Montana’s growing zones range from 3a to 6b. The coldest areas are along the eastern and central Canadian border and the warmest are in the northeast.
The growing zones, also called hardiness zones or planting zones, help gardeners and growers determine which plants are best suited for their location. Most of Montana’s prominent towns and cities are in 4b to 5b, including Helena, Kalispell, Billings, Bozeman, Great Falls, and Missoula.
An overview
Montana’s growing zones, also called planting zones or hardiness zones, range from 3a to 6b. 3a is in small pockets near Coment Mountain and the south central Rockies, and 6b is in the northeast, primarily in Sanders County and parts of Lincoln County.
The USDA explains, “The Plant Hardiness Zone Map (PHZM) is based on the average annual extreme minimum winter temperature, displayed as 10-degree F zones ranging from zone 1 (coldest) to zone 13 (warmest).” Each zone is divided into half zones designated as ‘a’ (colder) and ‘b’ (warmer) and there is a 5-degree difference between the two.
With a state as big as Montana, it’s not a surprise that there are so many hardiness zones. Here are several prominent cities in The Treasure State and their hardiness zones.
- Helena: 4b
- Kalispell: 5b
- Billings: 5a
- Bozeman: 5a
- Great Falls: 4b
- Missoula: 5b
“All Plant Hardiness Zone Maps (PHZM) should serve as general guides for growing perennial plants,” according to the USDA. Below, we’ve included some perennials suited for each hardiness zone, but many of these plants are suitable for multiple regions. For more information, check out Montana Native Plants for Your Landscape.
Zone 3
Zone 3 in Montana is along the north-central and northeastern Canadian border and in small pockets in the southwest near the southern Idaho border. The majority of Montana’s zone 3 is 3b, but a few of the pockets also contain 3a
Average low temperature: 3a is -40 to -35; 3b is -35 to -30
Average first frost: September 8 to 15
Average last frost: May 1 to 16
Zone 3 plant types: Choose plants that are cold-hardy and can handle harsh winter temperatures and a shorter growing season. Try starting seeds and bulbs indoors.
Zone 3 perennials: Asters, crocus, hydrangeas, phlox, sedum
Zone 4
In Montana, Zone 4 covers much of the state. Zone 4a borders northern zone 3 and goes as far west as Glacier County. It covers much of the northeastern part of the state, too. Zone 4b includes southeast and central Montana and goes as far west as Pondera and Tetor counties. It also includes pockets in southwestern Montana.
Average low temperature: 4a is -30 to -25; 4b is -25 to -20
Average first frost: September 21 to October 7
Average last frost: April 24 to May 12
Zone 4 plant types: Select plants that are cold-hardy and can handle frigid winter temperatures and a shorter growing season. Starting seeds and bulbs indoors can increase bloom time.
Zone 4 perennials: Bee balm, cannas, coneflower, delphiniums, hibiscus
Zone 5
Zone 5 in Montana covers the central border and most of the southwest. Zone 5 also includes a strip in the northwest between zone 4 and zone 6 as well as a few pockets in central and southeastern parts of the state. Zone 5a is primarily in the southern and southwestern area and zone 5b is mostly in the northwest.
Average low temperature: 5a is -20 to -15. 5b is -15 to -10
Average first frost: October 13 to 21
Average last frost: April 7 to 30
Zone 5 plant types: Choose cold-hardy plants that can handle the cold winter temperatures and a shorter growing season. For a more fruitful growing season, plant seeds and bulbs indoors.
Zone 5 perennials: Begonias, dahlias, gladiolus, lilies, roses
Zone 6
In Montana, zone 6 is in the northwest, on the western side of the continental divide. It includes most of Sanders and Mineral counties, parts of Lake, Flathead, and Lincoln counties, and small sections of Missoula, Ravalli, and Granite counties.
Average low temperature: 6a is -10 to -5; 6b is -5 to 0
Average first frost: October 17 to 31
Average last frost: April 1 to 21
Zone 6 plant types: Select cold-hardy plants that can survive chilly winter temperatures and a shorter growing season. Start seeds and bulbs indoors, so you can sow already thriving plants after the last frost.
Zone 6 perennials: Hyacinths, yarrow, daffodils, hostas, peonies
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