What does USDA hardiness zone 4b mean in Wyoming?

Zone 4b means an average annual extreme minimum winter temperature of −25 to −20 °F — the standard USDA measure of which perennials survive winter. 26 locations in Wyoming fall in this zone. It does not set planting dates; see the frost calendar below for that.

Where in Wyoming's zone 4b is the growing season longest?

Basin runs the longest season on this page at about 164 days; Hoback is shortest at about 70 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.

When should I plant tomatoes in Wyoming's zone 4b?

Using Sundance's frost dates (this page's median-season location): start seeds indoors about Mar 26 – Apr 9, then transplant outside about May 28 – Jun 4. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.

Does every location in Wyoming's zone 4b have the same frost dates?

No — they do not all share a weather station, so frost dates vary by a week or more across the 26 locations listed (see the table above for each location's own dates).

USDA zone 4b in Wyoming

−25 to −20 °F avg. annual extreme minimum · 26 locations in this group · NOAA 1991–2020 normals

USDA plant hardiness zone 4b covers 26 locations across Wyoming (average annual extreme minimum −25 to −20 °F): Arvada, WY, Baggs, WY, Basin, WY, Bondurant, WY, Burlington, WY, Cora, WY, and 20 more. Average last spring frost across this group ranges April 28 (Basin) to June 20 (Hoback), and growing seasons run 70–164 days (Hoback to Basin) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Wyoming location's own frost dates; the printable planting calendar uses Sundance, this group's median-season location.

USDA zone: 4b−25 to −20 °F
Last frost range: Apr 28–Jun 20avg, 32°F
First frost range: Aug 31–Oct 10avg, 32°F
Growing season range: 70–164days

Locations in this group

Every location below shares this zone and a nearby weather station, but keeps its own frost dates — find your town for its own numbers, or use the ZIP planner on the home page for an instant personalized answer.

Own frost dates per location.
Location	Also covers	Nearest station	Last frost	First frost	Season (days)
Arvada	Clearmont	Leiter 9n	May 14	Sep 30	137
Baggs	Dixon	Baggs	Jun 1	Sep 18	108
Basin	Manderson	Basin	Apr 28	Oct 10	164
Bondurant	Grover, Auburn	Afton	Jun 20	Sep 1	71
Burlington	—	Emblem	May 12	Sep 28	136
Cora	Dubois, Pinedale	Burris	Jun 1	Sep 14	104
Greybull	—	Greybull S Big Horn Ap	May 4	Oct 1	149
Hoback	Teton	Moose	Jun 20	Aug 31	70
Hulett	—	Hulett	May 17	Sep 23	128
Jeffrey	—	Jeffrey City	Jun 1	Sep 13	104
Kemmerer	—	Randolph	Jun 14	Sep 1	76
Kemmerer	Granger, Opal	Church Buttes Gas Plt	May 25	Sep 27	124
Kirby	—	Thermopolis	May 5	Oct 5	152
Lance Creek	—	Lance Creek 11nne	May 17	Sep 25	129
Meeteetse	—	Cody 12se	May 24	Sep 15	114
Newcastle	—	Newcastle	May 13	Oct 3	143
Parkman	—	Shell	May 16	Sep 24	130
Pine Haven	Hulett	Devils Twr #2	May 23	Sep 20	118
Rock River	—	Medicine Bow	Jun 1	Sep 8	97
Shoshoni	—	Boysen Dam	May 5	Oct 7	153
Sleepy Hollow	—	Gillette 4se	May 15	Oct 1	136
Sundance *	—	Sundance	May 21	Sep 25	124
Table Rock	—	Wamsutter	Jun 5	Sep 14	101
Upton	Osage	Upton	May 20	Sep 23	123
Woods Landing-Jelm	—	Laramie Rgnl Ap	Jun 2	Sep 15	102
Worland	—	Worland	May 4	Oct 1	149

* Sundance is this group's median-season location — the calendar below is computed from its data.

Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.

Planting calendar (Sundance, representative)

Computed from Sundance's average frost dates — the median-season location in this Wyomingzone 4b group. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees — your own location's dates may run a week or two earlier or later (see the table above).

Crop

JanFebMarAprMayJunJulAugSepOctNovDec

Tomato

Pepper

Cucumber

Summer squash / zucchini

Start indoors
Plant out
Fall sowing
First harvest

Planting windows for Sundance (Wyoming, zone 4b), this group's representative location.
Crop	Frost tolerance	Start indoors	Plant out	First harvest	Fall planting	Season fit
Tomato	Tender	Mar 26 – Apr 9	May 28 – Jun 4	Jul 27 – Aug 16	—	matures comfortably
Pepper	Very tender	Mar 12 – Mar 26	Jun 4 – Jun 11	Aug 3 – Sep 2	—	matures comfortably
Cucumber	Tender	Apr 23 – Apr 30	May 28 – Jun 4	Jul 17 – Aug 6	—	matures comfortably
Summer squash / zucchini	Tender	—	May 28 – Jun 4	Jul 12 – Jul 27	—	matures comfortably
Bush bean	Tender	—	May 28 – Jun 4	Jul 17 – Jul 27	Jul 27 – Aug 6	matures comfortably
Sweet corn	Tender	—	May 21 – Jun 4	Jul 20 – Aug 19	—	matures comfortably
Basil	Very tender	Apr 9 – Apr 23	May 28 – Jun 4	Jun 27 – Jul 12	—	matures comfortably
Lettuce	Half-hardy	Apr 9 – Apr 23	Apr 23 – May 7	Jun 7 – Jun 22	Jul 13 – Jul 28	matures comfortably
Pea	Hardy	—	Apr 9 – Apr 23	Jun 3 – Jun 18	Jul 3 – Jul 18	matures comfortably
Spinach	Hardy	—	Apr 9 – Apr 23	May 19 – May 29	Jul 23 – Aug 2	matures comfortably
Carrot	Half-hardy	—	Apr 30 – May 7	Jun 29 – Jul 19	Jun 23 – Jul 13	matures comfortably
Broccoli	Half-hardy	Mar 26 – Apr 9	Apr 23 – May 7	Jun 17 – Jul 7	Jun 28 – Jul 18	matures comfortably

Which crops fit this growing season

Using Sundance's own 124-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 12 of 12 crops mature here with comfortable margin. A different location in the table above with a longer or shorter season will get a different mix — the ZIP planner on the home page gives your own.

Frost & freeze dates (Sundance)

From NOAA's 1991–2020 Climate Normals at station USC00488705. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 — the conservative date to plant after or harvest before.

Freeze probabilities by temperature threshold (MM/DD, NOAA 1991–2020), Sundance.
Threshold	Last spring — avg	Last spring — 90%-safe	First fall — avg	First fall — 90%-safe	Season (days)
36°F	Jun 1	Jun 24	Sep 16	Sep 29	101
32°F (freeze)	May 21	Jun 5	Sep 25	Oct 8	124
28°F	May 9	May 23	Oct 4	Oct 19	145
24°F	Apr 29	May 12	Oct 12	Oct 26	166

Growing degree days

Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. This group's median GDD (base 50°F) across all 26 locations is 2,151; Sundance's own reading is shown below.

Annual growing degree days for Sundance (°F·days, NOAA 1991–2020).
Model	°F·days	Used for
Base 50°F (warm-season)	1,959	standard warm-season base (tomato, corn, beans)
Base 40°F (cool-season)	3,722	cool-season crops (brassicas, greens)

Hardiness zone 4b in Wyoming

Zone 4b means an average annual extreme minimum winter temperature of about −25 to −20 °F on the USDA's 2023 map — the number that tells you which perennials, shrubs, and trees reliably survive an average winter here. It does not set your planting dates, which come from the frost calendar above. Wyoming spans 4 hardiness zones in this dataset — see all Wyoming locations for the full range, including zones4a, 5a, 5b.

Explore zone 4b in other states at zone 4b, or see all USDA hardiness zones.

Frequently asked questions

What does USDA hardiness zone 4b mean in Wyoming?: Zone 4b means an average annual extreme minimum winter temperature of −25 to −20 °F — the standard USDA measure of which perennials survive winter. 26 locations in Wyoming fall in this zone. It does not set planting dates; see the frost calendar below for that.
Where in Wyoming's zone 4b is the growing season longest?: Basin runs the longest season on this page at about 164 days; Hoback is shortest at about 70 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.
When should I plant tomatoes in Wyoming's zone 4b?: Using Sundance's frost dates (this page's median-season location): start seeds indoors about Mar 26 – Apr 9, then transplant outside about May 28 – Jun 4. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.
Does every location in Wyoming's zone 4b have the same frost dates?: No — they do not all share a weather station, so frost dates vary by a week or more across the 26 locations listed (see the table above for each location's own dates).

Sources & method

Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020, one reading per location's own nearest station (see the table above). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to each location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.