Gardening in Casper, WY
Every ZIP code in this metro is USDA zone 5a. That is unusual — most metros span several zones — and it means the one number people usually look up is the same wherever you are here.
Your freeze dates
Those are the earliest and latest medians among the 7 stations serving this metro — not an average, and not one station standing in for the rest. Half of years freeze later than a station's own median.
The spread is the point. Even in a metro that is one hardiness zone throughout, its stations disagree about the last spring freeze. Hardiness zone and frost date measure different things — a zone is the average annual coldest night, a freeze date is when the season turns — and a place can be uniform in one and varied in the other. Use the tools below with your own ZIP rather than the ends of this range.
Your growing season
NOAA publishes a growing-season length for each station, and across the 7 stations serving Casper, WY it runs 115–148 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 82–85 °F , below the 90 °F point where cool-season crops reliably bolt.
When to start seeds in Casper, WY
Every spring job for 63 crop dates, counted from this metro's own last spring freeze. Each is a range across all 7 stations — the earliest and latest that job falls anywhere in the metro — because no one station speaks for the whole area.
| Crop | Job | When | Offset |
|---|---|---|---|
| Green Onions | Start indoors | March 14 – April 4 | 8 weeks before |
| Peppers | Start indoors | March 14 – April 4 | 8 weeks before |
| Broccoli | Start indoors | March 28 – April 18 | 6 weeks before |
| Cabbage | Start indoors | March 28 – April 18 | 6 weeks before |
| Collards | Start indoors | March 28 – April 18 | 6 weeks before |
| Kale | Start indoors | March 28 – April 18 | 6 weeks before |
| Leaf Lettuce | Start indoors | March 28 – April 18 | 6 weeks before |
| Peas | Direct sow | March 28 – April 18 | 6 weeks before |
| Spinach | Direct sow | March 28 – April 18 | 6 weeks before |
| Sweet Potato | Start indoors | March 28 – April 18 | 6 weeks before |
| Tomatoes | Start indoors | March 28 – April 18 | 6 weeks before |
| Bok Choy | Start indoors | April 4 – April 25 | 5 weeks before |
| Kohlrabi | Start indoors | April 4 – April 25 | 5 weeks before |
| Swiss Chard | Start indoors | April 4 – April 25 | 5 weeks before |
| Arugula | Direct sow | April 11 – May 2 | 4 weeks before |
| Baby Salad Greens | Direct sow | April 11 – May 2 | 4 weeks before |
| Beets | Direct sow | April 11 – May 2 | 4 weeks before |
| Green Onions | Direct sow | April 11 – May 2 | 4 weeks before |
| Mustard Greens | Direct sow | April 11 – May 2 | 4 weeks before |
| Okra | Start indoors | April 11 – May 2 | 4 weeks before |
| Radishes | Direct sow | April 11 – May 2 | 4 weeks before |
| Turnips | Direct sow | April 11 – May 2 | 4 weeks before |
| Cabbage | Set out | April 18 – May 9 | 3 weeks before |
| Carrots | Direct sow | April 18 – May 9 | 3 weeks before |
| Collards | Direct sow | April 18 – May 9 | 3 weeks before |
| Collards | Set out | April 18 – May 9 | 3 weeks before |
| Cucumbers | Start indoors | April 18 – May 9 | 3 weeks before |
| Green Onions | Set out | April 18 – May 9 | 3 weeks before |
| Kale | Direct sow | April 18 – May 9 | 3 weeks before |
| Kale | Set out | April 18 – May 9 | 3 weeks before |
| Kohlrabi | Direct sow | April 18 – May 9 | 3 weeks before |
| Kohlrabi | Set out | April 18 – May 9 | 3 weeks before |
| Leaf Lettuce | Direct sow | April 18 – May 9 | 3 weeks before |
| Pumpkins | Start indoors | April 18 – May 9 | 3 weeks before |
| Summer Squash | Start indoors | April 18 – May 9 | 3 weeks before |
| Winter Squash | Start indoors | April 18 – May 9 | 3 weeks before |
| Zucchini | Start indoors | April 18 – May 9 | 3 weeks before |
| Bok Choy | Direct sow | April 25 – May 16 | 2 weeks before |
| Bok Choy | Set out | April 25 – May 16 | 2 weeks before |
| Broccoli | Set out | April 25 – May 16 | 2 weeks before |
| Cilantro | Direct sow | April 25 – May 16 | 2 weeks before |
| Leaf Lettuce | Set out | April 25 – May 16 | 2 weeks before |
| Swiss Chard | Direct sow | April 25 – May 16 | 2 weeks before |
| Swiss Chard | Set out | April 25 – May 16 | 2 weeks before |
| Dill | Direct sow | May 2 – May 23 | 1 week before |
| Bush Beans | Direct sow | May 16 – June 6 | 1 week after |
| Cucumbers | Set out | May 16 – June 6 | 1 week after |
| Pumpkins | Direct sow | May 16 – June 6 | 1 week after |
| Pumpkins | Set out | May 16 – June 6 | 1 week after |
| Summer Squash | Direct sow | May 16 – June 6 | 1 week after |
| Summer Squash | Set out | May 16 – June 6 | 1 week after |
| Sweet Corn | Direct sow | May 16 – June 6 | 1 week after |
| Tomatoes | Set out | May 16 – June 6 | 1 week after |
| Winter Squash | Direct sow | May 16 – June 6 | 1 week after |
| Winter Squash | Set out | May 16 – June 6 | 1 week after |
| Zucchini | Direct sow | May 16 – June 6 | 1 week after |
| Zucchini | Set out | May 16 – June 6 | 1 week after |
| Cucumbers | Direct sow | May 23 – June 13 | 2 weeks after |
| Okra | Direct sow | May 23 – June 13 | 2 weeks after |
| Okra | Set out | May 23 – June 13 | 2 weeks after |
| Peppers | Set out | May 23 – June 13 | 2 weeks after |
| Southern Peas | Direct sow | May 23 – June 13 | 2 weeks after |
| Sweet Potato | Set out | May 23 – June 13 | 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 lives through a zone 5a winter
Winter hardiness runs on the zone alone, so this one is exact for the whole of Casper, WY rather than a range. Of 74 perennial fruits, nuts, berries, vegetables and herbs, 48 come through a zone 5a winter — the other 26 fail, and not all of them for cold.
Among them: Cranberry, Honeyberry, Lingonberry, Apple, Aronia, Black Currant, Elderberry, Gooseberry. See the full list with reasons.
The 7 stations behind these numbers
Every figure above comes from these, and each is named so you can check it. Distances vary by ZIP code, so the tools report yours rather than this page guessing.
| Station | NOAA ID | Last spring freeze | First fall freeze | Season |
|---|---|---|---|---|
| Casper 1Sw, WY | USC00481572 | May 12 | October 1 | 143 days |
| Casper Natrona Co AP, WY | USW00024089 | May 26 | September 22 | 117 days |
| Casper WWTP, WY | USC00481569 | May 10 | September 29 | 138 days |
| Midwest, WY | USC00486195 | May 22 | September 22 | 121 days |
| Pathfinder Dam, WY | USC00487105 | May 9 | October 7 | 148 days |
| Powder River #2, WY | USC00487376 | May 23 | September 20 | 121 days |
| Powder Rvr (School), WY | USC00487375 | May 30 | September 22 | 115 days |
These are medians, not averages — NOAA publishes freeze dates as a probability distribution, and half of years freeze later than the date shown.
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 for all of Casper, WY at once — zone 5a across 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.
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 are NOAA's 1991–2020 Climate Normals, read from every station whose normals cover a ZIP code in this metro. Nothing here is estimated, and no station stands in for another.
This page names no single station on purpose. Picking one to represent a metro sounds reasonable and is not: the station serving the most ZIP codes is an artifact of where ZIP centroids happen to fall, and it selects a lock on the Monongahela for Pittsburgh and a far southern suburb for Chicago. A range across every station is true; a single cited date for a whole metro is not.