Ontonagon, MI 49960 Frost Dates
49960, near Ontonagon, MI: the frost window
Around 05/27 is the usual last spring frost, about 272 days away. Fall's first freeze usually shows up around 10/01, roughly 127 days after the last spring frost.
Zone 4b (-25 to -20°F average annual minimum) comes from the USDA Plant Hardiness Zone Map; the frost dates above are the 1991-2020 normal at the nearest reporting NOAA station for Ontonagon, not a forecast for this year.
Stretching the season past the first frost
Ontonagon's growing season runs out in roughly 5 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
Why 05/27 isn't a guarantee
05/27 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 05/07 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 06/13 and only about 1 year in 10 sees frost after that.
Ontonagon against the rest of the dataset
Ontonagon's growing season runs about 127 days, ranking 38,640 of 40,283 US ZIP codes measured here, longest to shortest. Within MI, it ranks 1,062 of 1,153.
Learn more
Two guides worth reading on 49960: the frost range, on how to read the range around Ontonagon's dates instead of trusting one, and local microclimates, on what one yard in Ontonagon can differ from the 49960 normal.