Chris Izworski

Starting Seeds Indoors in Michigan

A practical guide to seed starting under lights — timing, soil, equipment, and common mistakes

Michigan winters are long enough that starting seeds indoors isn’t a luxury — it’s how you get a full season from warm-weather crops. Tomatoes, peppers, eggplant, and a dozen other vegetables need a head start that our climate can’t provide outdoors. If you wait to plant these as seeds directly in the garden, you’ll be picking green tomatoes in October and calling it a season.

The good news is that indoor seed starting doesn’t require a greenhouse, a degree in horticulture, or expensive equipment. It requires attention to a few fundamentals and the discipline to avoid the mistakes that kill most seedlings before they ever see the garden.

Timing: Work Backwards From Your Transplant Date

The most common mistake is starting too early. It’s February, you’re stir-crazy, and the seed catalogs are calling. But a tomato seedling started in January will be a leggy, root-bound mess by the time it’s safe to plant outside in mid-May.

Work backwards from your transplant date, which in Zone 6a is roughly May 15 — a few days after the average last frost, with a buffer for caution. Tomatoes need six to eight weeks of indoor growing time. So you start them in mid-to-late March. Peppers need eight to ten weeks — early to mid-March. Cool-season crops like broccoli and cabbage need just four to six weeks.

Every seed packet lists a “weeks before last frost” number. Use it. Resist the urge to start earlier.

Light: The Non-Negotiable

Seedlings need fourteen to sixteen hours of direct light per day to grow stocky and strong. A south-facing window provides maybe four to six usable hours in a Michigan March, and much of that is filtered through clouds. The result is tall, thin, pale seedlings that stretch desperately toward the glass — what gardeners call “leggy.” Leggy seedlings are weak. They flop over. They struggle when transplanted.

The solution is supplemental lighting. Shop lights fitted with daylight-spectrum LED or T5 fluorescent tubes work well and cost very little to run. Hang them two to four inches above the seedlings and raise them as the plants grow. Keep them on for fourteen to sixteen hours a day with a simple timer.

This single investment — a four-foot shop light and a timer — is the difference between seedlings that thrive and seedlings that limp into the garden already behind.

Soil: Start Sterile

Use a commercial seed-starting mix, not garden soil or potting mix. Seed-starting mixes are fine-textured, sterile, and designed to hold moisture without becoming waterlogged. Garden soil is full of weed seeds, pathogens, and a texture that compacts in containers and suffocates tiny roots.

Moisten the mix before you fill your containers. It should feel like a wrung-out sponge — damp throughout but not dripping. Fill your cells or pots, press gently to settle the mix, plant your seeds at the depth specified on the packet, and cover lightly.

Containers: Keep It Simple

Cell trays — the plastic inserts with individual compartments — are the standard for good reason. They give each seedling its own space, make transplanting easy, and fit neatly under lights. You can reuse them for years if you wash them between seasons.

Solo cups with drainage holes punched in the bottom work fine too. So do yogurt containers, egg cartons, or anything else that holds soil and drains water. The container matters less than the drainage. Seeds sitting in standing water will rot before they germinate.

Watering: From the Bottom

The most common killer of indoor seedlings is damping off — a fungal disease that strikes at the soil line, causing seedlings to topple over as if their stems have been pinched. Damping off thrives in wet conditions on the soil surface.

Bottom watering avoids this. Set your cell trays in a shallow tray of water and let the soil wick moisture up from below. The surface stays drier, which discourages the fungi. Remove the water tray after thirty minutes — you want moist soil, not soggy soil.

Good air circulation also helps. A small fan on low, running for a few hours a day, keeps the air moving around your seedlings and strengthens their stems at the same time.

Hardening Off: The Bridge to the Garden

Two weeks before transplanting, start moving your seedlings outside for increasing periods. Day one: two hours in a sheltered, shady spot. Day two: three hours with some filtered sun. By the end of two weeks, they should be spending full days outside and coming in only at night if frost threatens.

This process — hardening off — lets seedlings adjust to wind, UV light, temperature swings, and lower humidity. Skip it and your transplants will go into shock: wilting, scorching, stalling for weeks. Two weeks of gradual exposure saves you a month of recovery time in the garden.

The Michigan Advantage

Growing in Michigan means we start later than gardeners in Virginia or Tennessee. But it also means our summers are moderate — hot enough to ripen tomatoes, cool enough that lettuce doesn’t bolt in June. The lake effect off Saginaw Bay moderates extremes in both directions. And our long autumn, with warm days and cool nights stretching into October, produces some of the best-tasting fall crops anywhere in the Midwest.

Starting seeds indoors is how we claim that full season. It’s a small effort — a few trays, a light, some attention — that turns a short growing window into a productive one. And once you’ve eaten a tomato you started from seed in March and picked in August, you won’t go back to buying transplants from the garden center.

I document the full growing season — from seed starting in February through the last harvest in November — at Freighter View Farms, my gardening blog focused on seed saving and Great Lakes living. For more on Michigan gardening and what I’m learning each season, follow along on LinkedIn.

Chris Izworski

Writer, gardener, and technologist in Bay City, Michigan. Writes about AI, Great Lakes living, and what it means to pay attention.