Grass Lake, MI 49240 Frost Dates
49240, near Grass Lake, MI: the frost window
Typically, the last spring freeze lands around 04/30, roughly 245 days out. Fall's first freeze usually shows up around 10/12, roughly 163 days after the last spring frost.
Zone 6a (-10 to -5°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 Grass Lake, not a forecast for this year.
Stretching the season past the first frost
Grass Lake's growing season runs out in roughly 6 weeks — a cold frame or greenhouse kit is the usual way to keep cool-weather crops going past the first frost.
How much risk comes with planting early here
04/30 is the middle of 30 years of NOAA records, not a promise. Getting tender plants in by 04/18 carries real risk, frost has hit that late in about 9 of 10 years here. Wait until 05/17 and only about 1 year in 10 sees frost after that.
Grass Lake against the rest of the dataset
At roughly 163 frost-free days, Grass Lake places 31,453 of 40,283 ZIP codes in this dataset. Within MI, it ranks 519 of 1,153.
Learn more
Two guides worth reading on 49240: zone vs. frost date, on why Zone 6a and Grass Lake's frost date answer different questions, and the frost range, on how to read the range around Grass Lake's dates instead of trusting one.