USDA zone 5a in Montana
USDA plant hardiness zone 5a covers 47 locations across Montana (average annual extreme minimum −20 to −15 °F): Absarokee, MT, Anaconda-Deer Lodge County, MT, Basin, MT, Bearcreek, MT, Biddle, MT, Big Sky, MT, and 41 more. Average last spring frost across this group ranges April 30 (McAllister) to June 16 (Jeffers), and growing seasons run 78–162 days (Jeffers to McAllister) — even within one state, because hardiness sets winter survival, not planting dates. The table below gives every Montana location's own frost dates; the printable planting calendar uses Bozeman, this group's median-season location.
- USDA zone
- 5a−20 to −15 °F
- Last frost range
- Apr 30–Jun 16avg, 32°F
- First frost range
- Sep 2–Oct 10avg, 32°F
- Growing season range
- 78–162days
Locations in this group
Every location below shares this zone and a nearby weather station, but keeps its own frost dates — find your town for its own numbers, or use the ZIP planner on the home page for an instant personalized answer.
| Location | Also covers | Nearest station | Last frost | First frost | Season (days) |
|---|---|---|---|---|---|
| Absarokee | Nye | Nye #2 | Jun 1 | Sep 11 | 100 |
| Anaconda-Deer Lodge County | Maxville, Philipsburg | Anaconda | Jun 1 | Sep 14 | 105 |
| Basin | Boulder | Boulder | Jun 7 | Sep 8 | 90 |
| Bearcreek | — | Red Lodge | Jun 3 | Sep 19 | 106 |
| Biddle | — | Biddle 8 Sw | May 14 | Sep 28 | 134 |
| Big Sky | South Glastonbury | Gardiner | May 21 | Sep 27 | 128 |
| Big Timber | Greycliff | Big Timber | May 14 | Sep 26 | 133 |
| Billings | Lockwood, Laurel, Mountain View Colony | Billings Logan Intl Ap | May 4 | Oct 7 | 156 |
| Birney | — | Sonnette 7 Sw | May 25 | Sep 19 | 115 |
| Bozeman * | — | Bozeman Montana State Univ | May 26 | Sep 22 | 116 |
| Butte-Silver Bow | Whitehall | Butte Bert Mooney Ap | Jun 13 | Sep 5 | 83 |
| Butte-Silver Bow | Glen | Divide | Jun 10 | Sep 7 | 85 |
| Clyde Park | Springdale | Livingston Mission Fld | May 27 | Sep 14 | 108 |
| Colstrip | — | Colstrip | May 15 | Sep 30 | 138 |
| Columbia Falls | Essex | Hungry Horse Dam | May 9 | Oct 1 | 141 |
| Columbus | Reed Point | Columbus | May 27 | Sep 14 | 108 |
| Condon | Seeley Lake | Lindbergh Lake | May 20 | Sep 22 | 120 |
| Coram | Polebridge | W Glacier | May 18 | Sep 20 | 124 |
| Forty Mile Colony | — | Wyola 1 Sw | May 21 | Sep 17 | 117 |
| Four Corners | — | Bozeman 6 W Exp Farm | May 23 | Sep 23 | 123 |
| Hebgen Lake Estates | — | Hebgen Dam | Jun 15 | Sep 10 | 87 |
| Helmville | — | Elliston | Jun 9 | Sep 8 | 91 |
| Indian Springs | — | Eureka Rs | May 11 | Sep 27 | 138 |
| Jackson | — | Salmon-ksra | May 17 | Sep 24 | 127 |
| Jeffers | — | Ennis | Jun 16 | Sep 4 | 78 |
| Lima | Dell, Leadore | Lima | Jun 11 | Sep 10 | 89 |
| Lockwood | — | Billings Wtp | May 10 | Oct 1 | 142 |
| Luther | Nye, Roscoe | Mystic Lake | Jun 5 | Sep 14 | 99 |
| Maverick Mountain | Grant | Dillon U Of Montana Western | Jun 5 | Sep 13 | 98 |
| McAllister | Pony, Norris | Norris Madison Pwr House | Apr 30 | Oct 10 | 162 |
| Muddy | Busby | Busby | May 23 | Sep 15 | 113 |
| Pryor | — | Bridger 2 N | May 14 | Sep 24 | 129 |
| Roberts | Park, Edgar, Fromberg, Boyd, Joliet | Joliet | May 29 | Sep 15 | 107 |
| Snowslip | — | E Glacier | Jun 8 | Sep 5 | 88 |
| South Glastonbury | Pine Creek | Livingston 12 S | May 19 | Sep 25 | 125 |
| Spokane Creek | Helena | Helena Rgnl Ap | May 9 | Sep 30 | 142 |
| Springhill | Amsterdam | Bozeman Gallatin Fld | May 26 | Sep 16 | 112 |
| St. Xavier | Fort Smith | Yellowtail Dam | May 7 | Oct 5 | 151 |
| Sula | — | Darby | May 24 | Sep 23 | 118 |
| Trego | Fortine, Olney, Stryker | Fortine 1 N | May 16 | Sep 18 | 121 |
| Twin Bridges | Silver Star, Mammoth | Twin Bridges | Jun 8 | Sep 2 | 82 |
| Virginia | — | Alder 17 S | Jun 6 | Sep 14 | 98 |
| Virginia | Brandon | Virginia City | Jun 4 | Sep 18 | 106 |
| Wheatland | Willow Creek, Cardwell | Trident | May 9 | Sep 27 | 139 |
| Whitefish | — | Whitefish | May 16 | Sep 25 | 129 |
| Winston | Radersburg | Townsend 3se | May 19 | Sep 19 | 122 |
| Wisdom | — | Gibbonsville #2 | Jun 1 | Sep 17 | 107 |
* Bozeman is this group's median-season location — the calendar below is computed from its data.
Data: NOAA NCEI U.S. Climate Normals 1991–2020 (public domain) and USDA Plant Hardiness Zone Map 2023. Planting windows synthesized from U.S. Cooperative Extension guides.
Planting calendar (Bozeman, representative)
Computed from Bozeman's average frost dates — the median-season location in this Montanazone 5a group. hatched = start seeds indoors, solid green = plant out, teal = a fall sowing, and the terracotta dot marks the estimated first harvest. Ranges are extension-guide planning guidance, not guarantees — your own location's dates may run a week or two earlier or later (see the table above).
- Start indoors
- Plant out
- Fall sowing
- First harvest
| Crop | Frost tolerance | Start indoors | Plant out | First harvest | Fall planting | Season fit |
|---|---|---|---|---|---|---|
| Tomato | Tender | Mar 31 – Apr 14 | Jun 2 – Jun 9 | Aug 1 – Aug 21 | — | matures comfortably |
| Pepper | Very tender | Mar 17 – Mar 31 | Jun 9 – Jun 16 | Aug 8 – Sep 7 | — | matures comfortably |
| Cucumber | Tender | Apr 28 – May 5 | Jun 2 – Jun 9 | Jul 22 – Aug 11 | — | matures comfortably |
| Summer squash / zucchini | Tender | — | Jun 2 – Jun 9 | Jul 17 – Aug 1 | — | matures comfortably |
| Bush bean | Tender | — | Jun 2 – Jun 9 | Jul 22 – Aug 1 | Jul 24 – Aug 3 | matures comfortably |
| Sweet corn | Tender | — | May 26 – Jun 9 | Jul 25 – Aug 24 | — | matures comfortably |
| Basil | Very tender | Apr 14 – Apr 28 | Jun 2 – Jun 9 | Jul 2 – Jul 17 | — | matures comfortably |
| Lettuce | Half-hardy | Apr 14 – Apr 28 | Apr 28 – May 12 | Jun 12 – Jun 27 | Jul 10 – Jul 25 | matures comfortably |
| Pea | Hardy | — | Apr 14 – Apr 28 | Jun 8 – Jun 23 | Jun 30 – Jul 15 | matures comfortably |
| Spinach | Hardy | — | Apr 14 – Apr 28 | May 24 – Jun 3 | Jul 20 – Jul 30 | matures comfortably |
| Carrot | Half-hardy | — | May 5 – May 12 | Jul 4 – Jul 24 | Jun 20 – Jul 10 | matures comfortably |
| Broccoli | Half-hardy | Mar 31 – Apr 14 | Apr 28 – May 12 | Jun 22 – Jul 12 | Jun 25 – Jul 15 | matures comfortably |
Which crops fit this growing season
Using Bozeman's own 116-day growing season (32°F, NOAA 1991–2020 median) against each crop's real days-to-maturity range: 12 of 12 crops mature here with comfortable margin. A different location in the table above with a longer or shorter season will get a different mix — the ZIP planner on the home page gives your own.
Frost & freeze dates (Bozeman)
From NOAA's 1991–2020 Climate Normals at station USC00241044. The median (p50) is the average date; the 90%-safe column is the date the freeze has passed in about 9 years out of 10 — the conservative date to plant after or harvest before.
| Threshold | Last spring — avg | Last spring — 90%-safe | First fall — avg | First fall — 90%-safe | Season (days) |
|---|---|---|---|---|---|
| 36°F | Jun 14 | Jun 28 | Sep 8 | Sep 23 | 87 |
| 32°F (freeze) | May 26 | Jun 14 | Sep 22 | Oct 5 | 116 |
| 28°F | May 8 | May 26 | Oct 3 | Oct 19 | 147 |
| 24°F | Apr 25 | May 11 | Oct 13 | Oct 30 | 170 |
Growing degree days
Growing degree days (GDD) accumulate warmth above a base temperature over the year — a better predictor of crop development than the calendar alone. This group's median GDD (base 50°F) across all 47 locations is 1,719; Bozeman's own reading is shown below.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 1,719 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 3,511 | cool-season crops (brassicas, greens) |
Hardiness zone 5a in Montana
Zone 5a means an average annual extreme minimum winter temperature of about −20 to −15 °F on the USDA's 2023 map — the number that tells you which perennials, shrubs, and trees reliably survive an average winter here. It does not set your planting dates, which come from the frost calendar above. Montana spans 7 hardiness zones in this dataset — see all Montana locations for the full range, including zones3b, 4a, 4b, 5b, 6a, 6b.
Explore zone 5a in other states at zone 5a, or see all USDA hardiness zones.
Frequently asked questions
- What does USDA hardiness zone 5a mean in Montana?
- Zone 5a means an average annual extreme minimum winter temperature of −20 to −15 °F — the standard USDA measure of which perennials survive winter. 47 locations in Montana fall in this zone. It does not set planting dates; see the frost calendar below for that.
- Where in Montana's zone 5a is the growing season longest?
- McAllister runs the longest season on this page at about 162 days; Jeffers is shortest at about 78 days — they share the same hardiness zone, but they sit at different weather stations, so their frost calendars differ.
- When should I plant tomatoes in Montana's zone 5a?
- Using Bozeman's frost dates (this page's median-season location): start seeds indoors about Mar 31 – Apr 14, then transplant outside about Jun 2 – Jun 9. Your own location in the table above may differ by a week or two — use the ZIP planner on the home page for your exact station's dates.
- Does every location in Montana's zone 5a have the same frost dates?
- No — they do not all share a weather station, so frost dates vary by a week or more across the 47 locations listed (see the table above for each location's own dates).
Sources & method
Frost, freeze, growing-season, and growing-degree-day figures are NOAA NCEI U.S. Climate Normals 1991–2020, one reading per location's own nearest station (see the table above). The hardiness zone is the USDA Plant Hardiness Zone Map 2023, matched to each location's ZIP. Planting windows are computed by counting from the average last and first frost using per-crop offsets synthesized from U.S. Cooperative Extension guides — the full method and citations are on the methodology page.