Data: 2023 USDA zones (PRISM/OSU) · NOAA 1991–2020 normals · updated Oct 30, 2026

Planting zone for 99133 — Grand Coulee, WA

ZIP code 99133 (Grand Coulee, Grant County) is in USDA zone 7a: the coldest winter night averages 0 to 5 °F. The median last spring frost is April 22 and the first fall frost October 21.

Where ZIP 99133 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 22

First frostOct 21

2012 zone6b

Was 6b 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 7a means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Grand Coulee, 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 Grand Coulee, WA

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostApril 22median — 50% chance of a later frost

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

First fall frostOctober 21median — 10% chance by Oct 6

Growing season180 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 1 and returns around November 1.

From the NOAA station Coulee Dam 1 Sw, WA — 7 miles away, elevation 1,719 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 99133

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 11 – Mar 25

SpinachSow outdoors · Mar 11 – Apr 1

Broccoli, cabbageStart indoors · Feb 11 – Feb 25

Broccoli, cabbageTransplant · Apr 1 – Apr 15

Onion setsPlant outdoors · Mar 25 – Apr 8

PotatoesPlant outdoors · Apr 1 – Apr 15

LettuceSow outdoors · Mar 25 – Apr 8

Carrots, beetsSow outdoors · Apr 1 – Apr 15

TomatoesStart indoors · Feb 25 – Mar 11

TomatoesTransplant · Apr 29 – May 13

Peppers, eggplantStart indoors · Feb 11 – Feb 25

Peppers, eggplantTransplant · May 6 – May 20

BeansSow outdoors · Apr 29 – May 13

Sweet cornSow outdoors · Apr 29 – May 13

Cucumbers, squashSow outdoors · Apr 29 – May 13

Fall lettuce, spinachSow outdoors · Aug 26 – Sep 9

GarlicPlant cloves · Oct 7 – Nov 11

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 22) and first fall frost (Oct 21) 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 99133 came on Apr 1 — 7 days earlier than the 1991–2020 average (Apr 8).

average
Apr 82026
Apr 1

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 Grand Coulee, WA.

Soil in Grand Coulee, WA

The soil mapped at the center of ZIP 99133 is Conconully — ashy sandy loam, well drained.

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

pH6.5neutral; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter2%moderate

Hydrologic groupBwater soaks in moderately

Farmland classNot prime farmlandUSDA classification

Map unit: Conconully-Swakane-Rock outcrop complex, 15 to 30 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 99133; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Grand Coulee, WA

Summer high88 °Faverage high, July

Winter low23 °Faverage low, January

Hot days33days a year at 90 °F or more

Freezing nights120nights a year at 32 °F or less

Growing degree days2,717base 50 °F — the season’s usable heat

Longest day16 h 03 mindaylight on June 21

Shortest day8 h 22 mindaylight on December 21

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

Precipitation11.1 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: Coulee Dam 1 Sw, WA (7 mi away); precipitation: Coulee Dam 1 Sw, WA (7 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

991247b

Elmer City, WA · 8 mi

991167a

Coulee Dam, WA · 9 mi

991237a

Electric City, WA · 9 mi

988306b

Mansfield, WA · 20 mi

Bridgeport, WA · 22 mi

991407a

Keller, WA · 24 mi

Washington planting zones →

Questions about 99133

What planting zone is ZIP code 99133?

ZIP code 99133 (Grand Coulee, 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 Grand Coulee, WA?

The median last spring frost (32 °F) near 99133 is April 22; after May 7 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Coulee Dam 1 Sw station.

When is the first frost in Grand Coulee, WA?

The median first fall frost near 99133 is October 21, giving a median frost-free growing season of 180 days.

When should I plant tomatoes in 99133?

Start tomato seeds indoors around Feb 25 – Mar 11 and set transplants outside around Apr 29 – May 13, one to three weeks after the median last frost.

How much rain and snow does 99133 get?

About 11.1 inches of precipitation a year (NOAA 1991–2020 normals, Coulee Dam 1 Sw station).

How hot do summers get in Grand Coulee, WA?

The average high peaks at 88 °F in July, with about 33 days a year at 90 °F or more.

What kind of soil does 99133 have?

The USDA soil survey maps Conconully at the center of ZIP 99133: ashy sandy loam, well drained, pH about 6.5 (neutral).

Did spring come early in Grand Coulee, WA in 2026?

Spring leaf-out near 99133 came on Apr 1 in 2026, 7 days earlier than the 1991–2020 average (Apr 8), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Grand Coulee, WA?

Long-day onions: the longest day near 99133 is 16 h 03 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99133 change?

Yes. The 2012 USDA map put 99133 in zone 6b; the 2023 map puts it in zone 7a. The newer map uses 1991–2020 data and more weather stations.