What zone 5a means for Casper
Hardiness zones are based on the average of the coldest night of each winter over 30 years (1991 to 2020). In zone 5a, that average is -20 to -15°F (-29 to -26°C). Plants labeled hardy to zone 5a or colder should survive a typical Casper winter. A plant rated only to a warmer zone will need a sheltered spot, a pot you can bring inside, or treating as an annual.
How Casper compares with the rest of Wyoming
Wyoming runs from zone 4a to zone 5b on the 2023 map. About 58% of the state's ZIP codes share Casper's zone 5a. Gardeners in colder parts of the state may need hardier plants, while those in warmer parts can grow some plants that would struggle here.
Frost dates in Casper
These are the median dates of the last and first 32°F freeze from NOAA's 1991 to 2020 climate normals, using the weather station closest to Casper (Casper 1Sw, about 1 km away). Half of years have a later last frost, so tender plants are safest a week or two after the date. Your own garden can differ with elevation and shelter: check your exact ZIP code above.
Vegetable planting calendar for Casper
Purdue Extension groups vegetables by how much frost they can take and times planting from the average last spring frost. Applied to Casper's last frost of May 10:
| Group | Plant outdoors | Crops |
|---|---|---|
| Hardy crops (tolerate a hard frost) 4 to 6 weeks before the average last spring frost | March 29 to April 12 | Asparagus, broccoli, Brussels sprouts, cabbage, collards, horseradish, kale, kohlrabi, leek, mustard, onion, peas, potato, radish, rhubarb, spinach, turnip |
| Semi-hardy crops (tolerate a light frost) 2 to 4 weeks before the average last spring frost | April 12 to April 26 | Beet, carrot, cauliflower, celery, chard, Chinese cabbage, lettuce, mustard, parsnip |
| Tender crops (damaged by frost) after the average last spring frost, once nights stay above 50°F | From May 10 | Bean, sweet corn, tomato |
| Very tender crops (warm season) at least 2 weeks after the average last spring frost, once nights stay above 60 to 65°F | From May 24 | Cucumber, eggplant, melons, okra, pepper, pumpkin, squash, sweet potato |
Spring planting for direct seeding or transplants. A late cold snap can still happen, so watch the forecast and protect tender plants. Want today's answer for your ZIP code? Use what to plant now.
Sources: NOAA NCEI U.S. Climate Normals 1991 to 2020; Purdue Extension, Indiana Vegetable Planting Calendar (HO-186-W).
Choosing plants for zone 5a
When you shop, look for the hardiness range on the tag or in the catalog, such as "zones 4 to 9". Pick perennials, shrubs and trees whose range includes 5a. If you are set on a plant rated only to a warmer zone, plant it in a sheltered spot against a south-facing wall, mulch the roots before winter, or grow it in a container you can move into a garage. Zones only cover winter cold, so also check sun, water and soil needs. More in how to read a plant tag.
Casper ZIP codes and zones
ZIP codes GeoNames assigns to Casper, which can include PO box ZIP codes.
Other cities in Wyoming
Frequently asked questions
When is the last frost in Casper?
The median last spring frost (32°F) near Casper is May 10, and the median first fall frost is September 29, based on NOAA 1991 to 2020 climate normals.
What planting zone is Casper in?
Casper, WY is in USDA plant hardiness zone 5a. Zone 5a means an average coldest winter night of -20 to -15°F (-29 to -26°C), based on the 2023 USDA map.
Did Casper's zone change in 2023?
The 2023 USDA map uses weather data from 1991 to 2020. The USDA says about half of the country shifted to the next warmer half zone compared with the 2012 map, while the rest stayed in the same half zone.
Zones: 2023 USDA Plant Hardiness Zone Map ZIP code listings, PRISM Climate Group, Oregon State University. Place names: GeoNames (CC BY 4.0). Not the official USDA map. Our data.