Washington and Oregon hardiness zones: look up your planting zone by ZIP

Find your hardiness zone by ZIP code

Type a Washington or Oregon ZIP code and the tool returns its zone on the 2023 USDA Plant Hardiness Zone Map, the coldest-night temperature band behind that zone, and how to match it to a plant tag. The list is the ZIP file that the PRISM Group at Oregon State University produced for USDA: 708 Washington ZIPs and 473 Oregon ZIPs, built into this page, so nothing you type leaves your browser.

A ZIP gets one zone, but your yard can run colder or warmer than that. USDA notes that blacktop and concrete create small heat islands, while low ground collects cold air as frost pockets. If your garden sits where cold air pools, treat the result as a starting point and lean toward hardier trees.

Zone 8b alone holds 38% of the ZIP codes, and 8b plus 9a hold 60%. Those two half zones take in Seattle, Tacoma, Everett, Bellingham, Vancouver, Portland, Salem, Eugene and Medford, where the coldest night of an average winter falls between 15 and 25°F. Zones 6a through 7b cover another 403 ZIPs, including Spokane, Yakima, Wenatchee, Kennewick, Bend, Klamath Falls and Pendleton.

What a hardiness zone means

USDA builds each zone from the average annual extreme minimum temperature: take the single coldest reading of each winter at a place, then average those lows over 30 years. Full zones are 10°F wide, and each one splits into an "a" half and a warmer "b" half, 5°F apiece. Zone 8b, the most common zone in both states, means the coldest night of the year averaged 15 to 20°F over 1991–2020.

Because the zone is an average of yearly extremes, some winters will go colder than its band. USDA describes the map as the standard for judging which plants are most likely to thrive at a location; for a tree, that means surviving winter cold, and nothing more.

What changed with the 2023 map

USDA released the current map on November 15, 2023, developed jointly by its Agricultural Research Service and Oregon State University's PRISM Climate Group. It averages the winters of 1991–2020, where the 2012 map used 1976–2005, and it draws on more than 13,000 weather stations, up from 7,983 for the 2012 edition.

USDA says about half the country moved into the next warmer half zone and the other half stayed in the same one; its map notes put the typical change at about a quarter zone warmer across much of the country. The developers also caution that zone shifts are not reliable evidence of climate change, because the coldest night of the year swings widely from winter to winter and the new map uses better methods and more stations. If an older plant tag or book lists your town a half zone colder than the lookup above, it may be quoting the 2012 map.

Washington hardiness zones by city

Washington's 708 ZIP codes run from 6a to 9b, and 8b is the most common at 263 ZIPs (37%). Seattle is the simplest case in either state: all 60 ZIP codes that begin with 981 are 9a. Tacoma, Everett, Bellingham and Vancouver are a half zone colder at 8b, and Olympia is 8a.

Source: USDA ARS Plant Hardiness Zone Map 2023, PRISM Group ZIP file (Oregon State University), checked 2026-10-02. One ZIP per city; other ZIPs in the same city can differ.

East of the Cascades the zones are colder. Every ZIP numbered 988 through 994, the range that holds Wenatchee, Yakima, Spokane, Kennewick, Walla Walla and Pullman, falls between 6a and 7b. Spokane itself splits: 21 of the 27 ZIPs that begin with 992 are 7a, and the other 6, including 99223, are 6b. Washington's warmest ZIP is a single 9b, 98590.

Oregon hardiness zones by city, including Portland

Oregon's 473 ZIP codes cover the widest spread, 5b to 9b, and 8b is again the most common at 189 ZIPs (40%). The Willamette Valley cities in the table below, Salem, Corvallis and Eugene, are all 8b, as are Medford and Astoria.

Source: USDA ARS Plant Hardiness Zone Map 2023, PRISM Group ZIP file (Oregon State University), checked 2026-10-02. One ZIP per city; other ZIPs in the same city can differ.

Portland straddles two half zones. Of the 59 ZIP codes that begin with 972, 44 are 9a and 15 are 8b: 97215 is 9a, while 97201 is 8b. Gresham (97030) and Beaverton (97005) are 9a, and Hillsboro (97124) is 8b, so the zone can change from one Portland-area ZIP to the next.

The extremes are small groups. Eleven of the 12 zone 9b ZIP codes in the two states are in Oregon, including Newport's 97365, and Coos Bay is 9a. At the cold end, Bend (97701) and Baker City (97814) are 6b, 27 Oregon ZIPs are 6a, and one ZIP, 97873, is the only 5b in either state.

What zones don't tell you in the Northwest

A hardiness zone is a winter number. USDA's own guidance lists wind, soil type, soil moisture, humidity, pollution, snow and winter sunshine as factors that can decide whether a plant survives, and it singles out warm-season heat and moisture balance as particularly important. In Washington and Oregon, three of those often matter more than the zone: dry summers, heat waves, and winter wind on wet soil.

Sources: zones from the USDA/PRISM 2023 ZIP file; rain from NOAA 1991–2020 monthly normals at Seattle-Tacoma Intl Airport (USW00024233), Olympia Airport (USW00024227), Portland Intl Airport (USW00024229), Salem McNary Field (USW00024232), Eugene Airport (USW00024221) and Spokane Intl Airport (USW00024157); highs from NOAA Storm Events Database narratives for June 26–30, 2021 (Seattle, Salem and Eugene values are for the city area). Checked 2026-10-02.

Dry summers

West of the Cascades, most rain falls in the cool season. At Seattle-Tacoma airport, 75% of the 39.34-inch annual normal falls from October through March, and July and August together bring 1.57 inches; Salem gets 0.64 inches in those two months. OSU Extension warns that people underestimate how much water a newly planted tree needs, and gives ten gallons a week as a good baseline for many large, mature trees in dry weather.

Heat waves

The late-June 2021 heat wave set all-time records across both states. NOAA's Storm Events Database records 116°F at Portland International Airport, 110°F at the Olympia airport, 109°F at Spokane International Airport and an all-time high of 108°F for the Seattle area. Those places sit in zones 7a to 9a, and nothing in a zone number warns about days like that.

Wind and wet winter soil

NOAA's Storm Events Database holds 1,201 high-wind reports for Washington and Oregon from 2016 through 2025, and 89% of them came between October and March, the same months that bring most of the year's rain. The reports are rows in a database, not separate storms, and they don't count tree failures. Zone ratings also say nothing about drainage, and ISA notes that many urban landscape soils lack the drainage and pore space roots need to grow.

Central Oregon's short season

Bend is 6b, but OSU Extension calls a single zone "really oversimplified" for Central Oregon's microclimates. Clear, sunny weather there brings radiational cooling that can produce frost at any time of year, and OSU lists growing seasons of 80–90 days for Bend and Redmond and 70–80 for La Pine. OSU also points out that the climate zones in the popular Sunset Western Garden Book are a different system from USDA hardiness zones and don't appear on plant tags or in catalogs.

How to use your zone when you choose a tree

1. Start with your ZIP resultNote the zone and its coldest-night band. If your yard is a low spot where cold air settles, lean toward trees rated for a colder zone.
2. Read the coldest zone on the tagA tree suits your winters if the coldest zone on its tag is your zone or a lower number. A tree rated to zone 7 is fine for winter in 8b; one rated only to zone 9 is a gamble in Spokane's 7a.
3. Plan summer water separatelyThe zone won't tell you how dry July gets. Budget water for a new tree's first summers; the schedule is in the guide to the best time to plant trees in the Pacific Northwest.
4. Check mature size against lines and the houseISA's planting zones keep trees within 15 feet of distribution lines to 20 feet tall at maturity, trees 15 to 50 feet away to 40 feet, and large species 50 feet or more away. The utility tree trimming pages show who trims near lines, and the too-close-to-the-house guide covers spacing from walls and roofs.
5. Plant in fall west of the CascadesOSU Extension calls fall planting "a counterintuitive but useful tool" for avoiding stress in newly planted trees. Sea-Tac's normal rain jumps from 1.61 inches in September to 3.91 in October.

For specific trees, the privacy tree comparison sorts Northwest evergreens by mature size and summer water, the Japanese maple care guide covers siting and watering, and Emerald Green vs Green Giant arborvitae compares the two hedge cultivars. Species pages for Douglas fir, western redcedar and bigleaf maple are under trees of Washington and Oregon yards.