Casper, WY Frost Dates & Growing Season

The two dates every Casper garden is planned around, plus ready-computed planting windows for the most popular crops.

Last spring frost
May 10
~50% chance of frost after
First fall frost
Sep 29
~50% chance of frost before
Growing season
142 days
frost-free stretch
USDA zone
5a
2023 hardiness map
Risky (1 year in 10)MedianSafe (9 years in 10)
Last spring frost Apr 30 May 10 May 24
First fall frost Oct 12 Sep 29 Sep 14
Hard freeze (28°F), median last May 1 · first Oct 6

Computed from NOAA 1991–2020 climate normals at the Casper Wwtp station (2 km from central Casper). "Safe" means frost past that date happens only about one year in ten. Your exact garden can still run days either way with elevation and terrain — check your own ZIP with the frost date lookup.

Planting windows for Casper

Computed from Casper's own frost dates. Click any crop for the full zone-5 growing guide — varieties, spacing, fall plantings, and more.

CropStart seeds indoorsTransplantDirect sow
🍅 Tomatoes Mar 15 – Mar 29 May 17 – May 24
🫑 Peppers Mar 1 – Mar 15 May 24 – May 31
🥬 Lettuce Mar 29 – Apr 12 Apr 12 – Apr 26 Apr 12 – May 10
🫛 Peas Mar 29 – Apr 12
🥕 Carrots Apr 19 – May 10
🥦 Broccoli Mar 22 – Apr 5 Apr 19 – May 3
🥬 Kale Mar 29 – Apr 12 Apr 12 – Apr 26 Apr 12 – Apr 26
🥒 Cucumbers Apr 12 – Apr 19 May 17 – May 24 May 17 – May 24
🥒 Zucchini Apr 12 – Apr 19 May 17 – May 24 May 17 – May 24
🫘 Green Beans (Bush) May 17 – May 24
🌽 Sweet Corn May 17 – May 24
🌿 Basil Mar 29 – Apr 12 May 17 – May 24 May 24 – May 31
🧄 Garlic Fall: Aug 18 – Sep 15

Want this for all 50 crops, or as a printable seed-shelf schedule? Use the planting calendar and the seed starting scheduler — both can use Casper's dates automatically after a lookup.

Reading the season in Casper

At about 142 frost-free days, Casper rewards efficiency: start warm-season crops indoors, favor short-season varieties, and lean on cold-tolerant crops — peas, kale, roots — that shrug off the shoulder-season frosts on either end.

Frequently asked questions

When is the last frost in Casper, WY?

The average last spring frost in Casper is around May 10, based on 1991–2020 climate normals. That's a median — about half of years see a later frost, so tender crops are safest going out a week or two after this date.

When is the first frost in Casper, WY?

The average first fall frost in Casper arrives around Sep 29. Crops still in the garden need to mature before then, and frost-tender plants need harvesting or protection as the date approaches.

How long is the growing season in Casper?

About 142 frost-free days on average, from May 10 to Sep 29. That favors short-season varieties and transplants for warm-season crops, with cool-season vegetables doing the heavy lifting in spring and fall.

What USDA zone is Casper in?

USDA zone 5a on the 2023 Plant Hardiness Zone Map. Note that zones describe winter cold, not frost timing — these frost dates are the numbers to plan plantings around.