Frost Dates and Growing Season by State

Key findings

• April 23Typical last spring frost at the median U.S. station
• October 20Typical first fall frost at the median station
• 179 daysMedian frost-free season
• 123 daysShortest state median: Montana
• 63 daysShortest season of any station: Moose 1 NNE, Wyoming
• 90Stations with fewer than 90 frost-free days in a typical year

The growing season, state by state

The frost-free season is the stretch between the last frost of spring and the first of fall, and it decides which crops a garden can finish. The shortest state medians are in the northern Rockies and Alaska: Montana (123 days), Alaska (124 days), Wyoming (125 days), Idaho (132 days). The longest are in the Deep South and California: Florida (334 days), California (281 days), Louisiana (268 days), Texas (247 days). In Hawaii, fewer than 3 stations see frost often enough for NOAA to date it, so no state median is shown.

A state median hides a lot. NOAA's network includes many mountain and valley stations, and within one state the season can differ by months: the shortest typical season anywhere is 63 days at Moose 1 NNE, Wyoming, followed by Moose, Wyoming (70 days) and Afton, Wyoming (71 days). At the other end, 92 stations, mostly in Florida and California, have no frost at all in a typical year, and another 119 see a frost in fewer than one year in ten, too rarely for NOAA to compute a date.

Latest spring frosts and earliest fall frosts

The latest typical last frosts are in June: Moose 1 NNE, Wyoming (June 24), Flagstaff 4 SW, Arizona (June 23), McCall, Idaho (June 22). The earliest typical first frosts arrive in August, in interior Alaska: Delta Junction 20 SE, Alaska (August 21), Gulkana AP, Alaska (August 21), Delta 5 NE, Alaska (August 22). Gardeners in those places plant cold-hardy, quick crops, start tender ones indoors and keep frost cloth handy all summer.

In the mildest states the median first "fall" frost can land in early January, after New Year; we count those dates as the end of the same season. Download the state table (CSV).

Twelve big cities

A city's own station can sit weeks away from its state median, in either direction. These are the same twelve stations our frost dates lookup shows as a reference.

How we worked it out

NOAA's U.S. Climate Normals for 1991 to 2020 include frost and freeze probabilities for every station with a long enough record. For each station, NOAA reports the date by which the last 32 °F night of spring has passed, and the date by which the first one of fall has arrived, at levels of risk from 10% to 90%. We use the 50% date as typical, the 10% date as a late last frost or an early first frost, and NOAA's own 50% frost-free season length. We downloaded NOAA's archive of station normals, extracted the frost columns without changing a value, and kept the extract with this site's code; a test compares it with NOAA's original file for one station, value for value. The methodology page has the details.

A state's figure is the median over its stations that have frost dates, so half the stations are earlier and half later. Stations are not spread evenly by population, so a state median describes the state's land, mountains included, more than where its people live. For your own garden, use the nearest station: our frost dates lookup finds it from a ZIP code, and the seed starting schedule counts back from it.

Use the data

Journalists, garden writers and Extension educators are welcome to use these figures and the map with credit to Frost and Seed and a link to this page. You can also put the station lookup on your own site with our free frost date widget. To check a number, contact us.