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

Planting zone for 99161 — Palouse, WA

ZIP code 99161 (Palouse, Whitman County) is in USDA zone 6b: the coldest winter night averages −5 to 0 °F. The median last spring frost is May 6 and the first fall frost September 29.

Where ZIP 99161 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 6

First frostSep 29

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 Palouse, 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 Palouse, WA

JanFebMarAprMayJunJulAugSepOctNovDec

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

Last spring frostMay 6median — 50% chance of a later frost

Safe for tender plantsMay 25only 10% chance of frost after

First fall frostSeptember 29median — 10% chance by Sep 9

Growing season143 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 19 and returns around October 12.

From the NOAA station Pullman 2 Nw, WA — 10 miles away, elevation 2,517 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 99161

JanFebMarAprMayJunJulAugSepOctNovDec

PeasSow outdoors · Mar 25 – Apr 8

SpinachSow outdoors · Mar 25 – Apr 15

Broccoli, cabbageStart indoors · Feb 25 – Mar 11

Broccoli, cabbageTransplant · Apr 15 – Apr 29

Onion setsPlant outdoors · Apr 8 – Apr 22

PotatoesPlant outdoors · Apr 15 – Apr 29

LettuceSow outdoors · Apr 8 – Apr 22

Carrots, beetsSow outdoors · Apr 15 – Apr 29

TomatoesStart indoors · Mar 11 – Mar 25

TomatoesTransplant · May 13 – May 27

Peppers, eggplantStart indoors · Feb 25 – Mar 11

Peppers, eggplantTransplant · May 20 – Jun 3

BeansSow outdoors · May 13 – May 27

Sweet cornSow outdoors · May 13 – May 27

Cucumbers, squashSow outdoors · May 13 – May 27

Fall lettuce, spinachSow outdoors · Aug 4 – Aug 18

GarlicPlant cloves · Sep 15 – Oct 20

Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 6) and first fall frost (Sep 29) 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 99161 came on Mar 23 — 15 days earlier than the 1991–2020 average (Apr 7).

average
Apr 72026
Mar 23

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 Palouse, WA.

Soil in Palouse, WA

The soil mapped at the center of ZIP 99161 is Palouse — silt loam, well drained.

TextureSilt loama good balance for most vegetables

pH6.5neutral; most vegetables like 6.0–7.0

DrainageWell drainednatural drainage class

Organic matter3%moderate

Hydrologic groupBwater soaks in moderately

Farmland classFarmland of statewide importanceUSDA classification

Map unit: Palouse-Thatuna silt loams, 7 to 25 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 99161; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Palouse, WA

Summer high85 °Faverage high, August

Winter low25 °Faverage low, December

Hot days22days a year at 90 °F or more

Freezing nights127nights a year at 32 °F or less

Growing degree days1,983base 50 °F — the season’s usable heat

Longest day15 h 53 mindaylight on June 21

Shortest day8 h 31 mindaylight on December 21

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

Precipitation23.3 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: Pullman 2 Nw, WA (10 mi away); precipitation: Palouse 3.2 Ssw, WA (4 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.

Washington planting zones →

Questions about 99161

What planting zone is ZIP code 99161?

ZIP code 99161 (Palouse, 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 Palouse, WA?

The median last spring frost (32 °F) near 99161 is May 6; after May 25 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Pullman 2 Nw station.

When is the first frost in Palouse, WA?

The median first fall frost near 99161 is September 29, giving a median frost-free growing season of 143 days.

When should I plant tomatoes in 99161?

Start tomato seeds indoors around Mar 11 – Mar 25 and set transplants outside around May 13 – May 27, one to three weeks after the median last frost.

How much rain and snow does 99161 get?

About 23.3 inches of precipitation a year (NOAA 1991–2020 normals, Palouse 3.2 Ssw station).

How hot do summers get in Palouse, WA?

The average high peaks at 85 °F in August, with about 22 days a year at 90 °F or more.

What kind of soil does 99161 have?

The USDA soil survey maps Palouse at the center of ZIP 99161: silt loam, well drained, pH about 6.5 (neutral).

Did spring come early in Palouse, WA in 2026?

Spring leaf-out near 99161 came on Mar 23 in 2026, 15 days earlier than the 1991–2020 average (Apr 7), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Palouse, WA?

Long-day onions: the longest day near 99161 is 15 h 53 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).