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

Planting zone for 99402 — Asotin, WA

ZIP code 99402 (Asotin, Asotin County) is in USDA zone 7a: the coldest winter night averages 0 to 5 °F. The median last spring frost is April 6 and the first fall frost October 26.

Where ZIP 99402 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 6
First frostOct 26
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 Asotin, 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 Asotin, WA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostApril 6median — 50% chance of a later frost
Safe for tender plantsApril 26only 10% chance of frost after
First fall frostOctober 26median — 10% chance by Oct 10
Growing season200 daysfrost-free, median

A hard freeze (28 °F) usually ends around March 15 and returns around November 8.

From the NOAA station Lewiston Nez Perce Co. Airport, ID — 19 miles away, elevation 1,437 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 99402

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Feb 23 – Mar 9
SpinachSow outdoors · Feb 23 – Mar 16
Broccoli, cabbageStart indoors · Jan 26 – Feb 9
Broccoli, cabbageTransplant · Mar 16 – Mar 30
Onion setsPlant outdoors · Mar 9 – Mar 23
PotatoesPlant outdoors · Mar 16 – Mar 30
LettuceSow outdoors · Mar 9 – Mar 23
Carrots, beetsSow outdoors · Mar 16 – Mar 30
TomatoesStart indoors · Feb 9 – Feb 23
TomatoesTransplant · Apr 13 – Apr 27
Peppers, eggplantStart indoors · Jan 26 – Feb 9
Peppers, eggplantTransplant · Apr 20 – May 4
BeansSow outdoors · Apr 13 – Apr 27
Sweet cornSow outdoors · Apr 13 – Apr 27
Cucumbers, squashSow outdoors · Apr 13 – Apr 27
Fall lettuce, spinachSow outdoors · Aug 31 – Sep 14
GarlicPlant cloves · Oct 12 – Nov 16
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (Apr 6) and first fall frost (Oct 26) 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 99402 came on Mar 21 — 12 days earlier than the 1991–2020 average (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 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.

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 105

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 282

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 157

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 Asotin, WA.

Soil in Asotin, WA

The soil mapped at the center of ZIP 99402 is Gwinly — very stony silt loam, well drained.

TextureVery stony silt loama good balance for most vegetables
pH7.2neutral; most vegetables like 6.0–7.0
DrainageWell drainednatural drainage class
Organic matter2.5%moderate
Hydrologic groupDwater soaks in very slowly
Farmland classNot prime farmlandUSDA classification

Map unit: Gwinly-Mallory very stony silt loams, 30 to 70 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 99402; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Asotin, WA

Summer high91 °Faverage high, July
Winter low30 °Faverage low, January
Hot days44days a year at 90 °F or more
Freezing nights80nights a year at 32 °F or less
Growing degree days3,143base 50 °F — the season’s usable heat
Longest day15 h 47 mindaylight on June 21
Shortest day8 h 36 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation17.9 inper year, rain and melted snow

Average high and low, by month

20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 42 °F, low 30 °F 42°30° JanFebruary: average high 47 °F, low 32 °F 47°32° FebMarch: average high 55 °F, low 36 °F 55°36° MarApril: average high 62 °F, low 41 °F 62°41° AprMay: average high 72 °F, low 48 °F 72°48° MayJune: average high 79 °F, low 54 °F 79°54° JunJuly: average high 91 °F, low 61 °F 91°61° JulAugust: average high 90 °F, low 60 °F 90°60° AugSeptember: average high 80 °F, low 52 °F 80°52° SepOctober: average high 63 °F, low 42 °F 63°42° OctNovember: average high 49 °F, low 35 °F 49°35° NovDecember: average high 41 °F, low 30 °F 41°30° Dec

Precipitation by month inches

0″1″2″3″January: 1.72 in precipitation 1.7 JanFebruary: 1.41 in precipitation 1.4 FebMarch: 1.75 in precipitation 1.8 MarApril: 1.58 in precipitation 1.6 AprMay: 2.04 in precipitation 2.0 MayJune: 1.71 in precipitation 1.7 JunJuly: 0.69 in precipitation 0.7 JulAugust: 0.57 in precipitation 0.6 AugSeptember: 0.62 in precipitation 0.6 SepOctober: 1.38 in precipitation 1.4 OctNovember: 2.17 in precipitation 2.2 NovDecember: 2.30 in precipitation 2.3 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Lewiston Nez Perce Co. Airport, ID (19 mi away); precipitation: Sourdough Gulch, WA (2 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

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

994017a
Anatone, WA · 10 mi
994037b
Clarkston, WA · 11 mi
993477a
Pomeroy, WA · 18 mi
835017b
Lewiston, ID · 20 mi
991797a
Uniontown, WA · 22 mi
993287a
Dayton, WA · 25 mi
991137a
Colton, WA · 26 mi
835407b
Lapwai, ID · 28 mi

Washington planting zones →

Questions about 99402

What planting zone is ZIP code 99402?

ZIP code 99402 (Asotin, 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 Asotin, WA?

The median last spring frost (32 °F) near 99402 is April 6; after April 26 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Lewiston Nez Perce Co. Airport station.

When is the first frost in Asotin, WA?

The median first fall frost near 99402 is October 26, giving a median frost-free growing season of 200 days.

When should I plant tomatoes in 99402?

Start tomato seeds indoors around Feb 9 – Feb 23 and set transplants outside around Apr 13 – Apr 27, one to three weeks after the median last frost.

How much rain and snow does 99402 get?

About 17.9 inches of precipitation a year (NOAA 1991–2020 normals, Sourdough Gulch station).

How hot do summers get in Asotin, WA?

The average high peaks at 91 °F in July, with about 44 days a year at 90 °F or more.

What kind of soil does 99402 have?

The USDA soil survey maps Gwinly at the center of ZIP 99402: very stony silt loam, well drained, pH about 7.2 (neutral).

Did spring come early in Asotin, WA in 2026?

Spring leaf-out near 99402 came on Mar 21 in 2026, 12 days earlier than the 1991–2020 average (Apr 2), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Asotin, WA?

Long-day onions: the longest day near 99402 is 15 h 47 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).