Michigan Frost Dates by City

Frost dates vary significantly across Michigan due to the moderating effect of the Great Lakes, elevation changes, and urban heat islands. The data below is based on NOAA 30-year climate normals (1991–2020) for a 32°F threshold.

The most important variable for gardeners near the Great Lakes is the lake effect thermal buffer. Lakeshore locations in western Michigan — Muskegon, Holland, Benton Harbor — consistently run 2 to 3 weeks longer in growing season than inland locations at the same latitude. The same pattern holds along Lake Huron's shoreline near Bay City and Saginaw Bay, though less dramatically. Bay City's average last frost date of May 6 is later than you might expect for a lakeshore location because Saginaw Bay is shallower and warms faster than Lake Michigan — the buffering effect is real but smaller than on the western shore.

These dates are 30-year averages and represent the date by which there is a 50% probability of frost. For a more conservative planting date — meaning a 90% chance that frost is done — add 1 to 2 weeks to the last spring frost date shown. The Zone 6a planting calendar uses these frost windows to build crop-specific transplant timing for the Bay City region. For broader context on Zone 6a Michigan growing conditions, see the Michigan gardening overview.

Lower Peninsula, Last Spring / First Fall Frost

Upper Peninsula