USDA zone 4a in Montana
USDA plant hardiness zone 4a covers 43 locations across Montana (average annual extreme minimum −30 to −25 °F): Bainville, MT, Brady, MT, Brockway, MT, Brockway, MT, Camrose Colony, MT, Carter, MT, and 37 more. Average last spring frost across this group ranges May 3 (Glasgow) to June 8 (South Browning), and growing seasons run 88–153 days (South Browning to West Glendive) — 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 Fallon, this group's median-season location.
- USDA zone
- 4a−30 to −25 °F
- Last frost range
- May 3–Jun 8avg, 32°F
- First frost range
- Sep 5–Oct 4avg, 32°F
- Growing season range
- 88–153days
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) |
|---|---|---|---|---|---|
| Bainville | Culbertson, Brockton, Froid | Culbertson | May 21 | Sep 20 | 120 |
| Brady | Conrad | Conrad | May 20 | Sep 19 | 119 |
| Brockway | — | Brockway 3 Wsw | May 20 | Sep 19 | 121 |
| Brockway | Jordan | Cohagen | May 25 | Sep 14 | 110 |
| Camrose Colony | — | Tiber Dam | May 16 | Sep 23 | 129 |
| Carter | Dutton | Carter 14 W | May 23 | Sep 23 | 120 |
| Chester | — | Chester | May 24 | Sep 17 | 115 |
| Circle | — | Circle | May 17 | Sep 22 | 126 |
| Crane | Savage, Bloomfield | Savage | May 12 | Sep 25 | 135 |
| Eagle Creek Colony | Whitlash | Dunkirk 19nne | May 23 | Sep 14 | 112 |
| Fallon * | — | Mildred 5 N | May 20 | Sep 22 | 124 |
| Flaxville | — | Bredette | May 20 | Sep 21 | 122 |
| Fort Belknap Agency | — | Harlem | May 16 | Sep 21 | 125 |
| Fort Benton | — | Ft Benton | May 15 | Sep 22 | 129 |
| Fox Lake | Crane, Fairview, East Fairview | Sidney | May 11 | Sep 27 | 137 |
| Frazer | Wolf Point | Wolf Point Intl Ap | May 16 | Sep 20 | 125 |
| Frazer | — | Ft Peck Pwr Plt | May 8 | Oct 1 | 145 |
| Glasgow | — | Glasgow #2 | May 3 | Oct 1 | 151 |
| Hinsdale | — | Hinsdale 4 Sw | May 15 | Sep 26 | 132 |
| Hogeland | Turner | Turner 11n | May 19 | Sep 21 | 124 |
| Inverness | Sage Creek Colony | Joplin | May 21 | Sep 19 | 119 |
| Ismay | — | Mizpah 4 Nnw | May 22 | Sep 15 | 117 |
| Jordan | — | Jordan Ap | May 18 | Sep 20 | 123 |
| Kremlin | Hingham | Gildford | May 24 | Sep 15 | 114 |
| Lodge Pole | — | Zortman | May 18 | Sep 23 | 126 |
| Loma | — | Loma | May 20 | Sep 19 | 120 |
| Malta | — | Malta 35 S | May 16 | Sep 23 | 128 |
| Plentywood | — | Raymond Border Stn | May 19 | Sep 23 | 125 |
| Plevna | — | Plevna | May 21 | Sep 20 | 121 |
| Poplar | — | Wolf Point 29 Ene | May 24 | Sep 14 | 110 |
| Richey | Vida | Vida 6 Ne | May 16 | Sep 22 | 129 |
| Rocky Boy West | Big Sandy | Big Sandy | May 17 | Sep 25 | 128 |
| Seville Colony | — | Cut Bank Muni Ap | May 24 | Sep 15 | 113 |
| Shelby | Kevin | Shelby | May 23 | Sep 16 | 115 |
| Silver Gate | — | Mystic Lake | Jun 5 | Sep 14 | 99 |
| South Browning | — | E Glacier | Jun 8 | Sep 5 | 88 |
| St. Marie | Nashua | St Marie | May 13 | Sep 27 | 134 |
| Sunburst | Whitlash | Sunburst 8 E | May 17 | Sep 25 | 129 |
| Terry | Rosebud | Miles City F Wiley Fld | May 8 | Sep 30 | 144 |
| Terry | — | Terry | May 12 | Sep 28 | 137 |
| Ulm | Vaughn, Cascade Colony | Sun Rvr 4 S | Jun 2 | Sep 10 | 96 |
| West Glendive | — | Glendive | May 3 | Oct 4 | 153 |
| Wibaux | — | Wibaux 2 E | May 27 | Sep 16 | 112 |
* Fallon 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 (Fallon, representative)
Computed from Fallon's average frost dates — the median-season location in this Montanazone 4a 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 25 – Apr 8 | May 27 – Jun 3 | Jul 26 – Aug 15 | — | matures comfortably |
| Pepper | Very tender | Mar 11 – Mar 25 | Jun 3 – Jun 10 | Aug 2 – Sep 1 | — | matures comfortably |
| Cucumber | Tender | Apr 22 – Apr 29 | May 27 – Jun 3 | Jul 16 – Aug 5 | — | matures comfortably |
| Summer squash / zucchini | Tender | — | May 27 – Jun 3 | Jul 11 – Jul 26 | — | matures comfortably |
| Bush bean | Tender | — | May 27 – Jun 3 | Jul 16 – Jul 26 | Jul 24 – Aug 3 | matures comfortably |
| Sweet corn | Tender | — | May 20 – Jun 3 | Jul 19 – Aug 18 | — | matures comfortably |
| Basil | Very tender | Apr 8 – Apr 22 | May 27 – Jun 3 | Jun 26 – Jul 11 | — | matures comfortably |
| Lettuce | Half-hardy | Apr 8 – Apr 22 | Apr 22 – May 6 | Jun 6 – Jun 21 | Jul 10 – Jul 25 | matures comfortably |
| Pea | Hardy | — | Apr 8 – Apr 22 | Jun 2 – Jun 17 | Jun 30 – Jul 15 | matures comfortably |
| Spinach | Hardy | — | Apr 8 – Apr 22 | May 18 – May 28 | Jul 20 – Jul 30 | matures comfortably |
| Carrot | Half-hardy | — | Apr 29 – May 6 | Jun 28 – Jul 18 | Jun 20 – Jul 10 | matures comfortably |
| Broccoli | Half-hardy | Mar 25 – Apr 8 | Apr 22 – May 6 | Jun 16 – Jul 6 | Jun 25 – Jul 15 | matures comfortably |
Which crops fit this growing season
Using Fallon's own 124-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 (Fallon)
From NOAA's 1991–2020 Climate Normals at station USC00245668. 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 | May 29 | Jun 16 | Sep 12 | Sep 26 | 103 |
| 32°F (freeze) | May 20 | Jun 2 | Sep 22 | Oct 6 | 124 |
| 28°F | May 7 | May 23 | Oct 1 | Oct 16 | 145 |
| 24°F | Apr 28 | May 13 | Oct 12 | Oct 27 | 166 |
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 43 locations is 2,118; Fallon's own reading is shown below.
| Model | °F·days | Used for |
|---|---|---|
| Base 50°F (warm-season) | 2,279 | standard warm-season base (tomato, corn, beans) |
| Base 40°F (cool-season) | 4,125 | cool-season crops (brassicas, greens) |
Hardiness zone 4a in Montana
Zone 4a means an average annual extreme minimum winter temperature of about −30 to −25 °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, 4b, 5a, 5b, 6a, 6b.
Explore zone 4a in other states at zone 4a, or see all USDA hardiness zones.
Frequently asked questions
- What does USDA hardiness zone 4a mean in Montana?
- Zone 4a means an average annual extreme minimum winter temperature of −30 to −25 °F — the standard USDA measure of which perennials survive winter. 43 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 4a is the growing season longest?
- West Glendive runs the longest season on this page at about 153 days; South Browning is shortest at about 88 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 4a?
- Using Fallon's frost dates (this page's median-season location): start seeds indoors about Mar 25 – Apr 8, then transplant outside about May 27 – Jun 3. 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 4a 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 43 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.