Ontonagon, MI 49912 Frost Dates
Frost dates for Ontonagon, MI, ZIP 49912
Around 05/31 is the usual last spring frost, about 276 days away. The first fall frost typically arrives around 09/19, about 111 frost-free days later.
The USDA Plant Hardiness Zone Map puts Ontonagon 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 Ontonagon 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 Ontonagon's last frost
05/31 is the middle of 30 years of NOAA records, not a promise. Plant by 05/16 and you're betting against frost in roughly 9 years out of 10. 06/13 is the safer bet, historically only a 1-in-10 chance of frost that late.
How Ontonagon compares
At roughly 111 frost-free days, Ontonagon places 39,469 of 40,283 ZIP codes in this dataset. Within MI, it ranks 1,127 of 1,153.
Learn more
the frost range explains how to read the range around Ontonagon's dates instead of trusting one, and local microclimates explains what one yard in Ontonagon can differ from the 49912 normal.