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

Planting zone for 99003 — Chattaroy, WA

ZIP code 99003 (Chattaroy, Spokane County) is in USDA zone 6b: the coldest winter night averages −5 to 0 °F. The median last spring frost is May 22 and the first fall frost September 14.

Where ZIP 99003 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.

Zone6b−5 to 0 °F

Coldest night−20.6 to −17.8 °C

Last frostMay 22

First frostSep 14

2012 zone6a

Was 6a 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 6b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Chattaroy, 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 Chattaroy, WA

JanFebMarAprMayJunJulAugSepOctNovDec

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

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

Safe for tender plantsJune 15only 10% chance of frost after

First fall frostSeptember 14median — 10% chance by Aug 28

Growing season112 daysfrost-free, median

A hard freeze (28 °F) usually ends around May 3 and returns around September 29.

From the NOAA station Deer Park Airport, WA — 8 miles away, elevation 2,192 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 99003

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Apr 10 – Apr 24

SpinachSow outdoors · Apr 10 – May 1

Broccoli, cabbageStart indoors · Mar 13 – Mar 27

Broccoli, cabbageTransplant · May 1 – May 15

Onion setsPlant outdoors · Apr 24 – May 8

PotatoesPlant outdoors · May 1 – May 15

LettuceSow outdoors · Apr 24 – May 8

Carrots, beetsSow outdoors · May 1 – May 15

TomatoesStart indoors · Mar 27 – Apr 10

TomatoesTransplant · May 29 – Jun 12

Peppers, eggplantStart indoors · Mar 13 – Mar 27

Peppers, eggplantTransplant · Jun 5 – Jun 19

BeansSow outdoors · May 29 – Jun 12

Sweet cornSow outdoors · May 29 – Jun 12

Cucumbers, squashSow outdoors · May 29 – Jun 12

Fall lettuce, spinachSow outdoors · Jul 20 – Aug 3

GarlicPlant cloves · Aug 31 – Oct 5

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 22) and first fall frost (Sep 14) 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 99003 came on Apr 2 — 7 days earlier than the 1991–2020 average (Apr 9).

average
Apr 92026
Apr 2

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 6b in Washington

581 plants native to the lower 48 states, recorded in Washington, and rated by the USDA to survive −5 °F or colder — the bottom of zone 6b. 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 Chattaroy, WA.

Soil in Chattaroy, WA

The soil mapped at the center of ZIP 99003 is Green Bluff — ashy silt loam, well drained.

TextureAshy silt loama good balance for most vegetables

pH6.4slightly acidic; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter2%moderate

Hydrologic groupBwater soaks in moderately

Farmland classprime farmlandUSDA classification

Map unit: Green Bluff ashy silt loam, 0 to 8 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 99003; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Chattaroy, WA

Summer high84 °Faverage high, July

Winter low21 °Faverage low, January

Hot days22days a year at 90 °F or more

Freezing nights174nights a year at 32 °F or less

Growing degree days1,685base 50 °F — the season’s usable heat

Longest day16 h 02 mindaylight on June 21

Shortest day8 h 23 mindaylight on December 21

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

Precipitation26.7 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: Deer Park Airport, WA (8 mi away); precipitation: Chattaroy 6.3 Ne, WA (2 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.

Deer Park, WA · 11 mi

Newman Lake, WA · 13 mi

992187a

Spokane, WA · 13 mi

Washington planting zones →

Questions about 99003

What planting zone is ZIP code 99003?

ZIP code 99003 (Chattaroy, WA) is in USDA hardiness zone 6b on the 2023 map: the coldest night of an average winter reaches −5 to 0 °F (−20.6 to −17.8 °C).

When is the last frost in Chattaroy, WA?

The median last spring frost (32 °F) near 99003 is May 22; after June 15 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Deer Park Airport station.

When is the first frost in Chattaroy, WA?

The median first fall frost near 99003 is September 14, giving a median frost-free growing season of 112 days.

When should I plant tomatoes in 99003?

Start tomato seeds indoors around Mar 27 – Apr 10 and set transplants outside around May 29 – Jun 12, one to three weeks after the median last frost.

How much rain and snow does 99003 get?

About 26.7 inches of precipitation a year (NOAA 1991–2020 normals, Chattaroy 6.3 Ne station).

How hot do summers get in Chattaroy, WA?

The average high peaks at 84 °F in July, with about 22 days a year at 90 °F or more.

What kind of soil does 99003 have?

The USDA soil survey maps Green Bluff at the center of ZIP 99003: ashy silt loam, well drained, pH about 6.4 (slightly acidic).

Did spring come early in Chattaroy, WA in 2026?

Spring leaf-out near 99003 came on Apr 2 in 2026, 7 days earlier than the 1991–2020 average (Apr 9), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Chattaroy, WA?

Long-day onions: the longest day near 99003 is 16 h 02 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).

Did the zone for 99003 change?

Yes. The 2012 USDA map put 99003 in zone 6a; the 2023 map puts it in zone 6b. The newer map uses 1991–2020 data and more weather stations.