Chester, MT 59531 Frost Dates
Frost dates for Chester, MT, ZIP 59531
Around 05/21 is the usual last spring frost, about 266 days away. The first fall frost typically arrives around 09/19, about 119 frost-free days later.
The USDA Plant Hardiness Zone Map puts Chester 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 Chester 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
05/21 is the middle of 30 years of NOAA records, not a promise. Plant by 05/08 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 Chester compares
Chester's growing season runs about 119 days, ranking 39,155 of 40,283 US ZIP codes measured here, longest to shortest. Within MT, it ranks 222 of 392.
Learn more
local microclimates explains what one yard in Chester can differ from the 59531 normal, and zone vs. frost date explains why Zone 4a and Chester's frost date answer different questions.