When is the last frost in Casper, WY?

The average last spring frost (50% probability of 32°F) in Casper is around May 26, based on NOAA/NCEI 1991–2020 normals at the Casper Natrona Co Ap, WY station (13.4 mi away). Half of years it falls outside that date, so wait 1–2 weeks past it before setting out frost-tender plants.

When is the first fall frost in Casper?

The average first fall frost in Casper, WY is around September 22, giving roughly a 117-day frost-free growing season.

What planting zone is Casper, WY?

Casper is in USDA plant hardiness zone 5a (average annual extreme minimum temperature -20 to -15°F), from the 2023 USDA Plant Hardiness Zone Map.

What is the weather like in Casper?

In Casper, WY the warmest month is July (avg high 89°F) and the coldest is December (avg low 14.8°F). It averages about 12.2″ of precipitation a year and 71.8″ of snow.

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Casper, WY Planting Calendar & Frost Dates

USDA hardiness zone 5a · ZIP 82601 · elevation 1627′ · NOAA & USDA data

Casper is in USDA hardiness zone 5a (winters can dip to -20 to -15°F), with a growing season of about 117 days between the average last spring frost (May 26) and first fall frost (September 22). The warmest month is July (avg high 89°F); the coldest is December (avg low 14.8°F). It averages 12.2″ of precipitation a year and 71.8″ of snow, mostly mid-winter. Start cool-season crops several weeks before the last frost; wait until after it for tomatoes, peppers and other tender crops.

Hardiness zone

min temp -20 to -15°F

Last spring frost

May 26

avg (50% prob, 32°F)

First fall frost

September 22

avg (50% prob, 32°F)

Growing season

117 days

frost-free window

Warmest month

July

avg high 89°F

Month-by-month typical weather in Casper

Average conditions from the NOAA/NCEI 1991–2020 U.S. Climate Normals at Casper Natrona Co Ap, WY (13.4 mi away). Temperatures °F, precipitation & snow in inches.

Month	Avg high	Avg low	Mean	Precip (in)	Snow (in)
January	35.2	15	25.1	0.5	9
February	37.8	15.4	26.6	0.6	10.9
March	48.8	22.7	35.8	0.8	10.3
April	56.3	28.2	42.3	1.4	10.5
May	66.8	37.1	52	2.2	2.6
June	79.6	45.4	62.5	1.3	0.1
July	89	53	71	1.2	0
August	86.7	51.4	69	0.8	0
September	75.6	42.2	58.9	1	1.5
October	59.7	30.9	45.3	1.2	7
November	45.9	22	34	0.6	8.9
December	34.7	14.8	24.8	0.6	11

What to plant when in Casper

Crop	Season	What to do & when
Tomatoes	warm	Start seeds indoors: April 14 · Transplant out: June 2
Peppers	warm	Start seeds indoors: March 31 · Transplant out: June 9
Cucumbers	warm	Direct sow: June 2
Zucchini / squash	warm	Direct sow: June 2
Bush beans	warm	Direct sow: June 2
Sweet corn	warm	Direct sow: June 2
Basil	warm	Transplant out: June 2
Peas	cool	Sow (spring): April 21 · Sow (fall): July 28
Spinach	cool	Sow (spring): April 14 · Sow (fall): July 28
Lettuce	cool	Sow (spring): April 28 · Sow (fall): July 28
Kale	cool	Transplant (spring): May 5 · Sow (fall): July 14
Broccoli	cool	Transplant (spring): May 12
Carrots	cool	Sow (spring): May 5 · Sow (fall): July 14
Onions	cool	Transplant (spring): April 28
Potatoes	cool	Plant seed potatoes: May 12
Radishes	cool	Sow (spring): April 28 · Sow (fall): August 11

Dates are computed from Casper's average frost dates using standard cool-/warm-season timing. They're a starting point — a cold spring, a warm microclimate, or a fast-maturing variety can shift them by a week or two.

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Gear that helps you plant on time

Some links below are Amazon affiliate links (tag theboringthin-20). If you buy through them we may earn a small commission at no extra cost to you — it keeps this almanac free. We only list generic, genuinely-useful categories.

Soil thermometer →Know when the ground is warm enough to sow — the honest signal, not the calendar.Seed-starting trays + dome →Start tomatoes & peppers indoors on the schedule below.Seedling heat mat →Warms the soil for faster, more even germination indoors.Floating row cover / frost cloth →Buys you 4–8°F to beat an early or late frost.Raised garden bed kit →Warms and drains faster in spring than in-ground soil.Garden gloves →Basic kit for transplant day.

Nearby cities in Wyoming

Cheyenne, WY

Sources & method. Hardiness zone: 2023 USDA Plant Hardiness Zone Map (PRISM Climate Group, Oregon State University). Frost dates & growing season: NOAA/NCEI 1991–2020 U.S. Climate Normals, nearest station with published freeze normals — Casper Natrona Co Ap, WY, 13.4 mi (confidence: medium). Monthly weather normals: Casper Natrona Co Ap, WY, 13.4 mi (confidence: medium). ZIP centroid from U.S. Census 2023 ZCTA data. Frost dates are the 50%-probability date — half of years frost occurs outside the stated date. Nothing here is invented; where the nearest station is far, we say so. Last updated 2026-07-22.