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

Planting zone for 99020 — Marshall, WA

ZIP code 99020 (Marshall, Spokane County) is in USDA zone 6b: the coldest winter night averages −5 to 0 °F. The median last spring frost is April 26 and the first fall frost October 12.

Where ZIP 99020 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 frostApr 26
First frostOct 12
2012 zone6b

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 6b means →

Frost forecast — next 7 nights

live from the National Weather Service

Loading the forecast for Marshall, 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 Marshall, WA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 26median — 50% chance of a later frost
Safe for tender plantsMay 10only 10% chance of frost after
First fall frostOctober 12median — 10% chance by Sep 29
Growing season168 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 6 and returns around October 23.

From the NOAA station Spokane Intl Airport, WA — 4 miles away, elevation 2,352 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 99020

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 15 – Mar 29
SpinachSow outdoors · Mar 15 – Apr 5
Broccoli, cabbageStart indoors · Feb 15 – Mar 1
Broccoli, cabbageTransplant · Apr 5 – Apr 19
Onion setsPlant outdoors · Mar 29 – Apr 12
PotatoesPlant outdoors · Apr 5 – Apr 19
LettuceSow outdoors · Mar 29 – Apr 12
Carrots, beetsSow outdoors · Apr 5 – Apr 19
TomatoesStart indoors · Mar 1 – Mar 15
TomatoesTransplant · May 3 – May 17
Peppers, eggplantStart indoors · Feb 15 – Mar 1
Peppers, eggplantTransplant · May 10 – May 24
BeansSow outdoors · May 3 – May 17
Sweet cornSow outdoors · May 3 – May 17
Cucumbers, squashSow outdoors · May 3 – May 17
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 26) 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 99020 came on Apr 2 — 5 days earlier than the 1991–2020 average (Apr 7).

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.

Trees 31

Alaska cedar75 ft · blooms mid spring · low shade tolerance · to −22 °FAmerican sycamore100 ft · blooms spring · medium shade tolerance · to −34 °Fbalsam poplar80 ft · blooms late spring · high shade tolerance · to −79 °Fbigleaf maple60 ft · blooms mid spring · medium shade tolerance · to −14 °Fblack locust60 ft · blooms spring · high shade tolerance · to −37 °Fboxelder60 ft · blooms early spring · low shade tolerance · to −46 °F

Shrubs 102

alderleaf buckthorn3 ft · blooms late spring · low shade tolerance · to −33 °FAllegheny serviceberry35 ft · blooms early spring · low shade tolerance · to −38 °Falpine laurel1 ft · blooms late spring · low shade tolerance · to −28 °FAmerican plum24 ft · blooms mid spring · high shade tolerance · to −38 °Fantelope bitterbrush6 ft · blooms early spring · medium shade tolerance · to −36 °FBarclay's willow15 ft · high shade tolerance · to −43 °F

Wildflowers & perennials 279

alkali buttercup1 ft · blooms late spring · low shade tolerance · to −38 °Falpine bistort1 ft · blooms mid spring · high shade tolerance · to −38 °Falpine mountainsorrel1 ft · blooms mid summer · medium shade tolerance · to −43 °FAmerican alpine speedwell1 ft · blooms summer · medium shade tolerance · to −28 °FAmerican bistort1.5 ft · blooms mid spring · high shade tolerance · to −38 °FAmerican eelgrass1 ft · blooms mid summer · high shade tolerance · to −33 °F

Grasses 154

Alaska brome5 ft · blooms late spring · low shade tolerance · to −18 °FAlaska oniongrass3 ft · blooms mid spring · low shade tolerance · to −33 °Falkali cordgrass3 ft · blooms late summer · high shade tolerance · to −38 °Falkali sacaton3 ft · blooms mid summer · high shade tolerance · to −38 °Falpine timothy1.4 ft · blooms late spring · medium shade tolerance · to −43 °FAmerican beachgrass2.5 ft · blooms spring · high shade tolerance · to −28 °F

Vines 3

riverbank grape45 ft · blooms late spring · medium shade tolerance · to −33 °Ftrumpet creeper2 ft · blooms summer · high shade tolerance · to −13 °Fwestern white clematis1 ft · blooms mid summer · medium shade tolerance · to −38 °F

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 Marshall, WA.

Soil in Marshall, WA

The soil mapped at the center of ZIP 99020 is Springdale — slightly decomposed plant material, somewhat excessively drained.

TextureSlightly decomposed plant materialtop layer
pH5.0strongly acidic; most vegetables like 6.0–7.0
DrainageSomewhat excessively drainednatural drainage class
Organic matter75%high
Hydrologic groupAwater soaks in fast
Farmland classPrime farmland if irrigatedUSDA classification

Map unit: Springdale gravelly ashy coarse sandy loam, 8 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 99020; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Marshall, WA

Summer high84 °Faverage high, July
Winter low24 °Faverage low, December
Hot days21days a year at 90 °F or more
Freezing nights132nights a year at 32 °F or less
Growing degree days2,313base 50 °F — the season’s usable heat
Longest day15 h 59 mindaylight on June 21
Shortest day8 h 26 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation16.4 inper year, rain and melted snow
Snowfall45 inper year; 48 days with snow on the ground

Average high and low, by month

10°20°30°40°50°60°70°80°90°32 °FJanuary: average high 35 °F, low 25 °F 35°25° JanFebruary: average high 40 °F, low 26 °F 40°26° FebMarch: average high 49 °F, low 32 °F 49°32° MarApril: average high 57 °F, low 37 °F 57°37° AprMay: average high 67 °F, low 45 °F 67°45° MayJune: average high 74 °F, low 51 °F 74°51° JunJuly: average high 84 °F, low 58 °F 84°58° JulAugust: average high 84 °F, low 57 °F 84°57° AugSeptember: average high 74 °F, low 49 °F 74°49° SepOctober: average high 58 °F, low 38 °F 58°38° OctNovember: average high 42 °F, low 30 °F 42°30° NovDecember: average high 34 °F, low 24 °F 34°24° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″January: 1.97 in precipitation, 12.3 in snowfall 2.0❄12 JanFebruary: 1.44 in precipitation, 7.8 in snowfall 1.4❄8 FebMarch: 1.83 in precipitation, 3.9 in snowfall 1.8❄4 MarApril: 1.25 in precipitation, 0.7 in snowfall 1.3❄1 AprMay: 1.55 in precipitation, 0.1 in snowfall 1.6 MayJune: 1.17 in precipitation 1.2 JunJuly: 0.42 in precipitation 0.4 JulAugust: 0.47 in precipitation 0.5 AugSeptember: 0.58 in precipitation, 0.1 in snowfall 0.6 SepOctober: 1.37 in precipitation, 0.5 in snowfall 1.4❄1 OctNovember: 2.06 in precipitation, 6.2 in snowfall 2.1❄6 NovDecember: 2.34 in precipitation, 13.8 in snowfall 2.3❄14 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Spokane Intl Airport, WA (4 mi away); precipitation: Spokane Intl Airport, WA (4 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.

990146b
Four Lakes, WA · 5 mi
992246b
Spokane, WA · 6 mi
992036b
Spokane, WA · 6 mi
990016b
Airway Heights, WA · 7 mi
992047a
Spokane, WA · 7 mi
992107a
Spokane, WA · 7 mi
992117a
Spokane, WA · 7 mi
992147a
Spokane, WA · 7 mi

Washington planting zones →

Questions about 99020

What planting zone is ZIP code 99020?

ZIP code 99020 (Marshall, 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 Marshall, WA?

The median last spring frost (32 °F) near 99020 is April 26; after May 10 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Spokane Intl Airport station.

When is the first frost in Marshall, WA?

The median first fall frost near 99020 is October 12, giving a median frost-free growing season of 168 days.

When should I plant tomatoes in 99020?

Start tomato seeds indoors around Mar 1 – Mar 15 and set transplants outside around May 3 – May 17, one to three weeks after the median last frost.

How much rain and snow does 99020 get?

About 16.4 inches of precipitation a year and 45 inches of snowfall (NOAA 1991–2020 normals, Spokane Intl Airport station).

How hot do summers get in Marshall, WA?

The average high peaks at 84 °F in July, with about 21 days a year at 90 °F or more.

What kind of soil does 99020 have?

The USDA soil survey maps Springdale at the center of ZIP 99020: slightly decomposed plant material, somewhat excessively drained, pH about 5.0 (strongly acidic).

Did spring come early in Marshall, WA in 2026?

Spring leaf-out near 99020 came on Apr 2 in 2026, 5 days earlier than the 1991–2020 average (Apr 7), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Marshall, WA?

Long-day onions: the longest day near 99020 is 15 h 59 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).