What USDA hardiness zone is Big Horn County, Wyoming?

Big Horn County, Wyoming spans USDA hardiness zones 4b to 5a. 69% of its ZIP codes are zone 5a, so there is no single zone for the county.

When is the last spring frost in Big Horn County, Wyoming?

The median last spring freeze runs April 28 – May 16 across the 6 NOAA weather stations serving Big Horn County, Wyoming, from NOAA 1991-2020 Climate Normals. Half of years freeze later than the median.

Wyoming

Planting zones in Big Horn County, Wyoming

This county spans USDA zones 4b to 5a, so there is no single zone for Big Horn County and anyone who gives you one is rounding. 69% of its ZIP codes are zone 5a; the rest are not.

USDA zones 4b–5a 2 zones across 13 ZIP codes

ZIP codes 13 13 have a NOAA station within range

Weather stations 6 NOAA 1991–2020 normals, across 3,137 sq mi

Your ZIP code

Get the exact answer for your address

Everything above describes Big Horn 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 Big Horn County is closing

Nothing in the 32-crop table still has time to mature here. The first fall freeze normally arrives September 23 – October 10 across the 6 NOAA stations serving this county .

Your next season already has a date

The first job of it is 🧅 Green Onions, start indoors, around March 3 – March 21 — counted back from a last spring freeze of April 28 – May 16 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 6 stations agreeAt least one station

Every one of the 6 NOAA stations serving this county counts May 16 – September 23 as growing season (130 days). Widening to any single station gives April 28 – October 10 (165 days).

That is a 35-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

Big Horn 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 69% in zone 5a and wrong for the other 31%. Here is the actual split.

Zone	ZIP codes	Share
5a	9	69%
4b	4	31%

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 28 – May 16

First fall freeze September 23 – October 10

Across the 6 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 130–164 days depending which station you are nearest, as published by NOAA rather than computed from the dates above. Summer highs average 82.5–89.1 °F in June–August. Summer rain over the same months runs 1.8–2.5" 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 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 86 °F summer afternoon drying the soil faster than a cool one.

Every ZIP code in Big Horn 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
82410	4b	Basin, WY	10.1 km
82411	5a	Emblem, WY	8.6 km
82412	5a	Deaver, WY	11.7 km
82420	5a	Lovell, WY	10.2 km
82421	5a	Deaver, WY	0.9 km
82422	5a	Emblem, WY	0.9 km
82423	5a	Deaver, WY	10.6 km
82426	4b	Greybull, WY	3.3 km
82428	5a	Shell, WY	30.2 km
82431	5a	Lovell, WY	19.8 km
82432	4b	Basin, WY	23.6 km
82434	4b	Emblem, WY	18.5 km
82441	5a	Shell, WY	13.3 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 Big Horn County

Every date below is anchored on the last spring freeze at each station and reported as a range across all 6 of them, because no one station speaks for the county.

Crop	Job	When	Offset
🧅 Green Onions	Start indoors	March 3 – March 21	8 wk before
🌶️ Peppers	Start indoors	March 3 – March 21	8 wk before
🥦 Broccoli	Start indoors	March 17 – April 4	6 wk before
🥬 Cabbage	Start indoors	March 17 – April 4	6 wk before
🥬 Collards	Start indoors	March 17 – April 4	6 wk before
🥬 Kale	Start indoors	March 17 – April 4	6 wk before
🥬 Leaf Lettuce	Start indoors	March 17 – April 4	6 wk before
🫛 Peas	Direct sow	March 17 – April 4	6 wk before
🥬 Spinach	Direct sow	March 17 – April 4	6 wk before
🍠 Sweet Potato	Start indoors	March 17 – April 4	6 wk before
🍅 Tomatoes	Start indoors	March 17 – April 4	6 wk before
🥬 Bok Choy	Start indoors	March 24 – April 11	5 wk before
🥬 Kohlrabi	Start indoors	March 24 – April 11	5 wk before
🥬 Swiss Chard	Start indoors	March 24 – April 11	5 wk before
🥬 Arugula	Direct sow	March 31 – April 18	4 wk before
🥬 Baby Salad Greens	Direct sow	March 31 – April 18	4 wk before
🥕 Beets	Direct sow	March 31 – April 18	4 wk before
🧅 Green Onions	Direct sow	March 31 – April 18	4 wk before
🥬 Mustard Greens	Direct sow	March 31 – April 18	4 wk before
🌶️ Okra	Start indoors	March 31 – April 18	4 wk before
🌱 Radishes	Direct sow	March 31 – April 18	4 wk before
🥔 Turnips	Direct sow	March 31 – April 18	4 wk before
🥬 Cabbage	Set out	April 7 – April 25	3 wk before
🥕 Carrots	Direct sow	April 7 – April 25	3 wk before
🥬 Collards	Direct sow	April 7 – April 25	3 wk before
🥬 Collards	Set out	April 7 – April 25	3 wk before
🥒 Cucumbers	Start indoors	April 7 – April 25	3 wk before
🧅 Green Onions	Set out	April 7 – April 25	3 wk before
🥬 Kale	Direct sow	April 7 – April 25	3 wk before
🥬 Kale	Set out	April 7 – April 25	3 wk before
🥬 Kohlrabi	Direct sow	April 7 – April 25	3 wk before
🥬 Kohlrabi	Set out	April 7 – April 25	3 wk before
🥬 Leaf Lettuce	Direct sow	April 7 – April 25	3 wk before
🎃 Pumpkins	Start indoors	April 7 – April 25	3 wk before
🎃 Summer Squash	Start indoors	April 7 – April 25	3 wk before
🎃 Winter Squash	Start indoors	April 7 – April 25	3 wk before
🥒 Zucchini	Start indoors	April 7 – April 25	3 wk before
🥬 Bok Choy	Direct sow	April 14 – May 2	2 wk before
🥬 Bok Choy	Set out	April 14 – May 2	2 wk before
🥦 Broccoli	Set out	April 14 – May 2	2 wk before
🌿 Cilantro	Direct sow	April 14 – May 2	2 wk before
🥬 Leaf Lettuce	Set out	April 14 – May 2	2 wk before
🥬 Swiss Chard	Direct sow	April 14 – May 2	2 wk before
🥬 Swiss Chard	Set out	April 14 – May 2	2 wk before
🌿 Dill	Direct sow	April 21 – May 9	1 wk before
🫘 Bush Beans	Direct sow	May 5 – May 23	1 wk after
🥒 Cucumbers	Set out	May 5 – May 23	1 wk after
🎃 Pumpkins	Direct sow	May 5 – May 23	1 wk after
🎃 Pumpkins	Set out	May 5 – May 23	1 wk after
🎃 Summer Squash	Direct sow	May 5 – May 23	1 wk after
🎃 Summer Squash	Set out	May 5 – May 23	1 wk after
🌽 Sweet Corn	Direct sow	May 5 – May 23	1 wk after
🍅 Tomatoes	Set out	May 5 – May 23	1 wk after
🎃 Winter Squash	Direct sow	May 5 – May 23	1 wk after
🎃 Winter Squash	Set out	May 5 – May 23	1 wk after
🥒 Zucchini	Direct sow	May 5 – May 23	1 wk after
🥒 Zucchini	Set out	May 5 – May 23	1 wk after
🥒 Cucumbers	Direct sow	May 12 – May 30	2 wk after
🌶️ Okra	Direct sow	May 12 – May 30	2 wk after
🌶️ Okra	Set out	May 12 – May 30	2 wk after
🌶️ Peppers	Set out	May 12 – May 30	2 wk after
🫘 Southern Peas	Direct sow	May 12 – May 30	2 wk after
🍠 Sweet Potato	Set out	May 12 – May 30	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 Big Horn County

Zone 5a carries 48 of 74 perennial edibles; zone 4b 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 3 to be careful. Median April 28 – May 16 across 6 stations; April 15 is the optimistic end.
First fall freeze: Plan to September 10 to be careful. Median September 23 – October 10 across 6 stations; October 22 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 6 stations behind these numbers

All 6 NOAA stations whose normals this page quotes, spanning about 57 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
Basin, WY	USC00480540	April 28	October 10	164 days
Deaver, WY	USC00482415	May 6	October 1	148 days
Emblem, WY	USC00483031	May 12	September 28	136 days
Greybull, WY	USC00484080	May 11	September 23	133 days
Lovell, WY	USC00485770	May 9	September 29	142 days
Shell, WY	USC00488124	May 16	September 24	130 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

Big Horn 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 — 4b–5a

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 4b 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 4b, 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.