Frost dates Oregon Portland

Frost dates in Portland, Oregon

Last spring frost Feb 25 First fall frost Dec 1 NOAA 1991-2020

The average last spring frost in Portland is Feb 25 and the average first fall frost is Dec 1, measured at PORTLAND KGW-TV, about 1 mile from the city centre. Below: how sure those dates are, and what to start, sow and set out each week.

Average last spring frostFeb 2532°F, 50% probability
Average first fall frostDec 132°F, 50% probability
Days between them279average 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%Jan 24Dec 27
50%Feb 25Dec 1
10%Mar 21Nov 10

Read it like this: in half of years the last 32°F freeze of spring comes after Feb 25, and in 1 year in 10 there is still a freeze after Mar 21. In 1 year in 10 the first fall freeze arrives before Nov 10.

Measured at: PORTLAND KGW-TV, OR (NOAA station USC00356749), about 1 mile away at 159 ft, 24 years of record in 1991-2020.

Other stations nearby, for comparison:

  • PORTLAND INTL AP, OR (NOAA station USW00024229), about 6 miles away at 19 ft, 27 years of record in 1991-2020: last spring frost Mar 13, first fall frost Nov 19
  • VANCOUVER PEARSON AP, WA (NOAA station USW00094298), about 7 miles away at 30 ft, 22 years of record in 1991-2020: last spring frost Mar 29, first fall frost Nov 9

Seed-starting schedule for Portland, OR

Counted from a last frost date of Feb 25 (the average: a freeze comes later than this in half of years).

  1. Week of Nov 1914 weeks before last frost
    • Start seeds indoorsLeekNov 19 to Dec 3
    • Start seeds indoorsOnionNov 19 to Dec 3
  2. Week of Nov 2613 weeks before last frost
    • Start seeds indoorsParsleyNov 26 to Dec 3
  3. Week of Dec 312 weeks before last frost
    • Start seeds indoorsCeleryDec 3 to Dec 17
    • Start seeds indoorsSpinachDec 3 to Dec 17
  4. Week of Dec 1710 weeks before last frost
    • Start seeds indoorsBroccoliDec 17 to Dec 31
    • Start seeds indoorsBrussels sproutDec 17 to Dec 31
    • Start seeds indoorsCabbageDec 17 to Dec 31
    • Start seeds indoorsKaleDec 17 to Dec 31
    • Start seeds indoorsKohlrabiDec 17 to Dec 31
  5. Week of Dec 249 weeks before last frost
    • Start seeds indoorsLettuceDec 24 to Dec 31
  6. Week of Dec 318 weeks before last frost
    • Start seeds indoorsCauliflowerDec 31 to Jan 14
    • Start seeds indoorsEggplantDec 31 to Jan 14
    • Start seeds indoorsPepperDec 31 to Jan 14
    • Start seeds indoorsSwiss chardDec 31 to Jan 14
  7. Week of Jan 77 weeks before last frost
    • Start seeds indoorsTomatoJan 7 to Jan 21
  8. Week of Jan 146 weeks before last frost
    • Start seeds indoorsBasilJan 14 to Jan 28
    • Set transplants outSpinachJan 14 to Feb 4
  9. Week of Jan 284 weeks before last frost
    • Sow seed outdoorsRadishJan 28 to Feb 11
    • Sow seed outdoorsSwiss chardfrom Jan 28
    • Sow seed outdoorsTurnipJan 28 to Feb 11
    • Set transplants outBroccoliJan 28 to Feb 11
    • Set transplants outBrussels sproutJan 28 to Feb 11
    • Set transplants outCabbagefrom Jan 28
    • Set transplants outKalefrom Jan 28
    • Set transplants outKohlrabifrom Jan 28
    • Set transplants outLeekfrom Jan 28
    • Set transplants outLettuceJan 28 to Feb 4
    • Set transplants outOnionfrom Jan 28
  10. Week of Feb 43 weeks before last frost
    • Start seeds indoorsCucumberFeb 4 to Feb 11
    • Set transplants outParsleyFeb 4 to Feb 11
  11. Week of Feb 112 weeks before last frost
    • Start seeds indoorsMelonFeb 11 to Feb 18
    • Start seeds indoorsPumpkinFeb 11 to Feb 18
    • Start seeds indoorsSummer squashFeb 11 to Feb 18
    • Start seeds indoorsWinter squashFeb 11 to Feb 18
    • Start seeds indoorsZucchiniFeb 11 to Feb 18
    • Plant seed potatoes outdoorsPotatoFeb 11 to Feb 18
    • Set transplants outCauliflowerfrom Feb 11
    • Set transplants outSwiss chardfrom Feb 11
  12. Week of Feb 25Last frost week
    • Sow seed outdoorsBeanfrom Feb 25
    • Sow seed outdoorsParsnipfrom Feb 25
    • Set transplants outCeleryfrom Feb 25
  13. Week of Mar 41 week after last frost
    • Plant slips outdoorsSweet potatoMar 4 to Mar 11
    • Set transplants outCucumberMar 4 to Mar 11
    • Set transplants outTomatoMar 4 to Mar 11
  14. Week of Mar 112 weeks after last frost
    • Set transplants outBasilfrom Mar 11
    • Set transplants outEggplantMar 11 to Mar 18
    • Set transplants outMelonfrom Mar 11
    • Set transplants outPepperfrom Mar 11
    • Set transplants outPumpkinfrom Mar 11
    • Set transplants outSummer squashfrom Mar 11
    • Set transplants outWinter squashfrom Mar 11
    • Set transplants outZucchinifrom Mar 11

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

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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