Seattle, Washington Frost Dates, Growing Season & Hardiness Zone

When is the last frost in Seattle?

Expect the last 32°F night by Mar 8 in a typical year; 1 year in 10 still freezes after Mar 29. Cold 36°F nights (frost possible on plants) typically last longer, until around Apr 4. Hard freezes (28°F) typically end sooner, around Feb 11.

Seattle has a long late-frost tail: 21 days separate the typical date (Mar 8) from the safer 1-in-10 date (Mar 29). If tender plants go out early, be ready to protect them on cold nights.

The typical last 36°F night (frost possible on plants in low spots) comes around Apr 4, 27 days after the typical last 32°F night. On clear, calm nights, frost can form on leaves even when the thermometer reads above freezing.

Is it too early to plant in Seattle?

Before Mar 8 the odds of another 32°F night are better than even; after Mar 29 they are about 1 in 10 or less.

Today's risk is computed in your browser from the same NOAA probability table, shown as the range between the two nearest NOAA probability levels.

When is the first frost in Seattle?

Half of years get their first 32°F night by Nov 23. In 1 year out of 10, it arrives as early as Nov 4. The first 36°F night (frost possible on plants) typically comes around Nov 5, and the first 28°F hard freeze around Dec 11.

For fall crops, count back from Nov 23, or from Nov 4 to be safe. Our planting calendar does the math for each crop.

How long is Seattle's growing season?

A typical year in Seattle has 259 days between the last spring and first fall 32°F nights. In about 1 year in 10, there are fewer than 231 days.

A season this long leaves room for two rounds of many crops, one in spring and one for fall.

Growing degree days measure the heat available for crops to grow. The station averages 2,207 a year (base 50°F).

How does Seattle's season compare?

Among the 56 U.S. cities with frost dates on this site, the typical frost-free season here is longer than in 40 of them and shorter than in 15.

Growing degree days (base 50°F)

Annual normal: 2,207 GDD (NOAA flag S, 28 years). Running total by the end of each month (sum of NOAA daily GDD normals, so the year-end total can differ slightly from the annual normal):

What growing zone is Seattle? (USDA 2023)

On the 2023 USDA map, Seattle is zone 9a (20 to 25°F average coldest winter night). On the 2012 map, most of the city was 8b. Of the 32 city ZIPs listed in both tables, 32 moved up half a zone.

Zones: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed 2026-10-08. Shown as published in the ZIP tables; this page does not show a zone map. Not the official USDA Plant Hardiness Zone Map (official map: planthardiness.ars.usda.gov).

Does the new zone change Seattle's frost dates?

No. Hardiness zones are based only on the average coldest winter temperature. They say nothing about when spring and fall frosts happen. Seattle's frost dates come from NOAA's 1991–2020 frost probabilities, which did not change with the 2023 zone map. Use your zone to pick perennials that will survive winter, and your frost dates to time planting.

Why do Seattle frost dates differ between websites?

You may see Mar 16 given as Seattle's last frost date. That's the 30%-risk date, meaning about 3 years in 10 still have a 32°F night after it. Our headline date is Mar 8, the 50% (median) date.

Mar 29 is the date we call 'safer': it's the 10%-risk date, with a 32°F night after it in only about 1 year in 10.

Apr 4 is the 50% date for a 36°F night (frost possible on plants), not a 32°F freeze. Sites that treat 36°F as the danger line show later dates.

The choice of weather station matters too. The 10 stations within 25 miles of the city center that pass our quality rules give typical (50%) last 32°F frost dates from Mar 2 to Apr 20; see the table below.

Which weather station is this based on?

Station

Seattle Sand Point (NOAA USW00094290, WBAN/ASOS-AWOS)

Distance

6.5 mi NE of the city center

Elevation

60 ft; city center 144 ft (USGS), difference −84 ft

Record

NOAA completeness flag S, 29 of 30 years (1991–2020)

Confidence

High (rule)

Confidence: High. At 6.5 miles from the city center and only 84 ft off in elevation, with frost statistics that meet our completeness rule (NOAA flag S, 29 of 30 years), this station is a close match.

Seattle planting dates at a glance

Balanced dates use the 30%-risk last-frost date as the anchor. The Seattle planting calendar has typical and safe dates, fall planting and a month-by-month list for 26 vegetables.

When to plant tomatoes in Seattle · Fall planting dates for Seattle

Frost dates near Seattle

All Washington cities

Frequently asked questions

What is the average last frost date in Seattle?

The typical (median, 50%) last 32°F night in Seattle is Mar 8, based on NOAA 1991–2020 normals at Seattle Sand Point. For a safer target, use Mar 29; after that, only about 1 year in 10 still has a freeze.

When is the first frost in Seattle?

The first 32°F night typically arrives by Nov 23. About 1 year in 10, it comes as early as Nov 4. A 36°F night (frost possible on plants) typically shows up around Nov 5.

What growing zone is Seattle, Washington? Is Seattle zone 8 or 9?

On the current 2023 USDA map, Seattle is in hardiness zone 9a, part of zone 9. Older references may still say 'zone 8' because most of the city was 8b on the 2012 map.

Is it too early to plant in Seattle?

Before Mar 8, yes, for anything frost-tender. Until then, the odds of another 32°F night are better than even. The risk falls from 50% to 10% between Mar 8 and Mar 29. Peas, lettuce and other cool-season crops can go in weeks earlier; the planting calendar has dates.

What temperature is a killing frost?

For tender crops like tomatoes, a light frost is a killing frost. CSU Extension calls 28–32°F a light frost and below 28°F a heavy frost. Our NOAA odds cover three thresholds: 36°F (frost possible on plants), 32°F (freeze, our headline) and 28°F (hard freeze).

Is first frost the same as first freeze?

Not quite. A 'freeze' means the air reached 32°F. 'Frost' is ice on surfaces, and it can form on calm, clear nights even when the air is a few degrees above freezing. So in Seattle, the first 36°F night (frost possible on plants) typically comes around Nov 5, before the first 32°F night (Nov 23).

Download & sources

• Add Seattle frost & planting dates to your calendar (.ics, 2027)
• Printable planting calendar (PDF)
• How these numbers are calculated

Data: NOAA NCEI U.S. Climate Normals 1991–2020 (annual/seasonal and daily normals, station USW00094290); USDA Plant Hardiness Zone ZIP tables 2023 and 2012 by the PRISM Group, Oregon State University; Census 2020 ZIP/place relationship file; USGS elevation. Long-term odds, not a forecast. Figures and sentences are generated from these data by fixed rules; see the methodology. Last updated 2026-10-08.