When to plant in Casper, WY
USDA Zone 5aCasper, Wyoming frost dates, USDA zone, and a full-year planting calendar, drawn from the nearest NOAA station and tuned to the local season.
Zone 5a means Casper sees real winter cold, but a good range of perennials survive; the frost dates above govern when annual vegetables go out.
Frost probability
CASPER WWTP · 1991–2020The date the last spring and first fall frost occur, by threshold and probability. A 90% date is later in spring — and earlier in fall — than a 10% date; the 50% · 32°F row is what most gardeners plan around. These are Casper’s own odds, recorded at CASPER WWTP.
| Threshold | SPRING 10% | SPRING 50% | SPRING 90% | FALL 10% | FALL 50% | FALL 90% |
|---|---|---|---|---|---|---|
| 36°F | Jun 6 | May 23 | May 11 | Sep 6 | Sep 19 | Oct 2 |
| 32°F | May 24 | May 10 | Apr 30 | Sep 14 | Sep 29 | Oct 12 |
| 28°F | May 14 | May 1 | Apr 17 | Sep 21 | Oct 6 | Oct 23 |
Download this table as CSV ↓ — every threshold and probability, plus this city’s planting-window dates.
What to plant now
TODAY · JULY 19Full-year planting calendar
Each bar is the exact window to take a planting action in Casper, drawn to the day from the local frost dates. The dashed line is today.
Nearby weather stations
3 within 13 km · complete 32°F normalsWhen stations disagree by more than a few days, that spread is real microclimate variation — elevation, water, urban heat. Judge which station best matches your own yard.
Casper planting FAQ
When is the last spring frost in Casper, WY?
Casper's average last spring frost falls near May 10 — the 50% mark at 32°F in the 1991–2020 normals. Hold tender transplants until the risk has passed, then plant out.
When is the first fall frost in Casper, WY?
In Casper, the first 32°F freeze of fall lands around September 29 on average. Time your last harvests and any season-extension cover before it.
What hardiness zone is Casper in?
Casper is in USDA hardiness zone 5a. In zone 5a, winters are cold — pick cold-hardy varieties and protect tender crops.
How long is the growing season in Casper?
There are roughly 142 frost-free days in Casper (a short growing season), running from the average last frost around May 10 to the first fall frost near September 29.
When should I plant tomatoes in Casper?
In Casper, start tomato seeds indoors around March 15–March 29, then transplant seedlings outdoors around May 17 once the danger of frost has passed.
Never miss a window in Casper
An email when it’s time to start seeds, transplant, and sow — timed to Casper’s frost dates. Double opt-in, one-click unsubscribe, no spam.
Nearby cities
8 within reach- Riverton · 169 km
- Gillette · 172 km
- Laramie · 180 km
- Sheridan · 223 km
- Cheyenne · 228 km
- Scottsbluff · 244 km
- Wellington · 262 km
- Steamboat Springs · 266 km
Frost dates recorded at CASPER WWTP, 3 km from the city center · 1991–2020 NOAA climate normals · zone from the USDA/PRISM 2023 map. How we compute this.
BlissGarden. "When to Plant in Casper, WY — Frost Dates & Zone 5a." Frost normals: NOAA NCEI U.S. Climate Normals 1991–2020, station USC00481569. Retrieved from https://blissgarden.com/wyoming/casper.