Michigan Frost Dates

Every station in the Michigan State Climatologist's frost probability table, searchable and sorted your way, with typical fall dates and season lengths. Maintained by Chris Izworski in Bay City.

Ask when Michigan's last frost is and you will get a shrug or a wrong answer, because the honest answer is a table, not a date. The state's frost map runs from Detroit's city core, where the median last freeze lands April 24, to the high interior around Vanderbilt, where it lands June 20, a spread of eight weeks inside one state. Below is the complete table: for each of 78 stations, the earliest last frost on record, the 75, 50, and 25 percent probability dates, and the latest freeze ever recorded there. The bolded median is the planning date; everything else tells you how much the place likes to surprise you.

Last spring frost probabilities, all 78 stations

Reading it: at Bay City the median is May 2, meaning half of springs still frost after that date. The cautious 25 percent date is May 9. The latest freeze on record is May 26, which is why the old timers wait for Memorial Day. Source: Michigan State Climatologist Office, published by MSU Extension.

Typical first fall frost

Fall works differently. The spring table above is the State Climatologist's probability math; comparable official fall probabilities are not published in one table, so the dates below are typical medians drawn from the 1991 to 2020 NOAA climate normals, good to about a week either way. Two patterns dominate. The big lakes hold summer's heat, so the Lake Michigan shore, Saginaw Bay, and the Superior shoreline stay frost free one to three weeks longer than ground a few miles inland. And cold air drains into the sandy interior highlands, which is why Gaylord can freeze in the first days of September while Detroit grows tomatoes to Halloween.

Growing season length, median to median

Subtract the median last spring frost from the typical first fall frost and you get the honest length of the frost free season. The table sorts longest to shortest, and the spread says everything about gardening in this state: a Detroit gardener gets more than twice the frost free days of a Vanderbilt gardener, 130 miles apart.

Cold pockets: why the map ignores latitude

The strangest rows in the spring table are not in the Upper Peninsula. Marquette's median is May 13; Vanderbilt, 200 miles south of it, is June 20. Grayling, Fife Lake, Atlanta, and Houghton Lake all run two to four weeks colder than their latitude suggests. The reason is landform: the northern Lower Peninsula's high sandy outwash plains sit above the lake influence, radiate heat on clear nights, and collect the cold air that drains off the surrounding hills. If you garden in that country, the local wisdom that frost can come any month of the year is not folklore, it is the station record. Grayling's latest spring freeze on record is July 21.

Lakeshore grace

The mirror image is the shoreline. Grand Haven, Holland, Muskegon, and South Haven pick up spring frost protection from a cold Lake Michigan that suppresses early warmth, then repay it in fall when the warm lake holds frost off well into October, which is exactly why the fruit belt is where it is. Saginaw Bay does the same smaller favor for Bay City: the shoreline gardens run a week or more past the ground five miles inland. If you can see big water from your garden, trust the later fall dates; if you are in a low spot behind the first ridge, do not.

About hardiness zones

Frost dates and hardiness zones answer different questions. Zones describe average winter minimums and tell you which perennials survive; the 2023 USDA update shifted much of lower Michigan about half a zone warmer, putting the Bay City area on the 6a to 6b line. None of that moves a frost date. For deciding when to sow and transplant, use the tables on this page, or better, the planting calendar, which turns any station above into a full schedule for 47 crops.

When frost is forecast anyway

A frost date is a probability; a frost forecast is a Tuesday. When one is coming, the cheap defenses work: water the beds in the afternoon because damp soil holds and releases more heat overnight, cover tender crops before sunset with row cover, sheets, or overturned buckets so the ground's warmth is trapped rather than the plant alone, and pull the covers after sunrise. A degree or two of protection is usually the whole game, and most frost nights in the shoulder seasons are one bad hour just before dawn.

Common questions

What is the last frost date for Detroit?

The city station's median is April 24, with April 30 as the cautious date and May 12 the latest on record. The metro airport runs about a week colder: May 3 median.

What is the last frost date for Grand Rapids?

May 2 median, May 10 cautious, May 27 latest recorded.

What is the last frost date for Traverse City?

May 23 median, June 1 cautious, and the record is July 6, a reminder that the bay moderates the town while the inland hills do their own thing.

When is it safe to plant tomatoes?

One to three weeks after your station's median, once nights hold above 50. The calendar computes it per station.