Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 29, 2026

Planting zone for 97231 — Portland, OR

ZIP code 97231 (Portland, Multnomah County) is in USDA zone 8b: the coldest winter night averages 15 to 20 °F. The median last spring frost is April 10 and the first fall frost November 2.

Where ZIP 97231 is

Outlined: the ZIP code area · tap the map for the zone at any spot · scroll or pinch to zoom

Not the official USDA Plant Hardiness Zone Map. Zones come from the 2023 USDA hardiness-zone data by the PRISM Group, Oregon State University; we re-mapped and recolored them. The official map is at planthardiness.ars.usda.gov.

Zone8b15 to 20 °F

Coldest night−9.4 to −6.7 °C

Last frostApr 10

First frostNov 2

2012 zone8b

Same zone as on the 2012 map. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 8b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Portland, OR…

Forecast data: National Weather Service (api.weather.gov), public domain. This is not a warning service — for official frost and freeze warnings see weather.gov.

Frost dates in Portland, OR

JanFebMarAprMayJunJulAugSepOctNovDec

Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free

Last spring frostApril 10median — 50% chance of a later frost

Safe for tender plantsMay 1only 10% chance of frost after

First fall frostNovember 2median — 10% chance by Oct 16

Growing season209 daysfrost-free, median

A hard freeze (28 °F) usually ends around March 3 and returns around November 19.

From the NOAA station Scappoose Ind Airport, OR — 6 miles away, elevation 56 ft. NOAA NCEI U.S. Climate Normals 1991–2020, 32 °F threshold. Low spots and valleys can freeze later in spring than the station.

When to plant vegetables in 97231

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Feb 27 – Mar 13

SpinachSow outdoors · Feb 27 – Mar 20

Broccoli, cabbageStart indoors · Jan 30 – Feb 13

Broccoli, cabbageTransplant · Mar 20 – Apr 3

Onion setsPlant outdoors · Mar 13 – Mar 27

PotatoesPlant outdoors · Mar 20 – Apr 3

LettuceSow outdoors · Mar 13 – Mar 27

Carrots, beetsSow outdoors · Mar 20 – Apr 3

TomatoesStart indoors · Feb 13 – Feb 27

TomatoesTransplant · Apr 17 – May 1

Peppers, eggplantStart indoors · Jan 30 – Feb 13

Peppers, eggplantTransplant · Apr 24 – May 8

BeansSow outdoors · Apr 17 – May 1

Sweet cornSow outdoors · Apr 17 – May 1

Cucumbers, squashSow outdoors · Apr 17 – May 1

Fall lettuce, spinachSow outdoors · Sep 7 – Sep 21

GarlicPlant cloves · Oct 19 – Nov 23

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 10) and first fall frost (Nov 2) with the rules of thumb U.S. extension services publish. Cool-season crops take a light frost; warm-season crops do best once the soil is above about 60 °F.

When spring arrived in 2026

In 2026, spring leaf-out near 97231 came on Feb 15 — 5 days earlier than the 1991–2020 average (Feb 20).

average
Feb 202026
Feb 15

JanFebMarAprMayJun

The Spring Index marks the day when accumulated warmth is enough for lilac and honeysuckle to leaf out — a widely used signal that the growing season has started. Source: USA National Phenology Network, www.usanpn.org — Spring Indices, first leaf, 2026 (data as of 2026-09-08) and 30-year average 1991–2020 (CC BY 4.0).

Soil in Portland, OR

The soil mapped at the center of ZIP 97231 is Moag — silty clay loam, very poorly drained.

TextureSilty clay loamholds water and nutrients; slow to drain and warm up

pH5.8moderately acidic; most vegetables like 6.0–7.0

DrainageVery poorly drainedconsider raised beds

Organic matter2%moderate

Hydrologic groupC/Dslow when drained; wet otherwise

Farmland classFarmland of statewide importanceUSDA classification

Map unit: Moag silty clay loam, protected.

Soil Survey Staff, Natural Resources Conservation Service, USDA. Soil Survey Geographic (SSURGO) Database, via Soil Data Access, accessed 2026-10-29. The soil at the center point of ZIP 97231; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Portland, OR

Summer high82 °Faverage high, August

Winter low34 °Faverage low, January

Hot days14days a year at 90 °F or more

Freezing nights61nights a year at 32 °F or less

Growing degree days2,345base 50 °F — the season’s usable heat

Longest day15 h 43 mindaylight on June 21

Shortest day8 h 41 mindaylight on December 21

Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)

Precipitation42.3 inper year, rain and melted snow

Average high and low, by month

Precipitation by month inches

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Scappoose Ind Airport, OR (6 mi away); precipitation: Scappoose Ind Airport, OR (6 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

1 of the 8 nearest ZIP codes are in a different zone — elevation and distance from water change winter lows quickly.

All 59 ZIP codes in Portland → · Oregon planting zones →

Questions about 97231

What planting zone is ZIP code 97231?

ZIP code 97231 (Portland, OR) is in USDA hardiness zone 8b on the 2023 map: the coldest night of an average winter reaches 15 to 20 °F (−9.4 to −6.7 °C).

When is the last frost in Portland, OR?

The median last spring frost (32 °F) near 97231 is April 10; after May 1 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Scappoose Ind Airport station.

When is the first frost in Portland, OR?

The median first fall frost near 97231 is November 2, giving a median frost-free growing season of 209 days.

When should I plant tomatoes in 97231?

Start tomato seeds indoors around Feb 13 – Feb 27 and set transplants outside around Apr 17 – May 1, one to three weeks after the median last frost.

How much rain and snow does 97231 get?

About 42.3 inches of precipitation a year (NOAA 1991–2020 normals, Scappoose Ind Airport station).

How hot do summers get in Portland, OR?

The average high peaks at 82 °F in August, with about 14 days a year at 90 °F or more.

What kind of soil does 97231 have?

The USDA soil survey maps Moag at the center of ZIP 97231: silty clay loam, very poorly drained, pH about 5.8 (moderately acidic).

Did spring come early in Portland, OR in 2026?

Spring leaf-out near 97231 came on Feb 15 in 2026, 5 days earlier than the 1991–2020 average (Feb 20), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Portland, OR?

Long-day onions: the longest day near 97231 is 15 h 43 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).