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

Planting zone for 99104 — Belmont, WA

ZIP code 99104 (Belmont, Whitman County) is in USDA zone 6b: the coldest winter night averages −5 to 0 °F. The median last spring frost is May 7 and the first fall frost September 28.

Where ZIP 99104 is

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 7
First frostSep 28
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 Belmont, 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 Belmont, WA

JanFebMarAprMayJunJulAugSepOctNovDec
Blue: frost possible · fading green: frost risk falling or rising (90% → 10%) · green: frost-free
Last spring frostMay 7median — 50% chance of a later frost
Safe for tender plantsMay 25only 10% chance of frost after
First fall frostSeptember 28median — 10% chance by Sep 11
Growing season144 daysfrost-free, median

A hard freeze (28 °F) usually ends around April 20 and returns around October 12.

From the NOAA station Rosalia, WA — 14 miles away, elevation 2,421 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 99104

JanFebMarAprMayJunJulAugSepOctNovDec
PeasSow outdoors · Mar 26 – Apr 9
SpinachSow outdoors · Mar 26 – Apr 16
Broccoli, cabbageStart indoors · Feb 26 – Mar 12
Broccoli, cabbageTransplant · Apr 16 – Apr 30
Onion setsPlant outdoors · Apr 9 – Apr 23
PotatoesPlant outdoors · Apr 16 – Apr 30
LettuceSow outdoors · Apr 9 – Apr 23
Carrots, beetsSow outdoors · Apr 16 – Apr 30
TomatoesStart indoors · Mar 12 – Mar 26
TomatoesTransplant · May 14 – May 28
Peppers, eggplantStart indoors · Feb 26 – Mar 12
Peppers, eggplantTransplant · May 21 – Jun 4
BeansSow outdoors · May 14 – May 28
Sweet cornSow outdoors · May 14 – May 28
Cucumbers, squashSow outdoors · May 14 – May 28
Fall lettuce, spinachSow outdoors · Aug 3 – Aug 17
GarlicPlant cloves · Sep 14 – Oct 19
Start seeds indoorsSow or plant outdoorsFall plantingMedian last & first frost

Counted from the median last spring frost (May 7) and first fall frost (Sep 28) 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 99104 came on Mar 23 — 14 days earlier than the 1991–2020 average (Apr 6).

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 Belmont, WA.

Soil in Belmont, WA

The soil mapped at the center of ZIP 99104 is Caldwell — silt loam, somewhat poorly drained.

TextureSilt loama good balance for most vegetables
pH7.0neutral; most vegetables like 6.0–7.0
DrainageSomewhat poorly drainedconsider raised beds
Organic matter6%high
Hydrologic groupCwater soaks in slowly
Farmland classPrime farmland if drainedUSDA classification

Map unit: Caldwell silt loam, drained.

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 99104; soils change within a few hundred feet, so a home soil test (pH, nutrients) is still the best guide.

Climate in Belmont, WA

Summer high86 °Faverage high, August
Winter low24 °Faverage low, December
Hot days25days a year at 90 °F or more
Freezing nights146nights a year at 32 °F or less
Growing degree days2,044base 50 °F — the season’s usable heat
Longest day15 h 54 mindaylight on June 21
Shortest day8 h 30 mindaylight on December 21
Onions to growLong-daysummer days reach 15+ hours, enough for long-day varieties (intermediate types work too)
Precipitation18.4 inper year, rain and melted snow
Snowfall26 inper year

Average high and low, by month

10°20°30°40°50°60°70°80°90°100°32 °FJanuary: average high 37 °F, low 25 °F 37°25° JanFebruary: average high 42 °F, low 26 °F 42°26° FebMarch: average high 50 °F, low 31 °F 50°31° MarApril: average high 58 °F, low 35 °F 58°35° AprMay: average high 67 °F, low 42 °F 67°42° MayJune: average high 73 °F, low 47 °F 73°47° JunJuly: average high 85 °F, low 51 °F 85°51° JulAugust: average high 86 °F, low 51 °F 86°51° AugSeptember: average high 76 °F, low 44 °F 76°44° SepOctober: average high 61 °F, low 35 °F 61°35° OctNovember: average high 45 °F, low 29 °F 45°29° NovDecember: average high 36 °F, low 24 °F 36°24° Dec

Precipitation by month inches · ❄ = snowfall

0″1″2″3″January: 2.03 in precipitation, 6.4 in snowfall 2.0❄6 JanFebruary: 1.72 in precipitation, 3.2 in snowfall 1.7❄3 FebMarch: 1.90 in precipitation, 1.6 in snowfall 1.9❄2 MarApril: 1.55 in precipitation, 0.2 in snowfall 1.6 AprMay: 1.66 in precipitation 1.7 MayJune: 1.33 in precipitation 1.3 JunJuly: 0.52 in precipitation 0.5 JulAugust: 0.42 in precipitation 0.4 AugSeptember: 0.62 in precipitation 0.6 SepOctober: 1.53 in precipitation, 0.1 in snowfall 1.5 OctNovember: 2.46 in precipitation, 3.9 in snowfall 2.5❄4 NovDecember: 2.66 in precipitation, 10.8 in snowfall 2.7❄11 Dec

NOAA NCEI U.S. Climate Normals 1991–2020 — temperature: Rosalia, WA (14 mi away); precipitation: Rosalia, WA (14 mi away). Daylight is calculated from latitude.

Nearby ZIP codes

All 8 nearest ZIP codes share zone 6b.

991286b
Farmington, WA · 5 mi
991586b
Oakesdale, WA · 5 mi
991306b
Garfield, WA · 6 mi
991746b
Steptoe, WA · 10 mi
990336b
Tekoa, WA · 11 mi
991766b
Thornton, WA · 11 mi
838246b
Desmet, ID · 11 mi
991616b
Palouse, WA · 12 mi

Washington planting zones →

Questions about 99104

What planting zone is ZIP code 99104?

ZIP code 99104 (Belmont, 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 Belmont, WA?

The median last spring frost (32 °F) near 99104 is May 7; after May 25 there is only a 10% chance of frost. Data: NOAA 1991–2020 normals, Rosalia station.

When is the first frost in Belmont, WA?

The median first fall frost near 99104 is September 28, giving a median frost-free growing season of 144 days.

When should I plant tomatoes in 99104?

Start tomato seeds indoors around Mar 12 – Mar 26 and set transplants outside around May 14 – May 28, one to three weeks after the median last frost.

How much rain and snow does 99104 get?

About 18.4 inches of precipitation a year and 26 inches of snowfall (NOAA 1991–2020 normals, Rosalia station).

How hot do summers get in Belmont, WA?

The average high peaks at 86 °F in August, with about 25 days a year at 90 °F or more.

What kind of soil does 99104 have?

The USDA soil survey maps Caldwell at the center of ZIP 99104: silt loam, somewhat poorly drained, pH about 7.0 (neutral).

Did spring come early in Belmont, WA in 2026?

Spring leaf-out near 99104 came on Mar 23 in 2026, 14 days earlier than the 1991–2020 average (Apr 6), according to the USA National Phenology Network Spring Index.

What kind of onions grow in Belmont, WA?

Long-day onions: the longest day near 99104 is 15 h 54 min, so summer days reach 15+ hours, enough for long-day varieties (intermediate types work too).