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

Planting zone for 99349 — Mattawa, WA

ZIP code 99349 (Mattawa, Grant County) is in USDA zone 7a: the coldest winter night averages 0 to 5 °F. The median last spring frost is April 23 and the first fall frost October 12.

Where ZIP 99349 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.

Zone7a0 to 5 °F

Coldest night−17.8 to −15 °C

Last frostApr 23

First frostOct 12

2012 zone7a

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 7a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Mattawa, 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 Mattawa, WA

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostApril 23median — 50% chance of a later frost

Safe for tender plantsMay 7only 10% chance of frost after

First fall frostOctober 12median — 10% chance by Oct 1

Growing season172 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 3 and returns around October 24.

From the NOAA station Smyrna, WA — 7 miles away, elevation 561 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 99349

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 12 – Mar 26

SpinachSow outdoors · Mar 12 – Apr 2

Broccoli, cabbageStart indoors · Feb 12 – Feb 26

Broccoli, cabbageTransplant · Apr 2 – Apr 16

Onion setsPlant outdoors · Mar 26 – Apr 9

PotatoesPlant outdoors · Apr 2 – Apr 16

LettuceSow outdoors · Mar 26 – Apr 9

Carrots, beetsSow outdoors · Apr 2 – Apr 16

TomatoesStart indoors · Feb 26 – Mar 12

TomatoesTransplant · Apr 30 – May 14

Peppers, eggplantStart indoors · Feb 12 – Feb 26

Peppers, eggplantTransplant · May 7 – May 21

BeansSow outdoors · Apr 30 – May 14

Sweet cornSow outdoors · Apr 30 – May 14

Cucumbers, squashSow outdoors · Apr 30 – May 14

Fall lettuce, spinachSow outdoors · Aug 17 – Aug 31

GarlicPlant cloves · Sep 28 – Nov 2

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 23) and first fall frost (Oct 12) 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 99349 came on Mar 16 — 3 days earlier than the 1991–2020 average (Mar 19).

average
Mar 192026
Mar 16

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 7a in Washington

590 plants native to the lower 48 states, recorded in Washington, and rated by the USDA to survive 0 °F or colder — the bottom of zone 7a. 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 Mattawa, WA.

Soil in Mattawa, WA

The soil mapped at the center of ZIP 99349 is Quincy — loamy fine sand, somewhat excessively drained.

TextureLoamy fine sanddrains and warms fast; dries out and needs more feeding

pH7.3neutral; most vegetables like 6.0–7.0

DrainageSomewhat excessively drainednatural drainage class

Organic matter0.75%low — add compost

Hydrologic groupAwater soaks in fast

Farmland classFarmland of unique importanceUSDA classification

Map unit: Quincy loamy fine sand, 0 to 15 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 99349; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Mattawa, WA

Summer high93 °Faverage high, July

Winter low26 °Faverage low, January

Hot days54days a year at 90 °F or more

Freezing nights122nights a year at 32 °F or less

Growing degree days3,262base 50 °F — the season’s usable heat

Longest day15 h 51 mindaylight on June 21

Shortest day8 h 32 mindaylight on December 21

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

Precipitation7.5 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: Smyrna, WA (7 mi away); precipitation: Priest Rapids Dam, WA (11 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

993577a

Royal City, WA · 11 mi

Sunnyside, WA · 16 mi

Washington planting zones →

Questions about 99349

What planting zone is ZIP code 99349?

ZIP code 99349 (Mattawa, WA) is in USDA hardiness zone 7a on the 2023 map: the coldest night of an average winter reaches 0 to 5 °F (−17.8 to −15 °C).

When is the last frost in Mattawa, WA?

The median last spring frost (32 °F) near 99349 is April 23; after May 7 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Smyrna station.

When is the first frost in Mattawa, WA?

The median first fall frost near 99349 is October 12, giving a median frost-free growing season of 172 days.

When should I plant tomatoes in 99349?

Start tomato seeds indoors around Feb 26 – Mar 12 and set transplants outside around Apr 30 – May 14, one to three weeks after the median last frost.

How much rain and snow does 99349 get?

About 7.5 inches of precipitation a year (NOAA 1991–2020 normals, Priest Rapids Dam station).

How hot do summers get in Mattawa, WA?

The average high peaks at 93 °F in July, with about 54 days a year at 90 °F or more.

What kind of soil does 99349 have?

The USDA soil survey maps Quincy at the center of ZIP 99349: loamy fine sand, somewhat excessively drained, pH about 7.3 (neutral).

Did spring come early in Mattawa, WA in 2026?

Spring leaf-out near 99349 came on Mar 16 in 2026, 3 days earlier than the 1991–2020 average (Mar 19), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Mattawa, WA?

Long-day onions: the longest day near 99349 is 15 h 51 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).