What USDA hardiness zone is Sweetwater County, Wyoming?

Sweetwater County, Wyoming spans USDA hardiness zones 4a to 5b. 45% of its ZIP codes are zone 5a, so there is no single zone for the county.

When is the last spring frost in Sweetwater County, Wyoming?

The median last spring freeze runs May 21 – June 5 across the 8 NOAA weather stations serving Sweetwater County, Wyoming, from NOAA 1991-2020 Climate Normals. Half of years freeze later than the median.

Wyoming

Planting zones in Sweetwater County, Wyoming

This county spans USDA zones 4a to 5b, so there is no single zone for Sweetwater County and anyone who gives you one is rounding. 45% of its ZIP codes are zone 5a; the rest are not.

USDA zones 4a–5b 4 zones across 11 ZIP codes

ZIP codes 11 11 have a NOAA station within range

Weather stations 8 NOAA 1991–2020 normals, across 10,427 sq mi

Your ZIP code

Get the exact answer for your address

Everything above describes Sweetwater County, Wyoming 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 Sweetwater County is closing

Nothing in the 32-crop table still has time to mature here. The first fall freeze normally arrives September 14 – September 29 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 March 26 – April 10 — counted back from a last spring freeze of May 21 – June 5 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 June 5 – September 14 as growing season (101 days). Widening to any single station gives May 21 – September 29 (131 days).

That is a 30-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

Sweetwater County covers 4 hardiness zones. A guide that gives the county one zone has picked whichever is largest and rounded everyone else into it — fine for the 45% in zone 5a and wrong for the other 55%. Here is the actual split.

Zone	ZIP codes	Share
5a	5	45%
5b	3	27%
4b	2	18%
4a	1	9%

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 May 21 – June 5

First fall freeze September 14 – September 29

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 101–128 days depending which station you are nearest, as published by NOAA rather than computed from the dates above. Summer highs average 79.7–83.3 °F in June–August. Summer rain over the same months runs 1.7–3.6" across those 7 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 16% 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 82 °F summer afternoon drying the soil faster than a cool one.

Every ZIP code in Sweetwater 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
82322	5b	Muddy Gap, WY	15.5 km
82336	4b	Wamsutter, WY	19.3 km
82901	5b	Rock Springs AP, WY	24.7 km
82929	5a	Church Buttes Gas Plt, WY	23.9 km
82932	4a	Rock Springs Fire Dept, WY	62.0 km
82934	4b	Church Buttes Gas Plt, WY	25.1 km
82935	5a	Green Rvr, WY	23.9 km
82938	5b	Manila, UT	18.5 km
82942	5a	Bitter Creek 4 NE, WY	24.5 km
82943	5a	Rock Springs Fire Dept, WY	14.6 km
82945	5a	Rock Springs AP, WY	16.9 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 Sweetwater 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	March 26 – April 10	8 wk before
🌶️ Peppers	Start indoors	March 26 – April 10	8 wk before
🥦 Broccoli	Start indoors	April 9 – April 24	6 wk before
🥬 Cabbage	Start indoors	April 9 – April 24	6 wk before
🥬 Collards	Start indoors	April 9 – April 24	6 wk before
🥬 Kale	Start indoors	April 9 – April 24	6 wk before
🥬 Leaf Lettuce	Start indoors	April 9 – April 24	6 wk before
🫛 Peas	Direct sow	April 9 – April 24	6 wk before
🥬 Spinach	Direct sow	April 9 – April 24	6 wk before
🍠 Sweet Potato	Start indoors	April 9 – April 24	6 wk before
🍅 Tomatoes	Start indoors	April 9 – April 24	6 wk before
🥬 Bok Choy	Start indoors	April 16 – May 1	5 wk before
🥬 Kohlrabi	Start indoors	April 16 – May 1	5 wk before
🥬 Swiss Chard	Start indoors	April 16 – May 1	5 wk before
🥬 Arugula	Direct sow	April 23 – May 8	4 wk before
🥬 Baby Salad Greens	Direct sow	April 23 – May 8	4 wk before
🥕 Beets	Direct sow	April 23 – May 8	4 wk before
🧅 Green Onions	Direct sow	April 23 – May 8	4 wk before
🥬 Mustard Greens	Direct sow	April 23 – May 8	4 wk before
🌶️ Okra	Start indoors	April 23 – May 8	4 wk before
🌱 Radishes	Direct sow	April 23 – May 8	4 wk before
🥔 Turnips	Direct sow	April 23 – May 8	4 wk before
🥬 Cabbage	Set out	April 30 – May 15	3 wk before
🥕 Carrots	Direct sow	April 30 – May 15	3 wk before
🥬 Collards	Direct sow	April 30 – May 15	3 wk before
🥬 Collards	Set out	April 30 – May 15	3 wk before
🥒 Cucumbers	Start indoors	April 30 – May 15	3 wk before
🧅 Green Onions	Set out	April 30 – May 15	3 wk before
🥬 Kale	Direct sow	April 30 – May 15	3 wk before
🥬 Kale	Set out	April 30 – May 15	3 wk before
🥬 Kohlrabi	Direct sow	April 30 – May 15	3 wk before
🥬 Kohlrabi	Set out	April 30 – May 15	3 wk before
🥬 Leaf Lettuce	Direct sow	April 30 – May 15	3 wk before
🎃 Pumpkins	Start indoors	April 30 – May 15	3 wk before
🎃 Summer Squash	Start indoors	April 30 – May 15	3 wk before
🎃 Winter Squash	Start indoors	April 30 – May 15	3 wk before
🥒 Zucchini	Start indoors	April 30 – May 15	3 wk before
🥬 Bok Choy	Direct sow	May 7 – May 22	2 wk before
🥬 Bok Choy	Set out	May 7 – May 22	2 wk before
🥦 Broccoli	Set out	May 7 – May 22	2 wk before
🌿 Cilantro	Direct sow	May 7 – May 22	2 wk before
🥬 Leaf Lettuce	Set out	May 7 – May 22	2 wk before
🥬 Swiss Chard	Direct sow	May 7 – May 22	2 wk before
🥬 Swiss Chard	Set out	May 7 – May 22	2 wk before
🌿 Dill	Direct sow	May 14 – May 29	1 wk before
🫘 Bush Beans	Direct sow	May 28 – June 12	1 wk after
🥒 Cucumbers	Set out	May 28 – June 12	1 wk after
🎃 Pumpkins	Direct sow	May 28 – June 12	1 wk after
🎃 Pumpkins	Set out	May 28 – June 12	1 wk after
🎃 Summer Squash	Direct sow	May 28 – June 12	1 wk after
🎃 Summer Squash	Set out	May 28 – June 12	1 wk after
🌽 Sweet Corn	Direct sow	May 28 – June 12	1 wk after
🍅 Tomatoes	Set out	May 28 – June 12	1 wk after
🎃 Winter Squash	Direct sow	May 28 – June 12	1 wk after
🎃 Winter Squash	Set out	May 28 – June 12	1 wk after
🥒 Zucchini	Direct sow	May 28 – June 12	1 wk after
🥒 Zucchini	Set out	May 28 – June 12	1 wk after
🥒 Cucumbers	Direct sow	June 4 – June 19	2 wk after
🌶️ Okra	Direct sow	June 4 – June 19	2 wk after
🌶️ Okra	Set out	June 4 – June 19	2 wk after
🌶️ Peppers	Set out	June 4 – June 19	2 wk after
🫘 Southern Peas	Direct sow	June 4 – June 19	2 wk after
🍠 Sweet Potato	Set out	June 4 – June 19	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 Sweetwater County

Zone 5a carries 48 of 74 perennial edibles; zone 4a carries 34. 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 23 to be careful. Median May 21 – June 5 across 8 stations; May 4 is the optimistic end.
First fall freeze: Plan to September 1 to be careful. Median September 14 – September 29 across 8 stations; October 14 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 152 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
Bitter Creek 4 NE, WY	USC00480761	June 1	September 16	106 days
Church Buttes Gas Plt, WY	USC00481736	May 25	September 27	124 days
Green Rvr, WY	USC00484065	May 24	September 22	120 days
Manila, UT	USC00425377	May 22	September 29	128 days
Muddy Gap, WY	USC00486595	May 21	September 27	126 days
Rock Springs AP, WY	USW00024027	May 22	September 28	126 days
Rock Springs Fire Dept, WY	USC00487847	May 24	September 24	121 days
Wamsutter, WY	USC00489459	June 5	September 14	101 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

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

More of Wyoming

Counties with the same zones — 4a–5b

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.

Trunk wrapZone 4a is cold enough that winter sun on a young trunk does more damage than the cold does.
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 4a, 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.