Ismay, MT 59336 Frost Dates
Frost dates for Ismay, MT, ZIP 59336
Around 05/22 is the usual last spring frost, about 267 days away. The first fall frost typically arrives around 09/15, about 117 frost-free days later.
The USDA Plant Hardiness Zone Map puts Ismay in Zone 4a (-30 to -25°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 4a around Ismay 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.
How much risk comes with planting early here
05/22 is the middle of 30 years of NOAA records, not a promise. Plant by 05/09 and you're betting against frost in roughly 9 years out of 10. 06/07 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Ismay compares
Ismay's growing season runs about 117 days, ranking 39,269 of 40,283 US ZIP codes measured here, longest to shortest. Within MT, it ranks 237 of 392.
Learn more
local microclimates explains what one yard in Ismay can differ from the 59336 normal, and zone vs. frost date explains why Zone 4a and Ismay's frost date answer different questions.