Whitman County, in Washington, sits in USDA hardiness zone 7a — a zone band wide enough that plant choice, not possibility, is the interesting question.
Expect cabbage, pawpaw, california poppy, and collard greens to be strong candidates here; the deciding factors on any one parcel stay local — soil, sun, and drainage.
Whitman County lies within the Palouse and the Columbia Basin — a regional growing area with its own character.
Grounded in USDA PHZM 2023 · Growable Ground suitability scoring · NOAA 1991–2020 Climate Normals
Whitman County holds more than one microclimate.
Soils and elevations shift across Whitman County, so your frost dates and drainage aren't the county average. Enter your address and we'll score 1,086 plants against your land's actual soil, sun, and frost.
We read public map data around Whitman County — soil, climate, flood, and parcel records. How we handle your address.
No card required · your full report in seconds
Whitman County — the short answer
Whitman County, Washington: USDA zone 7a, about 199 days between hard freezes, across 1.4M acres.
- USDA zone
- 7a
- USDA PHZM 2023
- Last hard freeze (28°F)
- Apr 8
- NOAA 1991–2020 Climate Normals, 28°F
- First hard freeze (28°F)
- Oct 24
- NOAA 1991–2020 Climate Normals, 28°F
- Days between freezes
- ~199
- NOAA 1991–2020 Climate Normals, 28°F
- County area
- 1.4M acres
- US Census TIGER/Line 2025
Every figure names the dataset it came from. Hard-freeze dates are county 28°F normals: light frosts run a few weeks past them, and tender transplants usually wait 2–3 weeks after the last hard freeze.
Hardiness Zone Range
Zone 7a is Whitman County's average, not your lot's — a low corner or a tree line moves it. Against Whitman County's 199-day season, see what your own ground reads.
Heat in Whitman County
Across a year, Whitman County accumulates about 1,938 growing degree days above 50°F, about 225 more than the middle Washington county — ahead of 30 of Washington’s 39 counties. Degree days are the heat a crop actually gets to work with — more of them is more room to ripen a long-season crop before the freeze closes the window.
Grounded in PRISM Climate Group, Oregon State University — 1991–2020 monthly normals
Soil in Whitman County
Across Whitman County, the ground is predominantly Mollisols, where Palouse, Athena, and Walla Walla are the most extensive named soil series. The soil is generally well drained with a silt loam surface. Topsoil pH runs about 6.5–7.2, neutral. Rainfall drains through hydrologic group B soils.
Soil order
Mollisols
Drainage
Well drained
Prime farmland
6%
Hydric soils
1%
Soil still varies lot by lot — soil types explained.
How the ground varies across Whitman County
The USDA soil survey maps 86% of Whitman County as well drained — but another 13% drains differently: 7% moderately well drained, 5% somewhat poorly drained.
Palouse is the most extensive named soil at 25% of mapped acres, then Athena (15%) and Walla Walla (15%).
Which of them your own lot sits on is a parcel question, not a county one. Check your address for the survey at your boundary.
What this means for growing in Whitman County
Each reading below is measured for Whitman County itself — here is what it means for a garden here, and the move an experienced grower makes about it.
Drainage
MeasuredThe dominant soils across Whitman County are well drained, in hydrologic group B — ground that drains quickly.
The upside is soil you can work early in spring and roots that never drown; the cost is that fast-draining ground dries out fast and leaches nutrients away before plants can use them.
Work in compost and mulch to hold moisture and feed, and water more often in short doses than deep and rarely.
USDA NRCS SSURGO
Surface pH
MeasuredTopsoil across Whitman County runs about pH 6.5–7.2, close to neutral.
This is the range most vegetables prefer — one correction you probably do not have to make, which is genuinely good news for a new bed.
Keep it there with compost rather than lime or sulfur, and only amend if your own soil test says otherwise.
USDA NRCS SSURGO
Season length
MeasuredWhitman County runs about 199 days between hard freezes — a moderate growing season.
There is room for the full run of cool-season crops plus a warm-season main crop, but the calendar is tight enough that a late spring or early fall frost still decides how much finishes.
Time warm-season transplants to your last hard freeze, and a few weeks of season extension turns a near-miss harvest into a sure one.
NOAA 1991–2020 Climate Normals
Winter hardiness
MeasuredWhitman County sits in USDA hardiness zone 7a.
The zone sets which perennials, shrubs, and fruit trees live through an average winter here — a plant rated for a colder zone is a safe bet, one rated warmer needs winter protection or gets treated as an annual.
Match perennials and fruit to the zone before you buy, so nothing you plant is a gamble against the cold.
USDA PHZM 2023
The kind of country Whitman County is in
Whitman County sits in the Columbia Plateau — EPA Level III, inside the wider North American Deserts. One consistent ecological setting across the whole county.
What Grows in Whitman County
We scored all 1,086 plants against Whitman County's own USDA zone 7a and its own 199-day season between hard freezes, using the same matching engine that runs a full parcel report. These cleared both. Sun, soil pH and drainage vary lot by lot — those are the parcel questions below. Each card opens that plant's Washington profile.
Is it too late to plant in Whitman County?
Rarely: the season closes in stages, not all at once, and each stage has its crops. Cool-season crops can go in from around Mar 11; tender transplants wait until two to three weeks after the last 28°F hard freeze, which lands near Apr 8 (NOAA 1991–2020 climate normals); and from midsummer, planting counts back from the first fall freeze around Oct 24 — long-season crops need about 90 days of runway, quick greens only 30. Even past midsummer there is room for a true fall garden here, and garlic planted near the close carries the momentum into next year.
Documented around Whitman County
- monarch butterfly7 documented records
Sighting records, so they follow observers as much as insects.
What gets applied to farmland in Whitman County
USGS estimates 820,042 lb of Glyphosate on Whitman County farmland in 2019, its largest by weight, ahead of Bromoxynil (117,263 lb) and 2,4-d (75,493 lb).
Farmland across the whole county, not any one lot. Check your address for the site-by-site record.
Safe to Grow Here?
What the federal record shows across Whitman County — and how to grow with it.
We checked the federal record across Whitman County — 496 documented sites across 7 of the 9 source types we track.
The most significant on record: 1 Superfund site (none NPL-listed). Sites tracked in EPA's Superfund program — from assessment-stage CERCLIS entries to confirmed National Priorities List cleanup sites.
There's a meaningful federal record across Whitman County — worth a look before you plant food, not a reason to hold back from growing. Proximity to a documented site is information, not a diagnosis of any one yard. A soil test before new food beds is the sensible precaution here, and the map shows exactly which sites sit where, so you can see what's actually near you.
Sources: EPA, USGS — 1.8M documented sites tracked nationwide across 9 federal source types.
What's on the federal record near Whitman County
Closest first, across Whitman County. Listing isn't leaking, and distance isn't exposure.
- 16N/43E-07K01Nitrate · 4.4 mi
- 17N/42E-14C01 LE10Nitrate · 5.2 mi
- COLFAX WATER DEPARTMENT CITY OFPFAS · 5.3 mi
- 16N/43E-20E01 SU12Nitrate · 5.5 mi
- 16N/43E-20E02 SU011Nitrate · 5.5 mi
- 16N/41E-16K01 LE03Nitrate · 6.2 mi
- S & R GRAIN COMPANYUnderground Storage Tanks · 6.3 mi
- JDK FARMS INCUnderground Storage Tanks · 6.3 mi
- MARVIN L AESCHLIMANUnderground Storage Tanks · 6.3 mi
- CECIL F LARUEUnderground Storage Tanks · 6.3 mi
- FARM SHOPUnderground Storage Tanks · 6.3 mi
- RICHARD MCCULLYUnderground Storage Tanks · 6.3 mi
6 more sites are on the record inside the same radius. See them on the map
Measured from Whitman County's center, not your beds. Run your own address for what's upwind of you specifically.
Environmental Intelligence
The counts behind that headline — every source type on the record near Whitman County.
Total Sites
496
across Whitman County
Risk Level
Elevated
Highest-severity
1 Superfund site (none NPL-listed)
Sources Checked
across Whitman County
Severity Distribution
across Whitman County
Highest-Severity Sites
A note from Gnorman
What an experienced grower watches for around here
In and around Whitman County, two things run higher than the national average across Whitman County — Nitrate (144 sites) and Underground Storage Tanks (307 sites). It's not cause for alarm — it's worth knowing, and there's a sensible way to grow around it.
Nitrate: Nitrate contamination primarily comes from agricultural fertilizer runoff and failing septic systems.
Underground Storage Tanks: Underground storage tanks are the single most common source of soil contamination near homes and gardens.
Test well water for nitrate if you rely on a private well for irrigation (EPA standard: 10 mg/L).
Use raised beds with imported soil — this eliminates the primary soil-contact pathway.
Check your specific parcel in Whitman County
Get exact proximity distances to contamination sources for your specific parcel — plus soil, sun, drainage, and 1,086 plant recommendations.
25+ data sources read at your address, not the Whitman County average
Your land is one point inside Whitman County
Everything above resolves to Whitman County as a whole — one PHZM band and one county frost record, read across 1.4M acres. Your parcel is one point inside that footprint. Slope, tree cover, a low spot that pools cold air, and what is in the soil are all resolved at the address, and none of them are visible at county scale. That is the honest boundary of this page, and the reason the next step is a reading of your own ground rather than a better county average.
Your Lot vs the Whitman County Average
Whitman County Average
- ●USDA Zones 7a, averaged across Whitman County
- ●One soil character for all of Whitman County
- ●Frost dates read at Whitman County's scale: Apr 8 to Oct 24
YOUR Parcel
- ✓Your exact zone, not Whitman County's 7a
- ✓Your SSURGO soil type & pH
- ✓Your sun exposure, cast in 3D
See MY Growing Report
Read your parcel in Whitman County
Pull a site-specific report for your exact address in Whitman County, Washington — soil, sun, drainage, frost risk, and scored plant recommendations.
Three things about your lot that Whitman County averages can't show:
We read public map data around Whitman County — soil, climate, flood, and parcel records. How we handle your address.
25+ data sources read at your address, not the Whitman County average
How we know this about Whitman County
The datasets: hardiness from the USDA ARS Plant Hardiness Zone Map 2023, read at county grain; hard-freeze dates from NOAA 1991–2020 28°F normals at this county’s own record where one resolves, and the labelled statewide window where none does; soils from the USDA NRCS SSURGO survey, area-weighted across the county’s own map units; boundaries and acreage from US Census TIGER/Line 2025; the contamination and pesticide records from the federal sources named in their beats above. Where Whitman County carries no record of its own, the figure is inherited and labelled — the resolution ledger below names each.
Common questions about Whitman County
When does frost risk typically end in Whitman County?
The last hard freeze (28°F) in Whitman County typically lands around Apr 8, per NOAA 1991–2020 climate normals — earlier than the light-frost dates most charts quote. That marks the hard freeze, not the last light frost — lighter frosts keep biting past it, which is why tender transplants here wait until about Apr 29.
How long is the growing season in Whitman County?
Measured between 28°F hard freezes, Whitman County sees about 199 frost-free days — roughly Apr 8 through Oct 24, per NOAA 1991–2020 climate normals. Tender crops work a shorter one: nearer Apr 29 to Oct 10, about 164 days.
Is the soil safe to grow vegetables in Whitman County?
The federal record around Whitman County is a meaningful one — 496 documented sites, mostly Underground Storage Tanks entries (307), the nearest Nitrate record about 4.4 miles out — so a soil test before new food beds is a sensible precaution here, not a reason to hold back from growing. Remember that proximity to a documented site is information, not a diagnosis of any one yard; the contamination map shows exactly what sits where.
Everything above is measured at Whitman County's scale — its 7a band and its 199-day season. Your yard writes its own version of Whitman County's numbers: we read soil, sun, drainage and frost at your exact address. Try it for 14 days — no card required.
Will It Grow Here?
Zone fit is the first question — each answer below reads Washington's frost window, season length, and soil profile against the plant's real requirements.
What this page reads at Whitman County’s own scale
9 of the readings below were taken at Whitman County's own scale — its own ~199-day span between 28°F freezes, the 3 most extensive soil series mapped here and 496 documented sites inside its boundary; one is borrowed from a wider read, named and linked below.
Measured here
- Whitman County's own USDA hardiness band, zones 7aUSDA PHZM 2023
- Whitman County's own 28°F hard-freeze dates and its ~199-day span between themNOAA 1991–2020 Climate Normals
- The soil order, drainage, surface pH, and the 3 most extensive named soil series mapped in Whitman CountyUSDA NRCS SSURGO
- 496 documented contamination sites inside the county boundary, distance-sorted from its center — the closest Nitrate record about 4.4 miles outFederal environmental registers
- Whitman County's boundary and the 1,381,927 acres inside itUS Census TIGER/Line 2025
- Which of 1,086 plants clear zones 7a and a ~199-day seasonGrowable Ground crop-matching engine
- Whitman County sitting wholly inside the Columbia PlateauUS EPA Level III Ecoregions
- Open occurrence records documented in Whitman County for a tracked speciesGBIF derived datasets (CC0 / CC BY 4.0)
- Which agricultural compounds go onto Whitman County farmland, and roughly how muchUSGS NAWQA EPest county estimates
Inherited from a wider read
- The growing challenges every Washington grower plans around — written at state scale, so they stay on the state guidefrom Washington
What this page can’t tell you
- How the season shifts across Whitman County — the ~199 days above is one reading at its centre; the 12 towns below each carry their owntowns in this county →
- The soil pH, drainage, sun hours, and frost pockets on any one lot among Whitman County's 1,381,927 acreswhy one lot differs from the next →
- Which of those 496 documented sites actually reaches your soil — that needs your address, the wind, and the groundwater directionhow we read the record →
- Where cold air settles, which slopes face the sun, and which way the wind runs on your own ground — none of it survives being averaged over Whitman Countyread your own land →