Planting calendars

Wyoming and Montana planting calendar

Spring freeze probabilities for Cheyenne, Laramie, Casper, and Jackson, plus Montana station medians from Billings to Butte.

By the Thin Air Harvest editorial team. Updated November 1, 2026.

Wyoming and Montana share a high-plains climate and a mountain climate, often in the same county. A Billings vegetable garden and a Butte vegetable garden should not share a weekend. This calendar keeps them apart and uses published station tables only. Spring dates for Wyoming come from the University of Wyoming Extension freeze-probability table used in its Barnyards and Backyards resources.

Fall dates are quoted only for Cheyenne and Laramie, from the National Weather Service, because that is a different record and this site will not subtract one from the other to invent a season length. Montana dates come from the freeze-occurrence table hosted by Montana State University Extension.

How to read a median and a 1-in-10 late date is covered in reading a spring frost. The Wyoming and Montana tables use the same three-column idea.

Wyoming spring, 32°F

Jackson’s July median is a short, cold season. Treat it like the Colorado mountain-town calendar, not like Cheyenne. Laramie’s June 7 median is a full month later than Cheyenne’s May 12. They are two hours apart and they are not the same garden.

National Weather Service fall statistics for a long record, 1951–2025, as published for the Cheyenne office: Cheyenne’s median first fall 32°F freeze is September 29, with a 10 percent chance by September 13 and a 90 percent chance by October 15.

Laramie’s median first fall 32°F is September 13, with a 10 percent chance by August 31 and a 90 percent chance by September 23. Those are fall medians from a newer, longer record than the spring table. Use them as fall guidance. Do not subtract them from the spring medians and call the result official.

Montana spring, 32°F

Bozeman’s campus median is May 26. The Belgrade airport and the west experimental farm sit at June 4. People who live between them should not pick the date they prefer.

Pick the station that sits like their land, or keep a thermometer and use the later date until the yard has a record. Butte’s June 20 median is a mountain problem.

Miles City’s May 6 median is a plains problem. The high-plains plant page matches the plains. The mountain crop list matches Butte, Jackson, and the high side of Bozeman.

April

On the plains, April is soil-prep and hardy-seed month only when the ground crumbles and your median is still weeks away. Cheyenne’s median of May 12 means a careful pea and spinach sowing can start in the second half of April if the soil is workable, with cover ready.

Billings, with a May 4 median, is similar to a Front Range city and can follow that city’s hardy-crop timing. Laramie, Jackson, and Butte should not plant in April except under a cold frame for greens. Start indoor seed so it is ready for a late May or June set-out, not so it is root-bound in a window for two months.

May

Cheyenne, Billings, Miles City, Helena, and Great Falls: May is the main planting month. Hardy crops early, if they are not already in. Tender crops around the median if you can cover them.

Very tender crops after the late bound, or under cover. Cheyenne’s late bound is May 26. Billings’ is May 17. Planting tomatoes on May 1 in either town is early.

Bozeman campus can take hardy sowings in May. Belgrade and the west side should treat May as a cautious month and put the main tender plantings into early June.

Missoula’s median of May 23 at the 2 NE station supports a late-May tender planting with cover, not an early-May one. The airport can differ. This page does not quote a garbled airport row. Use 2 NE or your own gauge.

June

Laramie, Jackson, Butte, and the colder Bozeman sites do their real planting in June.

Potatoes two to three weeks before the median.

Peas, greens, and brassicas as the soil warms. Tomatoes only if short-season and covered, and only if the days-to-maturity sum fits before the fall risk you can document.

Jackson’s July 10 median means much of June is still early. A 50-day bean after a July 10 median can still finish if September is kind. A pepper is a wager.

Plains gardens in June are watering, weeding, and covering for hail and wind. Both are normal. The wind and hail pages are the structures.

July and August

Plains: harvest and a fall sowing of brassicas or carrots if your fall median is late September or better. Cheyenne’s NWS median first freeze of September 29 allows a modest fall crop. Laramie’s September 13 median does not leave much room. Sow fall crops in Laramie only if they mature fast.

Mountains: July is the growing month, not a second planting month, except for radishes and lettuce. Watch for an early frost in August at high stations. Have a cover on the salad bed. Do not expect winter squash.

September and October

Use the NWS fall medians where you have them and the forecast everywhere else. Harvest, pull the drip lines before a hard freeze, and plant garlic as soon as the soil is cool and still workable.

In Jackson and Butte that may be September. In Billings it may be October. Mulch garlic after the surface freezes. Clean up diseased vines.

Water trees on a mild day if autumn has been dry. Chinook winds will dry them further. The fruit-bud page is why a January thaw is not only a vegetable problem.

Winter

This is wind-and-vole season. Hardware cloth on trunks, mulch pulled off the bark, fences checked. Order seed that fit last year’s notes. Drop the crop that needed a September that Laramie or Butte did not have.

Checklist

• Separate plains stations from Laramie, Jackson, and Butte.
• Use Bozeman campus and Belgrade as different dates.
• Do not invent a frost-free day count by subtracting mismatched tables.
• Plant hardy crops before the median when soil allows. Hold tender crops if you cannot cover them.
• Put high stations on the mountain crop list.
• Record your own last and first 32°F mornings.

Sources

• University of Wyoming Extension, Barnyards and Backyards spring freeze probability table.
• National Weather Service, Cheyenne office, fall first freeze statistics.
• Montana State University Extension, Frost Freeze Data for Montana.
• MSU Extension Master Gardener, frost data page.