Harlowton, MT 59036 Frost Dates
Frost dates for Harlowton, MT, ZIP 59036
Around 05/23 is the usual last spring frost, about 268 days away. The first fall frost typically arrives around 09/16, about 113 frost-free days later.
The USDA Plant Hardiness Zone Map puts Harlowton in Zone 4b (-25 to -20°F average annual minimum); frost dates are NOAA's 1991-2020 station normal, not this year's forecast.
What to do before the first frost
Zone 4b around Harlowton has about 3 weeks left before the first fall frost — that's the usual window to get a cold frame up if you want to keep harvesting past it.
The actual range around Harlowton's last frost
05/23 is the middle of 30 years of NOAA records, not a promise. Plant by 05/12 and you're betting against frost in roughly 9 years out of 10. 06/06 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Harlowton compares
At roughly 113 frost-free days, Harlowton places 39,400 of 40,283 ZIP codes in this dataset. Within MT, it ranks 259 of 392.
Learn more
local microclimates explains what one yard in Harlowton can differ from the 59036 normal, and zone vs. frost date explains why Zone 4b and Harlowton's frost date answer different questions.