Casper, Wyoming Planting Dates, Frost Dates & Growing Season

Growing Season Snapshot

Casper’s exposed, high-plains feel keeps gardening honest. The city can produce well in summer, but it does not hand out much extra margin, so crops that need a long, stable finish tend to be less dependable than the midday warmth might imply.

Typical last spring frost May 26

Typical first fall frost September 22

Typical frost-free days 119

GDD left on May 15 (base 50) 1968

These season boundaries are climate normals, not a forecast. A 50% frost date means a 32°F frost arrives by that date in about half of years — and later in about half. Treat these dates as planning anchors, not guarantees.

Best next step: Use the Growing Degree Day Planner to test a specific crop and planting date for your exact location.

Casper Spring Planting Windows

A practical guide to when planting usually works in Casper. These windows are based on climate normals (not a forecast) and line up with the 50% last spring frost and typical early-season heat.

Cool-season / early window Cold-tolerant crops that usually handle cooler spring conditions better.
Spinach	April 28 – May 12	direct sow	Excellent fit
Peas	April 28 – May 12	direct sow	Excellent fit
Lettuce	May 5 – May 19	direct sow / transplant	Excellent fit
Carrots	May 5 – May 19	direct sow	Excellent fit
Beets	May 5 – May 19	direct sow	Excellent fit
Onions	May 5 – May 19	sets / transplants	Excellent fit
Broccoli	May 12 – May 26	transplant	Excellent fit
Cabbage	May 12 – May 26	transplant	Excellent fit
Cauliflower	May 12 – May 26	transplant	Excellent fit
Potatoes	May 12 – May 26	plant seed potatoes	Excellent fit
Main warm-season window Crops that usually do best once frost risk fades and the season starts opening up more fully.
Beans	May 26 – June 9	direct sow	Strong fit
Sweet Corn	May 31 – June 10	direct sow	Strong fit
Tomatoes	June 4 – June 14	transplant	Strong fit
Cucumbers	June 4 – June 14	direct sow / transplant	Excellent fit
Zucchini	June 4 – June 14	direct sow / transplant	Excellent fit
Peppers	June 11 – June 21	transplant	Strong fit

How to use this: aim for the earlier part of each window for the most reliable results. Later planting can still work, but it usually depends more on variety maturity, warmer microclimates, and simple protection like row cover or low tunnels.

Missed Your Planting Window? What Can You Still Grow?

If you're starting later in the season, use this normals-based guide to what typically still has time to mature in Casper at a few common planting checkpoints. We apply a 15% safety margin to separate crops that usually fit from ones that are more borderline.

Usually fits Borderline Too tight

Crop	Heat Units	May 15	Jun 1	Jul 1	Aug 1
Spinach	450 (base 40)	✅	✅	✅	✅
Lettuce	500 (base 40)	✅	✅	✅	✅
Pea	600 (base 40)	✅	✅	✅	✅
Beet	650 (base 40)	✅	✅	✅	✅
Kale	700 (base 40)	✅	✅	✅	✅
Zucchini	750 (base 50)	✅	✅	✅	⚠️
Carrot	750 (base 40)	✅	✅	✅	✅
Swiss chard	750 (base 40)	✅	✅	✅	✅
Cucumber	800 (base 50)	✅	✅	✅	⚠️
Broccoli	900 (base 40)	✅	✅	✅	✅
Bean	900 (base 50)	✅	✅	✅	❌
Cabbage	1000 (base 40)	✅	✅	✅	✅
Cauliflower	1000 (base 40)	✅	✅	✅	✅
Sweet corn	1100 (base 50)	✅	✅	✅	❌
Potato	1100 (base 45)	✅	✅	✅	⚠️
Tomato	1200 (base 50)	✅	✅	✅	❌
Pepper	1300 (base 50)	✅	✅	⚠️	❌
Onion	1300 (base 45)	✅	✅	✅	❌
Winter squash	1300 (base 50)	✅	✅	⚠️	❌
Pumpkin	1300 (base 50)	✅	✅	⚠️	❌

Climate normals GDD planning

Compare your season’s typical heat accumulation against crop requirements before first fall frost.

Heat matters more than calendar days Use this when crop maturity depends on warmth, not just frost-free days. Especially useful for warm-season crops and short-season locations.

Best for borderline crops Especially useful for warm-season crops and short-season locations.

Check Crop Maturity and Timing in Casper

Enter a ZIP / Postal Code in Casper and your planting date to see whether different crops can typically mature before first fall frost.

ZIP / Postal

Crops

Select one or more crops.

Select Outdoor sow / Transplant date

How the Growing Season Works in Casper

Casper is mostly a timing-and-variety season. Reliable results usually come from planting on time, matching maturity to the frost window, and making good use of the remaining summer heat.

Start on time: early establishment is often the biggest controllable factor for warm-season success.
Match crops to the window: dependable harvests usually come from realistic maturity timing, not optimistic timing.
Use late summer well: fast greens, roots, and compact crops are often the best fit for a second round.

Late-summer note: there is often still meaningful heat left around early August, so second plantings of faster crops can still be worthwhile.

Remaining Season Heat in Casper (Base 50 GDD)

Growing Degree Days (Base 50°F) measure heat accumulation. “Remaining GDD” shows how much usable heat is typically still available from a given date onward in a normal season.

Planting date	Base	Typical GDD still available
May 15	50	1968
June 1	50	1888
July 1	50	1513
August 1	50	862

Use these values to judge whether a crop or variety still has enough heat left after planting. This is especially helpful for later sowings, shorter-maturity choices, and deciding whether a second round is realistic.

Typical Season Rhythm

A practical “typical year” rhythm for planning. Use it as a baseline, then adjust for microclimates and variety maturity.

Stage	What it usually means
Early season	Start cold-tolerant crops, prep beds, and pay more attention to soil warmth and night temperatures than to the calendar alone.
Main planting	Around May 26, the main planting push usually begins as frost risk fades. Warm-season crops generally perform best when they get established promptly.
Peak growth	This is when water, fertility, spacing, and pest pressure have the biggest effect on final yield.
Late-summer decisions	There is often enough late-season heat left for a meaningful second round of quick crops.
Finish window	Plan to have frost-sensitive crops mostly wrapped up by September 22. Cooling nights often slow crops before the first real frost arrives.

Typical season length: 119 frost-free days between the median spring and fall frost dates.

How Growing Conditions Vary Across Casper

Growing conditions often vary more within Casper than most gardeners expect. Differences in elevation, exposure, cold-air drainage, and nearby pavement or buildings can shift frost timing and change how much usable season you really have.

Most areas behave somewhat similarly, though small site differences still affect frost timing and spring warmup.
Urban areas, walls, and sheltered gardens usually stay warmer than open rural or wind-exposed sites.
Cold air settles in low spots, so slightly elevated beds often avoid the earliest frosts.
South- and west-facing areas usually warm sooner in spring and can stay productive later into fall.

How Gardeners Adapt

Experienced gardeners in Casper usually adjust their timing and crop choices to match how the season actually behaves, not just the calendar.

Planting warm-season crops promptly once frost risk fades.
Using row cover or low tunnels to smooth out temperature swings early and late in the season.
Succession planting fast crops to keep beds productive through summer.
Watching local conditions closely and adjusting timing year by year.

Common Timing Mistakes

These patterns show up again and again in Casper — especially in typical years.

Waiting too long after last frost to plant warm-season crops, which compresses harvest timing.
Relying on calendar dates instead of crop maturity and typical frost timing.