State guide
Planting zones in Wyoming
Wyoming spans USDA zones 4a to 5b across its 176 ZIP codes, so there is no single zone for the state and anyone who gives you one is rounding. 58% of its ZIP codes are zone 5a; the rest are not.
Your ZIP code
Get the exact answer for your address
Everything above describes 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.
Which zone you are in depends where you are
Wyoming covers 4 hardiness zones. A guide that gives the state one zone has picked whichever is largest and rounded everyone else into it — which is fine for the 58% in zone 5a and wrong for the other 42%. Here is the actual split, by ZIP code.
| Zone | ZIP codes | Share | |
|---|---|---|---|
| 5a | 102 | 58% | |
| 4b | 40 | 23% | |
| 5b | 24 | 14% | |
| 4a | 10 | 6% |
Zones are published per ZIP code, so yours is exact even though the state's is not. The hardiness tool will tell you which one you are in.
Your freeze dates
Those are the earliest and latest medians among the 129 stations in Wyoming with an ordinary freeze window — not an average, and not one station standing in for the rest. Half of years freeze later than a station's own median.
Your growing season
NOAA publishes a growing-season length for each station, and across the 129 stations in Wyoming it runs 63–164 days . That figure is published, not computed from the two freeze dates — subtracting one from the other gives the wrong answer wherever a season crosses New Year. Mean summer high (June–August) runs 72–89 °F , below the 90 °F point where cool-season crops reliably bolt.
The ends of each range, named
A range with no station behind it cannot be checked, and Wyoming has too many stations to table them all. So every figure above is reported here with the station standing at each end of it, by name and NOAA ID. No station on this page represents Wyoming — these are its edges, which is a different claim.
| Measure | Earliest / lowest | Station | Latest / highest | Station |
|---|---|---|---|---|
| Last spring freeze | April 28 | Basin, WY USC00480540 | June 24 | Moose 1 Nne, WY USW00004131 |
| First fall freeze | August 28 | Moose 1 Nne, WY USW00004131 | October 10 | Basin, WY USC00480540 |
| Growing season | 63 days | Moose 1 Nne, WY USW00004131 | 164 days | Basin, WY USC00480540 |
| Mean summer high | 72 °F | Sundance 8 Nnw, WY USW00094088 | 89 °F | Basin, WY USC00480540 |
These are medians, not averages — NOAA publishes freeze dates as a probability distribution, and half of years freeze later than the date shown.
When to start seeds in Wyoming
Every spring job for 63 crop dates, counted from this state's own last spring freeze. Each is a range across all 129 stations — the earliest and latest that job falls anywhere in Wyoming — because no one station speaks for a whole state. The ranges are wide on purpose: that width is the state.
| Crop | Job | When | Offset |
|---|---|---|---|
| Green Onions | Start indoors | March 3 – April 29 | 8 weeks before |
| Peppers | Start indoors | March 3 – April 29 | 8 weeks before |
| Broccoli | Start indoors | March 17 – May 13 | 6 weeks before |
| Cabbage | Start indoors | March 17 – May 13 | 6 weeks before |
| Collards | Start indoors | March 17 – May 13 | 6 weeks before |
| Kale | Start indoors | March 17 – May 13 | 6 weeks before |
| Leaf Lettuce | Start indoors | March 17 – May 13 | 6 weeks before |
| Peas | Direct sow | March 17 – May 13 | 6 weeks before |
| Spinach | Direct sow | March 17 – May 13 | 6 weeks before |
| Sweet Potato | Start indoors | March 17 – May 13 | 6 weeks before |
| Tomatoes | Start indoors | March 17 – May 13 | 6 weeks before |
| Bok Choy | Start indoors | March 24 – May 20 | 5 weeks before |
| Kohlrabi | Start indoors | March 24 – May 20 | 5 weeks before |
| Swiss Chard | Start indoors | March 24 – May 20 | 5 weeks before |
| Arugula | Direct sow | March 31 – May 27 | 4 weeks before |
| Baby Salad Greens | Direct sow | March 31 – May 27 | 4 weeks before |
| Beets | Direct sow | March 31 – May 27 | 4 weeks before |
| Green Onions | Direct sow | March 31 – May 27 | 4 weeks before |
| Mustard Greens | Direct sow | March 31 – May 27 | 4 weeks before |
| Okra | Start indoors | March 31 – May 27 | 4 weeks before |
| Radishes | Direct sow | March 31 – May 27 | 4 weeks before |
| Turnips | Direct sow | March 31 – May 27 | 4 weeks before |
| Cabbage | Set out | April 7 – June 3 | 3 weeks before |
| Carrots | Direct sow | April 7 – June 3 | 3 weeks before |
| Collards | Direct sow | April 7 – June 3 | 3 weeks before |
| Collards | Set out | April 7 – June 3 | 3 weeks before |
| Cucumbers | Start indoors | April 7 – June 3 | 3 weeks before |
| Green Onions | Set out | April 7 – June 3 | 3 weeks before |
| Kale | Direct sow | April 7 – June 3 | 3 weeks before |
| Kale | Set out | April 7 – June 3 | 3 weeks before |
| Kohlrabi | Direct sow | April 7 – June 3 | 3 weeks before |
| Kohlrabi | Set out | April 7 – June 3 | 3 weeks before |
| Leaf Lettuce | Direct sow | April 7 – June 3 | 3 weeks before |
| Pumpkins | Start indoors | April 7 – June 3 | 3 weeks before |
| Summer Squash | Start indoors | April 7 – June 3 | 3 weeks before |
| Winter Squash | Start indoors | April 7 – June 3 | 3 weeks before |
| Zucchini | Start indoors | April 7 – June 3 | 3 weeks before |
| Bok Choy | Direct sow | April 14 – June 10 | 2 weeks before |
| Bok Choy | Set out | April 14 – June 10 | 2 weeks before |
| Broccoli | Set out | April 14 – June 10 | 2 weeks before |
| Cilantro | Direct sow | April 14 – June 10 | 2 weeks before |
| Leaf Lettuce | Set out | April 14 – June 10 | 2 weeks before |
| Swiss Chard | Direct sow | April 14 – June 10 | 2 weeks before |
| Swiss Chard | Set out | April 14 – June 10 | 2 weeks before |
| Dill | Direct sow | April 21 – June 17 | 1 week before |
| Bush Beans | Direct sow | May 5 – July 1 | 1 week after |
| Cucumbers | Set out | May 5 – July 1 | 1 week after |
| Pumpkins | Direct sow | May 5 – July 1 | 1 week after |
| Pumpkins | Set out | May 5 – July 1 | 1 week after |
| Summer Squash | Direct sow | May 5 – July 1 | 1 week after |
| Summer Squash | Set out | May 5 – July 1 | 1 week after |
| Sweet Corn | Direct sow | May 5 – July 1 | 1 week after |
| Tomatoes | Set out | May 5 – July 1 | 1 week after |
| Winter Squash | Direct sow | May 5 – July 1 | 1 week after |
| Winter Squash | Set out | May 5 – July 1 | 1 week after |
| Zucchini | Direct sow | May 5 – July 1 | 1 week after |
| Zucchini | Set out | May 5 – July 1 | 1 week after |
| Cucumbers | Direct sow | May 12 – July 8 | 2 weeks after |
| Okra | Direct sow | May 12 – July 8 | 2 weeks after |
| Okra | Set out | May 12 – July 8 | 2 weeks after |
| Peppers | Set out | May 12 – July 8 | 2 weeks after |
| Southern Peas | Direct sow | May 12 – July 8 | 2 weeks after |
| Sweet Potato | Set out | May 12 – July 8 | 2 weeks after |
The week offsets are conventional extension guidance and vary by variety; the freeze dates they are counted from are measured. For a single date rather than a range, run when do I start my seeds? with your own ZIP code.
What survives the winter changes across Wyoming
Of 74 perennial fruits, nuts, berries, vegetables and herbs, 48 come through the winter in zone 5a and only 34 in zone 4a. Winter hardiness runs on the zone alone, so each row below is exact for the ZIP codes in it.
| Zone | ZIPs | Survive | Fail for being too warm |
|---|---|---|---|
| 4a | 10 | 34 of 74 | 0 |
| 4b | 40 | 34 of 74 | 0 |
| 5a | 102 | 48 of 74 | 0 |
| 5b | 24 | 48 of 74 | 0 |
The best zone in Wyoming is 5a, which is not its mildest — 5b is. The count peaks in the middle and falls both ways, because the warm end loses plants to insufficient winter chill and summer heat rather than to cold. Most temperate fruit needs a documented number of hours below about 45 °F to break dormancy and set a crop, so an apple fails in a winter that is too warm; currants and rhubarb cook in the heat that comes with it. See the full list with reasons.
Your own ZIP
Work out your own dates
Each of these takes a ZIP code and answers for that ZIP alone, citing the station it used and how far away it is. There is a ZIP box in the header of every page.
- What survives my winter?
Runs on the hardiness zone, so it answers exactly for your ZIP code rather than for Wyoming as a whole — 74 perennial fruits, berries, vegetables and herbs.
- When do I start my seeds?
Dates every spring job from your own last freeze — sow indoors, set out, direct sow.
- When do I sow the next round?
How often each crop is worth re-sowing, and when the next sowing is due.
- What can I still plant?
Counts the growing days left before your first fall freeze, crop by crop.
Metro areas in Wyoming
2 metro areas here have its own page, with the freeze dates from every station serving it, a spring calendar built from those stations, and every ZIP code in it listed with that ZIP code's exact zone and nearest station.
- Casper, WY Zone 5a
- Cheyenne, WY Zones 5a–5b
Counties in Wyoming
13 countys here have its own page, listing every ZIP code in it with that ZIP code's exact zone and nearest station. These are the smaller places outside the metro areas above — where most of Wyoming's ZIP codes actually are.
- Lincoln County, WY Zones 4a–5b
- Big Horn County, WY Zones 4b–5a
- Fremont County, WY Zones 4b–5a
- Carbon County, WY Zones 4a–5b
- Sheridan County, WY Zones 4b–5a
- Sweetwater County, WY Zones 4a–5b
- Albany County, WY Zones 4a–5b
- Goshen County, WY Zone 5a
- Campbell County, WY Zones 4b–5a
- Crook County, WY Zones 4b–5a
- Park County, WY Zones 4b–5a
- Sublette County, WY Zones 4a–4b
- Platte County, WY Zone 5a
Other states to compare
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
The hardiness zone is the USDA 2023 Plant Hardiness Zone Map, published per ZIP code by PRISM at Oregon State. The freeze dates, growing seasons and summer highs are NOAA's 1991–2020 Climate Normals, read from every station in Wyoming. Which ZIP codes are in Wyoming comes from the Census ZIP-to-county relation, since a county's federal code begins with its state's. Nothing here is estimated.
This page names no single station for Wyoming on purpose. Picking one to represent a state sounds reasonable and is not — the same reason the metro pages refuse it, only more so at this size. Instead every range names the station at each end, so you can check both without either one being made to speak for the state.