What USDA hardiness zone is Whitman County, Washington?

Whitman County, Washington spans USDA hardiness zones 6b to 7a. 60% of its ZIP codes are zone 6b, so there is no single zone for the county.

When is the last spring frost in Whitman County, Washington?

The median last spring freeze runs April 6 – May 15 across the 8 NOAA weather stations serving Whitman County, Washington, from NOAA 1991-2020 Climate Normals. Half of years freeze later than the median.

Washington

Planting zones in Whitman County, Washington

This county spans USDA zones 6b to 7a, so there is no single zone for Whitman County and anyone who gives you one is rounding. 60% of its ZIP codes are zone 6b; the rest are not.

USDA zones 6b–7a 2 zones across 20 ZIP codes

ZIP codes 20 20 have a NOAA station within range

Weather stations 8 NOAA 1991–2020 normals, across 2,159 sq mi

Your ZIP code

Get the exact answer for your address

Everything above describes Whitman County, Washington as a whole. Hardiness zones and freeze dates are published per ZIP code, so yours is exact — enter it and this page will tell you your zone, which NOAA station it comes from and how far away that station is.

The growing season in Whitman County is closing

Nothing in the 32-crop table still has time to mature here. The first fall freeze normally arrives September 21 – October 26 across the 8 NOAA stations serving this county .

Your next season already has a date

The first job of it is 🧅 Green Onions, start indoors, around February 9 – March 20 — counted back from a last spring freeze of April 6 – May 15 here.

Every spring date for your ZIP →

These are ranges across the whole county. The ZIP lookup above gives the dates from your own nearest station instead.

All 8 stations agreeAt least one station

Every one of the 8 NOAA stations serving this county counts May 15 – September 21 as growing season (129 days). Widening to any single station gives April 6 – October 26 (203 days).

That is a 74-day difference inside one county — which is why this page gives ranges rather than a single planting date. The ZIP lookup above resolves it to one station.

Which zone you are in depends where you are

Whitman County covers 2 hardiness zones. A guide that gives the county one zone has picked whichever is largest and rounded everyone else into it — fine for the 60% in zone 6b and wrong for the other 40%. Here is the actual split.

Zone	ZIP codes	Share
6b	12	60%
7a	8	40%

Zones are published per ZIP code, so yours is exact even though the county's is not. The hardiness tool will tell you which one you are in.

Your freeze dates

Last spring freeze April 6 – May 15

First fall freeze September 21 – October 26

Across the 8 NOAA stations serving this county. These are medians — half of years freeze later than the date shown — so treat the later end of each range as the cautious one.

The growing season runs 126–200 days depending which station you are nearest, as published by NOAA rather than computed from the dates above. Summer highs average 78–86.6 °F in June–August. Summer rain over the same months runs 1.6–3.4" across those 8 stations, against the rough inch a week — about 13 inches over the same 92 days — that a vegetable garden is usually reckoned to want. The middle station covers about 17% of it, so a summer garden here is watered rather than rained on. The inches are NOAA's published normals; the inch a week is a rule of thumb, and it takes no account of a 81 °F summer afternoon drying the soil faster than a cool one.

Every ZIP code in Whitman County

Zones are published per ZIP code, not per county, so this is the exact answer rather than the county's average. The station column is the nearest one to that ZIP code's centroid and how far away it is — the same figure the tools use, shown here so you can see which ZIP codes are well covered and which are reaching.

ZIP code	USDA zone	Nearest NOAA station	Distance
99017	6b	St John, WA	24.8 km
99033	6b	Plummer 3 Wsw, ID	14.0 km
99102	7a	Pullman 2 NW, WA	6.0 km
99111	7a	Pullman 2 NW, WA	22.8 km
99113	7a	Pullman Moscow Rgnl AP, WA	18.9 km
99125	7a	St John, WA	19.0 km
99128	6b	Potlatch 3 Nne, ID	23.0 km
99130	6b	Potlatch 3 Nne, ID	25.4 km
99136	7a	Lacrosse, WA	16.6 km
99143	7a	Lacrosse, WA	6.3 km
99149	6b	Rosalia, WA	8.0 km
99158	6b	Rosalia, WA	14.7 km
99161	6b	Pullman 2 NW, WA	16.2 km
99163	6b	Pullman 2 NW, WA	4.1 km
99170	6b	Rosalia, WA	3.2 km
99171	6b	St John, WA	5.0 km
99174	6b	St John, WA	19.9 km
99176	6b	St John, WA	13.3 km
99179	7a	Lewiston Nez Perce Co AP, ID	15.8 km
99333	7a	Lacrosse, WA	23.6 km

ZIP-code positions are area centroids, so a large rural ZIP code's listed distance is measured from the middle of its area rather than from any particular address in it.

When to start seeds in Whitman County

Every date below is anchored on the last spring freeze at each station and reported as a range across all 8 of them, because no one station speaks for the county.

Crop	Job	When	Offset
🧅 Green Onions	Start indoors	February 9 – March 20	8 wk before
🌶️ Peppers	Start indoors	February 9 – March 20	8 wk before
🥦 Broccoli	Start indoors	February 23 – April 3	6 wk before
🥬 Cabbage	Start indoors	February 23 – April 3	6 wk before
🥬 Collards	Start indoors	February 23 – April 3	6 wk before
🥬 Kale	Start indoors	February 23 – April 3	6 wk before
🥬 Leaf Lettuce	Start indoors	February 23 – April 3	6 wk before
🫛 Peas	Direct sow	February 23 – April 3	6 wk before
🥬 Spinach	Direct sow	February 23 – April 3	6 wk before
🍠 Sweet Potato	Start indoors	February 23 – April 3	6 wk before
🍅 Tomatoes	Start indoors	February 23 – April 3	6 wk before
🥬 Bok Choy	Start indoors	March 2 – April 10	5 wk before
🥬 Kohlrabi	Start indoors	March 2 – April 10	5 wk before
🥬 Swiss Chard	Start indoors	March 2 – April 10	5 wk before
🥬 Arugula	Direct sow	March 9 – April 17	4 wk before
🥬 Baby Salad Greens	Direct sow	March 9 – April 17	4 wk before
🥕 Beets	Direct sow	March 9 – April 17	4 wk before
🧅 Green Onions	Direct sow	March 9 – April 17	4 wk before
🥬 Mustard Greens	Direct sow	March 9 – April 17	4 wk before
🌶️ Okra	Start indoors	March 9 – April 17	4 wk before
🌱 Radishes	Direct sow	March 9 – April 17	4 wk before
🥔 Turnips	Direct sow	March 9 – April 17	4 wk before
🥬 Cabbage	Set out	March 16 – April 24	3 wk before
🥕 Carrots	Direct sow	March 16 – April 24	3 wk before
🥬 Collards	Direct sow	March 16 – April 24	3 wk before
🥬 Collards	Set out	March 16 – April 24	3 wk before
🥒 Cucumbers	Start indoors	March 16 – April 24	3 wk before
🧅 Green Onions	Set out	March 16 – April 24	3 wk before
🥬 Kale	Direct sow	March 16 – April 24	3 wk before
🥬 Kale	Set out	March 16 – April 24	3 wk before
🥬 Kohlrabi	Direct sow	March 16 – April 24	3 wk before
🥬 Kohlrabi	Set out	March 16 – April 24	3 wk before
🥬 Leaf Lettuce	Direct sow	March 16 – April 24	3 wk before
🎃 Pumpkins	Start indoors	March 16 – April 24	3 wk before
🎃 Summer Squash	Start indoors	March 16 – April 24	3 wk before
🎃 Winter Squash	Start indoors	March 16 – April 24	3 wk before
🥒 Zucchini	Start indoors	March 16 – April 24	3 wk before
🥬 Bok Choy	Direct sow	March 23 – May 1	2 wk before
🥬 Bok Choy	Set out	March 23 – May 1	2 wk before
🥦 Broccoli	Set out	March 23 – May 1	2 wk before
🌿 Cilantro	Direct sow	March 23 – May 1	2 wk before
🥬 Leaf Lettuce	Set out	March 23 – May 1	2 wk before
🥬 Swiss Chard	Direct sow	March 23 – May 1	2 wk before
🥬 Swiss Chard	Set out	March 23 – May 1	2 wk before
🌿 Dill	Direct sow	March 30 – May 8	1 wk before
🫘 Bush Beans	Direct sow	April 13 – May 22	1 wk after
🥒 Cucumbers	Set out	April 13 – May 22	1 wk after
🎃 Pumpkins	Direct sow	April 13 – May 22	1 wk after
🎃 Pumpkins	Set out	April 13 – May 22	1 wk after
🎃 Summer Squash	Direct sow	April 13 – May 22	1 wk after
🎃 Summer Squash	Set out	April 13 – May 22	1 wk after
🌽 Sweet Corn	Direct sow	April 13 – May 22	1 wk after
🍅 Tomatoes	Set out	April 13 – May 22	1 wk after
🎃 Winter Squash	Direct sow	April 13 – May 22	1 wk after
🎃 Winter Squash	Set out	April 13 – May 22	1 wk after
🥒 Zucchini	Direct sow	April 13 – May 22	1 wk after
🥒 Zucchini	Set out	April 13 – May 22	1 wk after
🥒 Cucumbers	Direct sow	April 20 – May 29	2 wk after
🌶️ Okra	Direct sow	April 20 – May 29	2 wk after
🌶️ Okra	Set out	April 20 – May 29	2 wk after
🌶️ Peppers	Set out	April 20 – May 29	2 wk after
🫘 Southern Peas	Direct sow	April 20 – May 29	2 wk after
🍠 Sweet Potato	Set out	April 20 – May 29	2 wk after

Offsets are published guidance; the dates they land on are computed from measured NOAA normals. The seed-starting tool does this for your own ZIP code and counts the days.

What survives the winter changes across Whitman County

Zone 7a carries 58 of 74 perennial edibles; zone 6b carries 51. The best number is not always the warmest zone — the count peaks in the middle and falls both ways, because the warm end loses plants to insufficient winter chill and summer heat, not to cold.

Hardiness ranges are a judgement, published by growers rather than measured; the zone they are compared against is measured. On a warm-end verdict, check with your local extension service — a coastal zone 8 and an inland zone 8 are not the same summer.

Cautious — shortens the seasonMedian across stationsOptimistic

Last spring freeze: Plan to June 4 to be careful. Median April 6 – May 15 across 8 stations; March 20 is the optimistic end.
First fall freeze: Plan to August 31 to be careful. Median September 21 – October 26 across 8 stations; November 12 is the optimistic end.

NOAA publishes these as probabilities, not averages — the middle figure is a median, so half of years fall either side of it. The cautious end is the 10% tail: in roughly nine years in ten the freeze falls on the safe side of it.

The 8 stations behind these numbers

All 8 NOAA stations whose normals this page quotes, spanning about 104 km north to south. Every one is named with its identifier in the station list below — this page does not single one out, because no one station speaks for a whole county.

A relative sketch, not a map with a projection: longitude is adjusted for latitude so the shape is not stretched, and there is no basemap. For the one station nearest a specific address, with its real distance, use the ZIP lookup above.

These are the stations this county's ZIP codes actually cite as nearest — not a claim that each one sits inside its boundary, since a rural ZIP legitimately reaches over it. Every figure above comes from them, and each is named so you can check it.

Station	NOAA ID	Last spring freeze	First fall freeze	Season
Lacrosse, WA	USC00454338	May 13	September 26	133 days
Lewiston Nez Perce Co AP, ID	USW00024149	April 6	October 26	200 days
Plummer 3 Wsw, ID	USC00107188	May 11	October 5	143 days
Potlatch 3 Nne, ID	USC00107301	May 15	September 21	126 days
Pullman 2 NW, WA	USC00456789	May 6	September 29	143 days
Pullman Moscow Rgnl AP, WA	USW00094129	April 29	October 2	159 days
Rosalia, WA	USC00457180	May 7	September 28	144 days
St John, WA	USC00457267	April 29	October 4	161 days

These are medians, not averages — NOAA publishes freeze dates as a probability distribution, and half of years freeze later than the date shown.

Your own ZIP

Work out your own dates

This page describes a whole county. Every tool below answers for one ZIP code, which is the grain the underlying data is published at.

Other places to compare

Whitman County sits in Washington. That page carries the whole state's zone spread, its metro areas, and every other county in it with a page here.

More of Washington

Counties with the same zones — 6b–7a

Matched on the exact zone set, not a dominant zone, so the winter answer on these pages really is the same one as here.

Gear

If you want to act on this

Each link opens an Amazon search rather than a product we picked. We have not tested these and do not rank them — the search is the honest version, and you choose.

Row cover and frost clothThe season here closes at the first fall freeze dated above — a cover buys back some of those days at the end.
MulchFor the perennials nearest their cold limit in zone 6b, where an insulated crown is what decides whether they come back.

As an Amazon Associate we earn from qualifying purchases. That costs you nothing extra, and it buys no influence over anything on this site: the dates come from NOAA normals and the zones from the USDA, and no product affects either.

Sources

Where these numbers come from

Hardiness zones are the USDA 2023 Plant Hardiness Zone Map, published per ZIP code by PRISM at Oregon State. Freeze dates and growing-season lengths are NOAA 1991–2020 Climate Normals, taken per station and cited above by name and NOAA ID.

County boundaries come from the Census ZCTA-to-county relation, which is what places each ZIP code — and which treats parishes, boroughs and census areas as county equivalents. No station is chosen to represent this county: every range above is taken across all of them and the count is stated, because picking one would be a judgement dressed as a measurement.