Michigan Zone 6a Planting Calendar by City

Pick your nearest Michigan city and this calendar computes indoor seed-starting, transplant, direct-sow, and fall-sow dates for 47 crops from local frost probabilities. Zone 6a gardeners around Bay City start from a median May 2 last spring frost, while colder Michigan locations run weeks later, so every crop recalculates instead of relying on one statewide date.

Interactive dates for 47 vegetables, herbs, and flowers, computed from Michigan State Climatologist frost probabilities for 78 stations. Built by Chris Izworski in Zone 6a, Bay City, and tuned for every corner of the state.

Vegetables

Herbs

Flowers

How these dates are computed

Every window on this page is an offset from your station's last spring frost, or from the typical first fall frost for the fall sowings. The spring anchors come from the Michigan State Climatologist Office's probability table, published through MSU Extension, which gives the chance of 32 degrees or colder occurring on or after a given date for 78 Michigan stations. The offsets are standard horticultural timing: tomatoes start indoors six to eight weeks before the last frost and go out a week or two after it, peas go in the ground four to six weeks before it, and so on, the same arithmetic gardeners have always done on the back of a seed packet, done here for every crop and every station at once.

What the calendar cannot tell you

Soil temperature outranks any calendar. A Bay City May can hand you 60 degree soil on the 10th one year and cold mud on the 25th the next, and warm season seed sown into cold mud rots rather than waits. A ten dollar soil thermometer settles the argument: 40s are for peas and spinach, 50s bring in the brassicas and roots, 60 opens the door for beans, corn, and tomatoes, and the cucurbits and melons want 65 to 70. When the calendar says go and the thermometer says wait, the thermometer is right.

Cold air drains downhill and pools, which is why the frost map of Michigan is really a map of landforms. Gardens on the Lake Michigan shore and around Saginaw Bay run later into fall than gardens ten miles inland; the high sandy interior around Grayling, Gaylord, and Vanderbilt can frost any month of the year. If your garden sits in a hollow, plan a week later in spring and a week earlier in fall than your station says. If it sits on a slope above open water, you are playing with house money.

One more mapping note: the 2023 USDA hardiness zone update shifted much of lower Michigan about half a zone warmer on paper, and the Bay City area now sits on the 6a to 6b line. Hardiness zones describe winter lows for perennials; they say nothing about frost dates, which is why this calendar runs on frost probabilities instead.

Common questions

When do I plant tomatoes in Michigan?

Start seed indoors six to eight weeks before your median last frost and transplant one to three weeks after it, once nights hold above 50 and the soil reads 60. In Bay City that means starting around mid March and planting out in mid to late May; in Detroit, two weeks earlier on both ends; in the northern interior, June planting is normal and nothing is wrong with your spring.

What can I plant before the last frost?

Plenty. Peas, spinach, radishes, lettuce, beets, carrots, onions, potatoes, sweet peas, and the brassica transplants all tolerate frost and prefer cool soil. Half the garden can be growing a month before the tomatoes are safe.

Is there time for a fall garden in Michigan?

Yes, and it is the most overlooked planting of the year. Count back from your first fall frost: kale, carrots, and beets sown in July, lettuce and spinach into August, radishes into September in the southern half of the state. The fall column above does that counting for your station.

When do I plant garlic?

In fall, after the first light frost and before the ground freezes: October for most of the Lower Peninsula, late September up north. It roots through winter and hands you bulbs the following July.