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Frost Dates and Planting Windows in Colorado

The 32°F frost dates at the 210 weather stations in Colorado 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 Colorado

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 April 20 to June 28 across the state, and the first frost from August 28 to October 19.

32°F frost dates: earliest and latest among 210 stations, by risk level
Risk levelEarliest last frostLatest last frostEarliest first frostLatest first frost
Conservative (10%)April 28GRAND JUNCTION WFO, CO USJuly 9VAIL, CO USAugust 17BOULDER 14 W, CO USOctober 12PALISADE, CO US
Typical (30%)April 20GRAND JUNCTION WFO, CO USJune 28VAIL, CO USAugust 28BOULDER 14 W, CO USOctober 19PALISADE, CO US
Aggressive (50%)April 14GRAND JUNCTION WFO, CO USJune 213 stationsSeptember 2BOULDER 14 W, CO USOctober 26PALISADE, CO 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 210 stations
Risk levelShortestLongest
Conservative (90% chance of at least this long)51 daysBOULDER 14 W, CO US172 daysGRAND JUNCTION WFO, CO US
Typical (70% chance of at least this long)64 daysBOULDER 14 W, CO US183 daysGRAND JUNCTION WFO, CO US
Aggressive (50% chance of at least this long)71 daysBOULDER 14 W, CO US190 days2 stations
Number of stations by growing season length, Typical (70% chance of at least this long)
Growing seasonStations
60–79 days13
80–99 days19
100–119 days37
120–139 days48
140–159 days80
160–179 days11
180–199 days2

Planting windows across Colorado

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 4July 12210 of 210
Bean: Sow outdoorsApril 20June 28210 of 210
Beet: Sow outdoorsMarch 23June 28210 of 210
Beet: Sow for fallJune 15August 30191 of 210
Broccoli: Transplant outdoorsMarch 23June 14210 of 210
Broccoli: Transplant for fallJune 5August 30193 of 210
Brussels sprouts: Transplant outdoorsMarch 23June 14210 of 210
Brussels sprouts: Transplant for fallMay 22September 9172 of 210
Cabbage: Transplant outdoorsMarch 23June 14210 of 210
Cabbage: Transplant for fallMay 31August 30190 of 210
Cantaloupe: Transplant outdoorsMay 4July 12210 of 210
Cantaloupe: Sow outdoorsMay 4July 12210 of 210
Carrot: Sow outdoorsMarch 23June 28210 of 210
Carrot: Sow for fallJune 9August 20178 of 210
Cucumber: Transplant outdoorsApril 27July 5210 of 210
Cucumber: Sow outdoorsApril 20June 28210 of 210
Eggplant: Transplant outdoorsMay 4July 12210 of 210
Garlic: Plant for fallAugust 28November 2210 of 210
Lettuce: Transplant outdoorsMarch 23June 14210 of 210
Lettuce: Sow outdoorsMarch 23June 14210 of 210
Lettuce: Sow for fallJune 5September 9193 of 210
Onion: Transplant or plant setsMarch 23June 14210 of 210
Peas: Sow outdoorsMarch 23June 14210 of 210
Peas: Sow for fallJune 8August 30203 of 210
Pepper: Transplant outdoorsMay 4July 12210 of 210
Potato: Plant seed potatoesMarch 23June 28210 of 210
Pumpkin: Sow outdoorsMay 4July 12210 of 210
Radish: Sow outdoorsMarch 23June 14210 of 210
Radish: Sow for fallJuly 10September 29210 of 210
Spinach: Transplant outdoorsMarch 23June 14210 of 210
Spinach: Sow outdoorsMarch 23June 14210 of 210
Spinach: Sow for fallJune 15September 12210 of 210
Summer squash: Transplant outdoorsApril 27July 5210 of 210
Summer squash: Sow outdoorsApril 20June 28210 of 210
Sweet corn: Sow outdoorsApril 20June 28210 of 210
Sweet potato: Plant slipsApril 27July 12210 of 210
Tomato: Transplant outdoorsMay 4July 12210 of 210
Turnip: Sow outdoorsMarch 23June 14210 of 210
Turnip: Sow for fallJune 15September 9210 of 210
Watermelon: Transplant outdoorsMay 4July 12210 of 210
Watermelon: Sow outdoorsMay 4July 12210 of 210

Weather stations in Colorado

Every station in Colorado with NOAA frost-date normals, with its Typical 32°F frost dates and growing season. 24 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.