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

Planting zone for 98603 — Ariel, WA

ZIP code 98603 (Ariel, Cowlitz County) is in USDA zone 8b: the coldest winter night averages 15 to 20 °F. The median last spring frost is April 1 and the first fall frost November 18.

Where ZIP 98603 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 1

First frostNov 18

2012 zone8a

Was 8a 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 8b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Ariel, 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 Ariel, WA

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostApril 1median — 50% chance of a later frost

Safe for tender plantsMay 2only 10% chance of frost after

First fall frostNovember 18median — 10% chance by Oct 29

Growing season227 daysfrost-free, median

A hard freeze (28 °F) usually ends around February 22 and returns around December 7.

From the NOAA station Cougar 6 E, WA — 10 miles away, elevation 659 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 98603

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Feb 18 – Mar 4

SpinachSow outdoors · Feb 18 – Mar 11

Broccoli, cabbageStart indoors · Jan 21 – Feb 4

Broccoli, cabbageTransplant · Mar 11 – Mar 25

Onion setsPlant outdoors · Mar 4 – Mar 18

PotatoesPlant outdoors · Mar 11 – Mar 25

LettuceSow outdoors · Mar 4 – Mar 18

Carrots, beetsSow outdoors · Mar 11 – Mar 25

TomatoesStart indoors · Feb 4 – Feb 18

TomatoesTransplant · Apr 8 – Apr 22

Peppers, eggplantStart indoors · Jan 21 – Feb 4

Peppers, eggplantTransplant · Apr 15 – Apr 29

BeansSow outdoors · Apr 8 – Apr 22

Sweet cornSow outdoors · Apr 8 – Apr 22

Cucumbers, squashSow outdoors · Apr 8 – Apr 22

Fall lettuce, spinachSow outdoors · Sep 23 – Oct 7

GarlicPlant cloves · Nov 4 – Dec 9

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 1) and first fall frost (Nov 18) 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 98603 came on Mar 9 — 23 days earlier than the 1991–2020 average (Apr 1).

average
Apr 12026
Mar 9

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 8b in Washington

614 plants native to the lower 48 states, recorded in Washington, and rated by the USDA to survive 15 °F or colder — the bottom of zone 8b. 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 Ariel, WA.

Soil in Ariel, WA

The soil mapped at the center of ZIP 98603 is Vanson — sandy loam, well drained.

TextureSandy loamdrains and warms fast; dries out and needs more feeding

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

DrainageWell drainednatural drainage class

Organic matter3%moderate

Hydrologic groupBwater soaks in moderately

Farmland classNot prime farmlandUSDA classification

Map unit: Vanson-Hatchet complex, 30 to 65 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 98603; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Ariel, WA

Summer high82 °Faverage high, August

Winter low34 °Faverage low, January

Hot days18days a year at 90 °F or more

Freezing nights35nights a year at 32 °F or less

Growing degree days2,314base 50 °F — the season’s usable heat

Longest day15 h 46 mindaylight on June 21

Shortest day8 h 38 mindaylight on December 21

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

Precipitation102.1 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: Cougar 6 E, WA (10 mi away); precipitation: Yacolt 9.0 N, WA (4 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.

La Center, WA · 16 mi

986228b

Heisson, WA · 16 mi

986048b

Battle Ground, WA · 18 mi

Washington planting zones →

Questions about 98603

What planting zone is ZIP code 98603?

ZIP code 98603 (Ariel, WA) 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 Ariel, WA?

The median last spring frost (32 °F) near 98603 is April 1; after May 2 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Cougar 6 E station.

When is the first frost in Ariel, WA?

The median first fall frost near 98603 is November 18, giving a median frost-free growing season of 227 days.

When should I plant tomatoes in 98603?

Start tomato seeds indoors around Feb 4 – Feb 18 and set transplants outside around Apr 8 – Apr 22, one to three weeks after the median last frost.

How much rain and snow does 98603 get?

About 102.1 inches of precipitation a year (NOAA 1991–2020 normals, Yacolt 9.0 N station).

How hot do summers get in Ariel, WA?

The average high peaks at 82 °F in August, with about 18 days a year at 90 °F or more.

What kind of soil does 98603 have?

The USDA soil survey maps Vanson at the center of ZIP 98603: sandy loam, well drained, pH about 5.8 (moderately acidic).

Did spring come early in Ariel, WA in 2026?

Spring leaf-out near 98603 came on Mar 9 in 2026, 23 days earlier than the 1991–2020 average (Apr 1), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Ariel, WA?

Long-day onions: the longest day near 98603 is 15 h 46 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 98603 change?

Yes. The 2012 USDA map put 98603 in zone 8a; the 2023 map puts it in zone 8b. The newer map uses 1991–2020 data and more weather stations.