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

Planting zone for 98188 — Seattle, WA

ZIP code 98188 (Seattle, King County) is in USDA zone 9a: the coldest winter night averages 20 to 25 °F. The median last spring frost is March 2 and the first fall frost November 23.

Where ZIP 98188 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.

Zone9a20 to 25 °F

Coldest night−6.7 to −3.9 °C

Last frostMar 2

First frostNov 23

2012 zone8b

Was 8b on the 2012 map — half a zone warmer now. The zone is the one at the center of the ZIP code; hilly ZIPs can span two zones. What zone 9a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Seattle, WA…

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 Seattle, WA

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMarch 2median — 50% chance of a later frost

Safe for tender plantsMarch 23only 10% chance of frost after

First fall frostNovember 23median — 10% chance by Nov 6

Growing season266 daysfrost-free, median

A hard freeze (28 °F) usually ends around February 4 and returns around December 10.

From the NOAA station Seattle Tacoma Intl Airport, WA — 2 miles away, elevation 371 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 98188

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Jan 19 – Feb 2

SpinachSow outdoors · Jan 19 – Feb 9

Broccoli, cabbageStart indoors · Dec 22 – Jan 5

Broccoli, cabbageTransplant · Feb 9 – Feb 23

Onion setsPlant outdoors · Feb 2 – Feb 16

PotatoesPlant outdoors · Feb 9 – Feb 23

LettuceSow outdoors · Feb 2 – Feb 16

Carrots, beetsSow outdoors · Feb 9 – Feb 23

TomatoesStart indoors · Jan 5 – Jan 19

TomatoesTransplant · Mar 9 – Mar 23

Peppers, eggplantStart indoors · Dec 22 – Jan 5

Peppers, eggplantTransplant · Mar 16 – Mar 30

BeansSow outdoors · Mar 9 – Mar 23

Sweet cornSow outdoors · Mar 9 – Mar 23

Cucumbers, squashSow outdoors · Mar 9 – Mar 23

Fall lettuce, spinachSow outdoors · Sep 28 – Oct 12

GarlicPlant cloves · Nov 9 – Dec 14

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Mar 2) and first fall frost (Nov 23) 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 98188 came on Feb 12 — 4 days earlier than the 1991–2020 average (Feb 16).

average
Feb 162026
Feb 12

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).

Native plants for zone 9a in Washington

617 plants native to the lower 48 states, recorded in Washington, and rated by the USDA to survive 20 °F or colder — the bottom of zone 9a. Each links to its USDA PLANTS profile.

Source: USDA, NRCS. 2026. The PLANTS Database (plants.usda.gov), National Plant Data Team — state distribution, native status and the “Temperature, Minimum” characteristic. Check light, moisture and soil needs before buying; local nurseries and your state native plant society can confirm what thrives in Seattle, WA.

Soil in Seattle, WA

The soil mapped at the center of ZIP 98188 is Alderwood — gravelly sandy loam, moderately well drained. Much of the area is built over (urban land); this is the natural soil underneath.

TextureGravelly sandy loamdrains and warms fast; dries out and needs more feeding

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

DrainageModerately well drainednatural drainage class

Organic matter9%high

Hydrologic groupAwater soaks in fast

Farmland classNot prime farmlandUSDA classification

Map unit: Urban land-Alderwood complex, 5 to 12 percent slopes.

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 98188; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Seattle, WA

Summer high78 °Faverage high, August

Winter low37 °Faverage low, December

Hot days4days a year at 90 °F or more

Freezing nights25nights a year at 32 °F or less

Growing degree days2,324base 50 °F — the season’s usable heat

Longest day15 h 58 mindaylight on June 21

Shortest day8 h 27 mindaylight on December 21

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

Precipitation39.3 inper year, rain and melted snow

Snowfall6 inper year; 4 days with snow on the ground

Average high and low, by month

Precipitation by month inches · ❄ = snowfall

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Seattle Tacoma Intl Airport, WA (2 mi away); precipitation: Seattle Tacoma Intl Airport, WA (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 9a.

All 59 ZIP codes in Seattle → · Washington planting zones →

Questions about 98188

What planting zone is ZIP code 98188?

ZIP code 98188 (Seattle, WA) is in USDA hardiness zone 9a on the 2023 map: the coldest night of an average winter reaches 20 to 25 °F (−6.7 to −3.9 °C).

When is the last frost in Seattle, WA?

The median last spring frost (32 °F) near 98188 is March 2; after March 23 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Seattle Tacoma Intl Airport station.

When is the first frost in Seattle, WA?

The median first fall frost near 98188 is November 23, giving a median frost-free growing season of 266 days.

When should I plant tomatoes in 98188?

Start tomato seeds indoors around Jan 5 – Jan 19 and set transplants outside around Mar 9 – Mar 23, one to three weeks after the median last frost.

How much rain and snow does 98188 get?

About 39.3 inches of precipitation a year and 6 inches of snowfall (NOAA 1991–2020 normals, Seattle Tacoma Intl Airport station).

How hot do summers get in Seattle, WA?

The average high peaks at 78 °F in August, with about 4 days a year at 90 °F or more.

What kind of soil does 98188 have?

The USDA soil survey maps Alderwood at the center of ZIP 98188: gravelly sandy loam, moderately well drained, pH about 5.8 (moderately acidic).

Did spring come early in Seattle, WA in 2026?

Spring leaf-out near 98188 came on Feb 12 in 2026, 4 days earlier than the 1991–2020 average (Feb 16), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Seattle, WA?

Long-day onions: the longest day near 98188 is 15 h 58 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 98188 change?

Yes. The 2012 USDA map put 98188 in zone 8b; the 2023 map puts it in zone 9a. The newer map uses 1991–2020 data and more weather stations.