Start seeds indoorsCabbageJan 2 to Jan 16
    • Start seeds indoorsKaleJan 2 to Jan 16
    • Start seeds indoorsKohlrabiJan 2 to Jan 16
  5. Week of Jan 99 weeks before last frost
    • Start seeds indoorsLettuceJan 9 to Jan 16
  6. Week of Jan 168 weeks before last frost
    • Start seeds indoorsCauliflowerJan 16 to Jan 30
    • Start seeds indoorsEggplantJan 16 to Jan 30
    • Start seeds indoorsPepperJan 16 to Jan 30
    • Start seeds indoorsSwiss chardJan 16 to Jan 30
  7. Week of Jan 237 weeks before last frost
    • Start seeds indoorsTomatoJan 23 to Feb 6
  8. Week of Jan 306 weeks before last frost
    • Start seeds indoorsBasilJan 30 to Feb 13
    • Set transplants outSpinachJan 30 to Feb 20
  9. Week of Feb 134 weeks before last frost
    • Sow seed outdoorsRadishFeb 13 to Feb 27
    • Sow seed outdoorsSwiss chardfrom Feb 13
    • Sow seed outdoorsTurnipFeb 13 to Feb 27
    • Set transplants outBroccoliFeb 13 to Feb 27
    • Set transplants outBrussels sproutFeb 13 to Feb 27
    • Set transplants outCabbagefrom Feb 13
    • Set transplants outKalefrom Feb 13
    • Set transplants outKohlrabifrom Feb 13
    • Set transplants outLeekfrom Feb 13
    • Set transplants outLettuceFeb 13 to Feb 20
    • Set transplants outOnionfrom Feb 13
  10. Week of Feb 203 weeks before last frost
    • Start seeds indoorsCucumberFeb 20 to Feb 27
    • Set transplants outParsleyFeb 20 to Feb 27
  11. Week of Feb 272 weeks before last frost
    • Start seeds indoorsMelonFeb 27 to Mar 6
    • Start seeds indoorsPumpkinFeb 27 to Mar 6
    • Start seeds indoorsSummer squashFeb 27 to Mar 6
    • Start seeds indoorsWinter squashFeb 27 to Mar 6
    • Start seeds indoorsZucchiniFeb 27 to Mar 6
    • Plant seed potatoes outdoorsPotatoFeb 27 to Mar 6
    • Set transplants outCauliflowerfrom Feb 27
    • Set transplants outSwiss chardfrom Feb 27
  12. Week of Mar 13Last frost week
    • Sow seed outdoorsBeanfrom Mar 13
    • Sow seed outdoorsParsnipfrom Mar 13
    • Set transplants outCeleryfrom Mar 13
  13. Week of Mar 201 week after last frost
    • Plant slips outdoorsSweet potatoMar 20 to Mar 27
    • Set transplants outCucumberMar 20 to Mar 27
    • Set transplants outTomatoMar 20 to Mar 27
  14. Week of Mar 272 weeks after last frost
    • Set transplants outBasilfrom Mar 27
    • Set transplants outEggplantMar 27 to Apr 3
    • Set transplants outMelonfrom Mar 27
    • Set transplants outPepperfrom Mar 27
    • Set transplants outPumpkinfrom Mar 27
    • Set transplants outSummer squashfrom Mar 27
    • Set transplants outWinter squashfrom Mar 27
    • Set transplants outZucchinifrom Mar 27

Not in the city centre? Look up your own ZIP code

More in Washington

Where the numbers come from

Sources and method

Frost dates. U.S. Climate Normals 2020: U.S. Annual/Seasonal Climate Normals (1991-2020), NOAA National Centers for Environmental Information (Palecki, Durre, Applequist, Arguez and Lawrimore, 2021). These are 30-year station statistics for 1991 to 2020. "Frost" here means an air temperature of 32°F or lower at the station. We use 6,539 stations that have at least 10 years of record and a published date; 176 more are stations where a freeze is too rare for NOAA to date, and 180 are stations cold enough to have frost risk all year.

Probability level. The headline dates are NOAA's 50% level: in half of years the last spring freeze comes later than that date, and in half of years the first fall freeze comes earlier. The 10% and 90% levels are shown next to them. For tender plants, the 10% spring date is the safer one to plan from: a freeze follows it in only 1 year in 10.

Which station. Your ZIP code is matched to the nearest of those stations by straight-line distance from the ZIP code's centre point (GeoNames, geonames.org, CC BY 4.0; 40,979 ZIP codes in the 50 states and DC). Nearest is not always most alike: a station on a hill, in a valley or by the water can differ from your garden by a week or more. That is why the station's name, distance and elevation are shown with every result, along with two more stations nearby. NOAA makes the same point: the normals are limited between stations as distance grows horizontally and vertically.

Seed-starting offsets. Growing Vegetables: When to Plant Your Vegetable Garden, a fact sheet from University of New Hampshire Extension. It gives each crop's weeks from seed to transplant and when it is safe to set out or sow relative to the last frost. The method is theirs too: take the planting date and count back the seed-to-transplant weeks. Where the fact sheet gives a range of planting dates, the start-indoors dates count back from the earliest one. The figures used, as the fact sheet states them:

  • Basil: Seed to transplant 6-8 weeks; set out 2 weeks after last frost.
  • Bean: Plant seed in garden after last frost.
  • Broccoli: Seed to transplant 4-6 weeks; set out 2-4 weeks before last frost.
  • Brussels sprout: Seed to transplant 4-6 weeks; set out 2-4 weeks before last frost.
  • Cabbage: Seed to transplant 4-6 weeks; set out 4 weeks before last frost.
  • Cauliflower: Seed to transplant 4-6 weeks; set out 2 weeks before last frost.
  • Celery: Seed to transplant 10-12 weeks; set out after last frost.
  • Cucumber: Seed to transplant 3-4 weeks; set out 1-2 weeks after last frost.
  • Eggplant: Seed to transplant 8-10 weeks; set out 2-3 weeks after last frost.
  • Kale: Seed to transplant 4-6 weeks; set out 4 weeks before last frost.
  • Kohlrabi: Seed to transplant 4-6 weeks; set out 4 weeks before last frost.
  • Leek: Seed to transplant 8-10 weeks; set out 4 weeks before last frost.
  • Lettuce: Seed to transplant 4-5 weeks; set out 3-4 weeks before last frost.
  • Melon: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.
  • Onion: Seed to transplant 8-10 weeks; set out 4 weeks before last frost.
  • Parsley: Seed to transplant 9-10 weeks; set out 2-3 weeks before last frost.
  • Parsnip: Plant seed in garden after last frost.
  • Pepper: Seed to transplant 8-10 weeks; set out 2 weeks after last frost.
  • Potato: Plant seed potatoes in garden 1-2 weeks before last frost.
  • Pumpkin: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.
  • Radish: Plant seed in garden 2-4 weeks before last frost.
  • Spinach: Seed to transplant 4-6 weeks; set out 3-6 weeks before last frost.
  • Summer squash: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.
  • Sweet potato: Plant slips in garden 1-2 weeks after last frost.
  • Swiss chard: Seed to transplant 4-6 weeks; set out 2 weeks before last frost; or plant seed in garden 4 weeks before last frost.
  • Tomato: Seed to transplant 6-8 weeks; set out 1-2 weeks after last frost.
  • Turnip: Plant seed in garden 2-4 weeks before last frost.
  • Winter squash: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.
  • Zucchini: Seed to transplant 3-4 weeks; set out 2 weeks after last frost.

Not on the calendar. The same fact sheet times these by soil temperature, not by frost date, so they get no date here:

  • Pea: as soon as the soil thaws.
  • Beet: when the soil warms to 45°F.
  • Carrot: when the soil warms to 60°F.
  • Corn: when the soil warms to 60°F.
  • Cucumber, pumpkin, summer squash, winter squash, zucchini: direct-sow when the soil warms to 70°F.

Rutabaga is left out: the fact sheet gives it New Hampshire calendar dates, not a frost offset.

The fact sheet was written for New Hampshire. The offsets are relative to the last frost, so they carry to other places with a spring frost, but where winters are mild many cool-season crops are grown in fall and winter instead. Your state's extension service has the local calendar. Dates are 30-year statistics, not a forecast: check the forecast before setting tender plants out.

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