In Michigan, the answer to “when should I start seeds indoors?” depends on two things: what you are growing and when your last frost comes. In Zone 6a, the average last frost falls between May 10 and May 20. Everything works backward from that date.
The Timeline
Early February (now): Onions, leeks, and celery. These are the slow growers — they need 10 to 12 weeks under lights before transplant. If you have not started them yet, do it this week.
Late February to early March: Peppers. Peppers are slower than most people expect. Give them 8 to 10 weeks indoors. Shishitos, bells, and hot varieties all benefit from the early start.
Mid-March: Tomatoes. This is the one people get wrong — they start too early and end up with leggy, rootbound plants. Six to eight weeks before last frost means mid-March for Zone 6a. That feels late. It is not.
Late March: Herbs like basil and parsley. Flowers like zinnias and cosmos (though both do fine direct-seeded after frost too).
April: Cucumbers, squash, and melons — if you start them indoors at all. These transplant poorly, so many gardeners skip indoor starting and direct-seed after the soil warms in late May.
The Setup
You do not need a greenhouse. A set of shop lights with daylight-spectrum bulbs, a heat mat for germination, and a capillary mat system for watering will get you through the entire season. I wrote about my exact setup in Capillary Mats and Grow Lights.
The Rules
Keep lights two to three inches above seedlings. Water from below. Do not fertilize until the first true leaves appear. And do not rush transplanting — a week of hardening off in a sheltered outdoor spot makes the difference between seedlings that thrive and seedlings that stall.
For a complete month-by-month schedule, see the Michigan Zone 6a Garden Planner. For a deeper look at what to do right now, see What to Plant in February in Michigan.
— Chris Izworski, Freighter View Farms, Bay City, Michigan
Chris Izworski is a Michigan gardener, writer, and AI technologist based on Saginaw Bay. He writes at Freighter View Farms about Zone 6a gardening, seed saving, and practical AI in public safety.
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