Portland, Oregon Frost Dates, Growing Season & Hardiness Zone

When is the last frost in Portland?

Expect the last 32°F night by Feb 25 in a typical year; 1 year in 10 still freezes after Mar 21. Cold 36°F nights (frost possible on plants) typically last longer, until around Mar 29. Hard freezes (28°F) typically end sooner, around Jan 31.

Frost risk in Portland drags on well past the typical date. The safer 1-in-10 date (Mar 21) is 24 days later than the typical Feb 25, so protect tender plants set out early on cold nights.

Cool nights hang on after the last freeze: the typical last 36°F night (frost possible on plants in low spots) is around Mar 29, 32 days later than the typical last 32°F night. Frost can form on leaves on clear, calm nights even with the thermometer above freezing.

Is it too early to plant in Portland?

Before Feb 25 the odds of another 32°F night are better than even; after Mar 21 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 Portland?

Half of years get their first 32°F night by Dec 1. In 1 year out of 10, it arrives as early as Nov 10. The first 36°F night (frost possible on plants) typically comes around Nov 12, and the first 28°F hard freeze around Dec 20.

To time a fall crop, count back from the typical first frost (Dec 1) or the safer Nov 10. The planting calendar works it out crop by crop.

How long is Portland's growing season?

A typical year in Portland has 280 days between the last spring and first fall 32°F nights. In about 1 year in 10, there are fewer than 245 days.

With a season this long, you can grow many crops twice: once in spring and again for fall.

Growing degree days measure the heat available for crops to grow. The station averages 2,697 a year (base 50°F).

How does Portland's season compare?

Compared with the 56 U.S. cities with frost dates on this site, this typical frost-free season is longer than in 45 and shorter than in 10.

Growing degree days (base 50°F)

Annual normal: 2,697 GDD (NOAA flag R, 23 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 Portland? (USDA 2023)

Portland is in USDA zone 8b–9a on the 2023 map (15 to 25°F average coldest winter night). Most of the city was 8b on the 2012 map. Comparing the 32 city ZIPs found in both tables: 17 moved up half a zone, 1 moved down half a zone and 14 stayed the same.

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 Portland's frost dates?

No. Zones describe only how cold the coldest winter night gets on average. They don't tell you when frost starts or stops. The frost dates for Portland come from NOAA's 1991–2020 frost probabilities, which the 2023 zone map left untouched. Choose winter-hardy perennials by zone, and schedule planting by frost dates.

Why do Portland frost dates differ between websites?

Some sources list Mar 6 for Portland. That's the 30%-risk date: about 3 years in 10 still see a 32°F night after it. We headline the 50% (median) date, Feb 25.

Mar 21 is the 10%-risk, or 'safer', date. Only about 1 year in 10 has a 32°F night after it.

Mar 29 is the typical (50%) date for a 36°F night (frost possible on plants), not a 32°F freeze. Any site that draws the line at 36°F will show later dates.

Sites also pick different weather stations. Within 25 miles of the city center, the 20 stations that meet our quality rules put the typical (50%) last 32°F frost anywhere from Feb 11 to Apr 29 (table below).

Which weather station is this based on?

Station

Portland KGW-TV (NOAA USC00356749, COOP)

Distance

2.3 mi SW of the city center

Elevation

159 ft; city center 161 ft (USGS), difference −2 ft

Record

NOAA completeness flag R, 24 of 30 years (1991–2020)

Confidence

High (rule)

Confidence: High. The station is close (2.3 miles from the city center), its elevation differs by just 2 ft, and its frost statistics meet our completeness rule (NOAA flag R, 24 of 30 years).

Caveat: these frost statistics carry NOAA's 'R' (representative) flag. They're based on 24 of the 30 years in 1991–2020, with missing months filled in from surrounding stations. The nearest station with a full 'S' (standard) record is Portland International Airport, 4.4 mi away, with a typical last frost of Mar 13.

Portland planting dates at a glance

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

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

Frost dates near Portland

All Oregon cities

Frequently asked questions

What is the average last frost date in Portland?

The typical (median, 50%) last 32°F night in Portland is Feb 25, based on NOAA 1991–2020 normals at Portland KGW-TV. For a safer target, use Mar 21; after that, only about 1 year in 10 still has a freeze.

When is the first frost in Portland?

Typically by Dec 1 for the first 32°F night, though about 1 year in 10 it comes as early as Nov 10. The first 36°F night (frost possible on plants) typically shows up around Nov 12.

What growing zone is Portland, Oregon? Is Portland zone 8 or 9?

Portland is in USDA hardiness zone 8b–9a on the current 2023 map (zone 8–9 for short). On the older 2012 map, most of the city was 8b. That's why older references still say 'zone 8'.

Is it too early to plant in Portland?

For frost-tender plants, yes if it's before Feb 25: until then, the odds of another 32°F night are better than even. Between Feb 25 and Mar 21, the risk falls from 50% to 10%. Cool-season crops like peas and lettuce can go in weeks earlier; see the planting calendar.

What temperature is a killing frost?

It depends on the crop. Tender plants such as tomatoes are killed by a light frost, which CSU Extension describes as 28–32°F; below 28°F is a heavy frost. We show NOAA odds for 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 is when the air reaches 32°F. Frost is ice that forms on surfaces, and on calm, clear nights it can form with the air a few degrees above freezing. So in Portland, the first 36°F night (frost possible on plants) typically comes around Nov 12, before the first 32°F night (Dec 1).

Download & sources

• Add Portland 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 USC00356749); 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.