What USDA hardiness zone is Grant County, Washington?

Grant County, Washington spans USDA hardiness zones 6b to 7b. 57% of its ZIP codes are zone 7a, so there is no single zone for the county.

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

The median last spring freeze runs April 21 – May 14 across the 7 NOAA weather stations serving Grant County, Washington, from NOAA 1991-2020 Climate Normals. Half of years freeze later than the median.

Washington

Planting zones in Grant County, Washington

This county spans USDA zones 6b to 7b, so there is no single zone for Grant County and anyone who gives you one is rounding. 57% of its ZIP codes are zone 7a; the rest are not.

USDA zones 6b–7b 3 zones across 14 ZIP codes

ZIP codes 14 14 have a NOAA station within range

Weather stations 7 NOAA 1991–2020 normals, across 2,680 sq mi

Your ZIP code

Get the exact answer for your address

Everything above describes Grant 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 Grant County is closing

Nothing in the 32-crop table still has time to mature here. The first fall freeze normally arrives September 26 – October 21 across the 7 NOAA stations serving this county .

Your next season already has a date

The first job of it is 🧅 Green Onions, start indoors, around February 24 – March 19 — counted back from a last spring freeze of April 21 – May 14 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 7 stations agreeAt least one station

Every one of the 7 NOAA stations serving this county counts May 14 – September 26 as growing season (135 days). Widening to any single station gives April 21 – October 21 (183 days).

That is a 48-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

Grant County covers 3 hardiness zones. A guide that gives the county one zone has picked whichever is largest and rounded everyone else into it — fine for the 57% in zone 7a and wrong for the other 43%. Here is the actual split.

Zone	ZIP codes	Share
7a	8	57%
6b	5	36%
7b	1	7%

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 21 – May 14

First fall freeze September 26 – October 21

Across the 7 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 135–180 days depending which station you are nearest, as published by NOAA rather than computed from the dates above. Summer highs average 82.8–89.4 °F in June–August. Summer rain over the same months runs 0.8–2.0" across those 6 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 11% 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 84 °F summer afternoon drying the soil faster than a cool one.

Every ZIP code in Grant 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
98823	6b	Ephrata Muni AP, WA	9.6 km
98824	7a	Quincy, WA	17.3 km
98832	6b	Odessa, WA	25.0 km
98837	7a	Moses Lake Grant Co AP, WA	6.8 km
98848	7a	Quincy, WA	6.2 km
98851	7a	Ephrata Muni AP, WA	13.4 km
98853	6b	Ephrata Muni AP, WA	24.9 km
98857	7a	Moses Lake Grant Co AP, WA	32.9 km
98860	6b	Hartline, WA	25.0 km
99123	7a	Coulee Dam 1 SW, WA	8.6 km
99135	6b	Hartline, WA	3.3 km
99321	7b	Smyrna, WA	17.7 km
99349	7a	Smyrna, WA	12.1 km
99357	7a	Smyrna, WA	6.1 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 Grant County

Every date below is anchored on the last spring freeze at each station and reported as a range across all 7 of them, because no one station speaks for the county.

Crop	Job	When	Offset
🧅 Green Onions	Start indoors	February 24 – March 19	8 wk before
🌶️ Peppers	Start indoors	February 24 – March 19	8 wk before
🥦 Broccoli	Start indoors	March 10 – April 2	6 wk before
🥬 Cabbage	Start indoors	March 10 – April 2	6 wk before
🥬 Collards	Start indoors	March 10 – April 2	6 wk before
🥬 Kale	Start indoors	March 10 – April 2	6 wk before
🥬 Leaf Lettuce	Start indoors	March 10 – April 2	6 wk before
🫛 Peas	Direct sow	March 10 – April 2	6 wk before
🥬 Spinach	Direct sow	March 10 – April 2	6 wk before
🍠 Sweet Potato	Start indoors	March 10 – April 2	6 wk before
🍅 Tomatoes	Start indoors	March 10 – April 2	6 wk before
🥬 Bok Choy	Start indoors	March 17 – April 9	5 wk before
🥬 Kohlrabi	Start indoors	March 17 – April 9	5 wk before
🥬 Swiss Chard	Start indoors	March 17 – April 9	5 wk before
🥬 Arugula	Direct sow	March 24 – April 16	4 wk before
🥬 Baby Salad Greens	Direct sow	March 24 – April 16	4 wk before
🥕 Beets	Direct sow	March 24 – April 16	4 wk before
🧅 Green Onions	Direct sow	March 24 – April 16	4 wk before
🥬 Mustard Greens	Direct sow	March 24 – April 16	4 wk before
🌶️ Okra	Start indoors	March 24 – April 16	4 wk before
🌱 Radishes	Direct sow	March 24 – April 16	4 wk before
🥔 Turnips	Direct sow	March 24 – April 16	4 wk before
🥬 Cabbage	Set out	March 31 – April 23	3 wk before
🥕 Carrots	Direct sow	March 31 – April 23	3 wk before
🥬 Collards	Direct sow	March 31 – April 23	3 wk before
🥬 Collards	Set out	March 31 – April 23	3 wk before
🥒 Cucumbers	Start indoors	March 31 – April 23	3 wk before
🧅 Green Onions	Set out	March 31 – April 23	3 wk before
🥬 Kale	Direct sow	March 31 – April 23	3 wk before
🥬 Kale	Set out	March 31 – April 23	3 wk before
🥬 Kohlrabi	Direct sow	March 31 – April 23	3 wk before
🥬 Kohlrabi	Set out	March 31 – April 23	3 wk before
🥬 Leaf Lettuce	Direct sow	March 31 – April 23	3 wk before
🎃 Pumpkins	Start indoors	March 31 – April 23	3 wk before
🎃 Summer Squash	Start indoors	March 31 – April 23	3 wk before
🎃 Winter Squash	Start indoors	March 31 – April 23	3 wk before
🥒 Zucchini	Start indoors	March 31 – April 23	3 wk before
🥬 Bok Choy	Direct sow	April 7 – April 30	2 wk before
🥬 Bok Choy	Set out	April 7 – April 30	2 wk before
🥦 Broccoli	Set out	April 7 – April 30	2 wk before
🌿 Cilantro	Direct sow	April 7 – April 30	2 wk before
🥬 Leaf Lettuce	Set out	April 7 – April 30	2 wk before
🥬 Swiss Chard	Direct sow	April 7 – April 30	2 wk before
🥬 Swiss Chard	Set out	April 7 – April 30	2 wk before
🌿 Dill	Direct sow	April 14 – May 7	1 wk before
🫘 Bush Beans	Direct sow	April 28 – May 21	1 wk after
🥒 Cucumbers	Set out	April 28 – May 21	1 wk after
🎃 Pumpkins	Direct sow	April 28 – May 21	1 wk after
🎃 Pumpkins	Set out	April 28 – May 21	1 wk after
🎃 Summer Squash	Direct sow	April 28 – May 21	1 wk after
🎃 Summer Squash	Set out	April 28 – May 21	1 wk after
🌽 Sweet Corn	Direct sow	April 28 – May 21	1 wk after
🍅 Tomatoes	Set out	April 28 – May 21	1 wk after
🎃 Winter Squash	Direct sow	April 28 – May 21	1 wk after
🎃 Winter Squash	Set out	April 28 – May 21	1 wk after
🥒 Zucchini	Direct sow	April 28 – May 21	1 wk after
🥒 Zucchini	Set out	April 28 – May 21	1 wk after
🥒 Cucumbers	Direct sow	May 5 – May 28	2 wk after
🌶️ Okra	Direct sow	May 5 – May 28	2 wk after
🌶️ Okra	Set out	May 5 – May 28	2 wk after
🌶️ Peppers	Set out	May 5 – May 28	2 wk after
🫘 Southern Peas	Direct sow	May 5 – May 28	2 wk after
🍠 Sweet Potato	Set out	May 5 – May 28	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 Grant 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 May 31 to be careful. Median April 21 – May 14 across 7 stations; April 3 is the optimistic end.
First fall freeze: Plan to September 10 to be careful. Median September 26 – October 21 across 7 stations; November 5 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 7 stations behind these numbers

All 7 NOAA stations whose normals this page quotes, spanning about 124 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
Coulee Dam 1 SW, WA	USC00451767	April 22	October 21	180 days
Ephrata Muni AP, WA	USW00024141	April 22	October 17	175 days
Hartline, WA	USC00453529	May 2	October 12	162 days
Moses Lake Grant Co AP, WA	USW00024110	April 27	October 8	165 days
Odessa, WA	USC00456039	May 14	September 26	135 days
Quincy, WA	USC00456880	April 21	October 16	178 days
Smyrna, WA	USC00457727	April 23	October 12	172 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

Grant 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–7b

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.