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Frost Dates and Planting Windows in Montana

The 32°F frost dates at the 216 weather stations in Montana with NOAA's 1991–2020 Climate Normals, and the planting windows they give. These are long-term statistics, not a forecast. For the dates at the station nearest you, enter your ZIP code.

The planner uses the weather station nearest your ZIP code.

Frost dates across Montana

Each risk level uses a date with a set chance of frost. In spring, it's the chance of a 32°F frost on or after the last-frost date. In fall, it's the chance of the first 32°F frost on or before the first-frost date. At the Typical level (30%), the last frost ranges from May 5 to June 25 across the state, and the first frost from August 27 to October 8.

32°F frost dates: earliest and latest among 216 stations, by risk level
Risk levelEarliest last frostLatest last frostEarliest first frostLatest first frost
Conservative (10%)May 14NORRIS MADISON PWR HOUSE, MT USJuly 8LEWISTOWN 42 WSW, MT USAugust 15OPHEIM 12 SSE, MT USSeptember 30BIGFORK 13 S, MT US
Typical (30%)May 5BIGFORK 13 S, MT USJune 25LEWISTOWN 42 WSW, MT USAugust 27TWIN BRIDGES, MT USOctober 8BIGFORK 13 S, MT US
Aggressive (50%)April 30NORRIS MADISON PWR HOUSE, MT USJune 18TIZER GARDENS, MT USSeptember 22 stationsOctober 15BIGFORK 13 S, MT US

Growing season length

The growing season is the stretch between the last spring frost and the first fall frost at 32°F. NOAA gives it as a length with a chance of being at least that long. Each risk level uses the length with that chance of a shorter season, so Conservative shows the shortest lengths.

Growing season at 32°F: shortest and longest among 216 stations
Risk levelShortestLongest
Conservative (90% chance of at least this long)52 daysLEWISTOWN 42 WSW, MT US144 daysBIGFORK 13 S, MT US
Typical (70% chance of at least this long)67 daysLEWISTOWN 42 WSW, MT US157 daysBIGFORK 13 S, MT US
Aggressive (50% chance of at least this long)77 daysLEWISTOWN 42 WSW, MT US165 daysBIGFORK 13 S, MT US
Number of stations by growing season length, Typical (70% chance of at least this long)
Growing seasonStations
60–79 days14
80–99 days34
100–119 days89
120–139 days67
140–159 days12

Planting windows across Montana

For each crop, the earliest start and the latest end of its Typical windows among the stations. A window at any one station is shorter and falls inside this span. Transplant dates are for seedlings. A fall window is left out at stations where it would start on or before the last day of the spring window, so some rows cover fewer stations.

Typical planting windows (30% frost dates): earliest start and latest end among stations
Crop and taskEarliest startLatest endStations
Basil: Transplant outdoorsMay 19July 9216 of 216
Bean: Sow outdoorsMay 5June 25216 of 216
Beet: Sow outdoorsApril 7June 25216 of 216
Beet: Sow for fallJune 9August 19194 of 216
Broccoli: Transplant outdoorsApril 7June 11216 of 216
Broccoli: Transplant for fallMay 30August 19198 of 216
Brussels sprouts: Transplant outdoorsApril 7June 11216 of 216
Brussels sprouts: Transplant for fallMay 17August 29159 of 216
Cabbage: Transplant outdoorsApril 7June 11216 of 216
Cabbage: Transplant for fallMay 25August 19193 of 216
Cantaloupe: Transplant outdoorsMay 19July 9216 of 216
Cantaloupe: Sow outdoorsMay 19July 9216 of 216
Carrot: Sow outdoorsApril 7June 25216 of 216
Carrot: Sow for fallJune 5August 9175 of 216
Cucumber: Transplant outdoorsMay 12July 2216 of 216
Cucumber: Sow outdoorsMay 5June 25216 of 216
Eggplant: Transplant outdoorsMay 19July 9216 of 216
Garlic: Plant for fallAugust 27October 22216 of 216
Lettuce: Transplant outdoorsApril 7June 11216 of 216
Lettuce: Sow outdoorsApril 7June 11216 of 216
Lettuce: Sow for fallMay 30August 29198 of 216
Onion: Transplant or plant setsApril 7June 11216 of 216
Peas: Sow outdoorsApril 7June 11216 of 216
Peas: Sow for fallJune 3August 19209 of 216
Pepper: Transplant outdoorsMay 19July 9216 of 216
Potato: Plant seed potatoesApril 7June 25216 of 216
Pumpkin: Sow outdoorsMay 19July 9216 of 216
Radish: Sow outdoorsApril 7June 11216 of 216
Radish: Sow for fallJuly 9September 18216 of 216
Spinach: Transplant outdoorsApril 7June 11216 of 216
Spinach: Sow outdoorsApril 7June 11216 of 216
Spinach: Sow for fallJune 14September 1216 of 216
Summer squash: Transplant outdoorsMay 12July 2216 of 216
Summer squash: Sow outdoorsMay 5June 25216 of 216
Sweet corn: Sow outdoorsMay 5June 25216 of 216
Sweet potato: Plant slipsMay 12July 9216 of 216
Tomato: Transplant outdoorsMay 19July 9216 of 216
Turnip: Sow outdoorsApril 7June 11216 of 216
Turnip: Sow for fallJune 14August 29216 of 216
Watermelon: Transplant outdoorsMay 19July 9216 of 216
Watermelon: Sow outdoorsMay 19July 9216 of 216

Weather stations in Montana

Every station in Montana with NOAA frost-date normals, with its Typical 32°F frost dates and growing season. 29 of them have no 32°F frost dates.

Data sources

NOAA U.S. Climate Normals, frost dates, 1991–2020 normals, version 1.0.1
Files: us-climate-normals_1991-2020_v1.0.1_annualseasonal_multivariate_by-station_c20230404.tar.gz, inventory_30yr.txt from NOAA NCEI. Retrieved October 10, 2026.