Why Seed Starting Matters in Michigan
Michigan's short growing season — as few as 100 days in zone 4a — means starting key crops indoors is not optional. It's the difference between a full harvest and a disappointing one. Starting your own seeds also saves $200–$400 a season versus buying transplants.
When to Start Seeds by Michigan Zone
Your last frost date drives everything. Use the table below to find your zone's start window.
| Crop | Zone 4a–5a (U.P.) | Zone 5b (N. LP) | Zone 6a (Grand Rapids/Lansing) | Zone 6b (Detroit) |
|---|---|---|---|---|
| Tomatoes | March 15 – Apr 1 | Mar 20 – Apr 5 | Apr 1–15 | Apr 5–15 |
| Peppers | Mar 1–15 | Mar 5–20 | Mar 15 – Apr 1 | Mar 20 – Apr 1 |
| Eggplant | Mar 1–15 | Mar 5–20 | Mar 15 – Apr 1 | Mar 20 – Apr 1 |
| Brassicas (broccoli, cabbage) | Mar 1–15 | Mar 5–20 | Mar 10–25 | Mar 15–25 |
| Cucumbers / Squash | May 1–10 | Apr 25 – May 5 | Apr 20 – May 1 | Apr 15–25 |
| Basil | Apr 15–25 | Apr 10–20 | Apr 1–15 | Apr 1–10 |
| Lettuce | Feb 15 – Mar 1 | Feb 20 – Mar 5 | Mar 1–15 | Mar 1–10 |
What You Actually Need
The Step Most Beginners Skip
Hardening off — gradually exposing indoor seedlings to outdoor conditions — is critical in Michigan where late-season cold snaps are common even into May.
- Day 1–2: Shaded outdoor time, 1–2 hours
Start on a calm, mild day (55°F+). Place seedlings in bright shade — not direct sun. Bring them back in before evening.
- Day 3–4: Dappled sun, 2–3 hours
Increase exposure gradually. Watch for wilting — a sign of sun or wind stress. Water before if soil feels dry.
- Day 5–7: Direct sun, morning only
Introduce direct morning sun. Avoid harsh afternoon sun during this phase — it can scorch leaves.
- Day 8–10: Full day outdoors
Leave plants out all day. Check overnight lows — if frost threatens, bring them back in. Never leave tender transplants out if temps drop below 45°F.
- Day 10–14: Overnight outdoors (weather permitting)
Once nights are consistently above 50°F and plants have been through a few full outdoor days, they're ready to plant.