Mahnomen, MN 56557 Frost Dates
Frost dates for Mahnomen, MN, ZIP 56557
Around 05/07 is the usual last spring frost, about 252 days away. The first fall frost typically arrives around 09/28, about 143 frost-free days later.
The USDA Plant Hardiness Zone Map puts Mahnomen 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 Mahnomen has about 4 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 05/07 isn't a guarantee
05/07 is the middle of 30 years of NOAA records, not a promise. Plant by 04/27 and you're betting against frost in roughly 9 years out of 10. 05/24 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Mahnomen compares
At roughly 143 frost-free days, Mahnomen places 36,559 of 40,283 ZIP codes in this dataset. Within MN, it ranks 678 of 943.
Learn more
the frost range explains how to read the range around Mahnomen's dates instead of trusting one, and local microclimates explains what one yard in Mahnomen can differ from the 56557 normal.