Malta, MT 59538 Frost Dates
Frost dates for Malta, MT, ZIP 59538
Around 05/10 is the usual last spring frost, about 255 days away. The first fall frost typically arrives around 09/29, about 139 frost-free days later.
Malta sits in USDA Zone 4a (-30 to -25°F average annual minimum). The dates above are NOAA's 1991-2020 normal at the nearest reporting station, a 30-year average, not a forecast.
What to do before the first frost
Zone 4a around Malta has about 5 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.
Why 05/10 isn't a guarantee
05/10 is the middle of 30 years of NOAA records, not a promise. Plant by 04/29 and you're betting against frost in roughly 9 years out of 10. 05/22 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Malta compares
At roughly 139 frost-free days, Malta places 37,236 of 40,283 ZIP codes in this dataset. Within MT, it ranks 69 of 392.
Learn more
local microclimates explains what one yard in Malta can differ from the 59538 normal, and zone vs. frost date explains why Zone 4a and Malta's frost date answer different questions.