Reference Data
Zone 6a Michigan Planting Calendar
Zone 6a covers most of Michigan's lower peninsula, with average minimum winter temperatures between -10°F and -5°F. The Great Lakes moderate temperatures along the shoreline, creating microclimates that can extend the growing season by 1–2 weeks.
Frost Dates
May 10Average Last Spring Frost
Oct 5Average First Fall Frost
148 daysAverage Growing Season
Zone 6aUSDA Hardiness Zone
Vegetable Planting Schedule
| Crop | Start Indoors | Transplant Outside | Direct Sow | Notes |
|---|
| Tomatoes | Mar 15 – Apr 1 | May 20 – Jun 1 | — | After last frost, soil 60°F+ |
| Peppers | Mar 1 – Mar 15 | May 25 – Jun 5 | — | Needs warm soil, slow to establish |
| Eggplant | Mar 1 – Mar 15 | May 25 – Jun 5 | — | Warm season, frost sensitive |
| Cucumbers | Apr 20 – May 1 | May 25 – Jun 1 | May 25 – Jun 1 | Direct sow preferred |
| Squash (summer) | Apr 20 – May 1 | May 25 – Jun 1 | May 25 – Jun 1 | Direct sow preferred |
| Squash (winter) | — | — | May 20 – Jun 1 | Needs 90–110 days to maturity |
| Beans (bush) | — | — | May 15 – Jun 15 | Sow every 2 weeks for succession |
| Beans (pole) | — | — | May 20 – Jun 1 | Need trellis, longer season |
| Peas | — | — | Apr 1 – Apr 20 | Cool season, plant as soon as soil workable |
| Lettuce | Mar 15 – Apr 1 | Apr 20 – May 10 | Apr 15 – May 1 | Bolt-resistant varieties for summer |
| Spinach | — | — | Apr 1 – Apr 20 | Cool season, spring and fall |
| Kale | Mar 15 – Apr 1 | Apr 20 – May 10 | Apr 15 – May 10 | Tolerates light frost |
| Broccoli | Mar 1 – Mar 15 | Apr 20 – May 5 | — | Spring and fall crops possible |
| Cabbage | Mar 1 – Mar 15 | Apr 20 – May 5 | — | Hardy, tolerates frost |
| Carrots | — | — | Apr 15 – May 10 | Loose, deep soil; succession sow |
| Beets | — | — | Apr 15 – May 15 | Greens and roots both edible |
| Onions | Feb 15 – Mar 1 | Apr 15 – May 1 | Apr 15 – May 1 | Long season, start early indoors |
| Garlic | — | — | Oct 1 – Oct 20 | Fall planted, harvested July |
| Potatoes | — | — | Apr 20 – May 10 | Plant seed potatoes 2–4 weeks before last frost |
| Sweet corn | — | — | May 15 – Jun 1 | Soil must be 60°F+ |
| Sunflowers | — | — | May 10 – Jun 1 | Direct sow after last frost |
| Melons | Apr 20 – May 1 | May 25 – Jun 5 | — | Short-season varieties recommended for Zone 6a |
Herb Planting Schedule
| Herb | Start Indoors | Transplant / Direct Sow | Notes |
|---|
| Basil | Apr 1 – Apr 20 | May 25 – Jun 5 | Very frost sensitive |
| Parsley | Feb 15 – Mar 1 | Apr 20 – May 10 | Slow germinator, biennial |
| Dill | — | Apr 20 – May 10 | Direct sow, does not transplant well |
| Cilantro | — | Apr 15 – May 1 | Bolts in heat; succession sow |
| Chives | Feb 15 – Mar 1 | Apr 20 – May 5 | Perennial in Zone 6a |
| Thyme | Feb 15 – Mar 1 | Apr 20 – May 10 | Perennial, woody herb |
| Sage | Feb 15 – Mar 1 | Apr 20 – May 10 | Perennial in Zone 6a |
| Rosemary | Feb 1 – Feb 15 | May 10 – May 25 | Borderline hardy in 6a; mulch well |
Flower Planting Schedule
| Flower | Start Indoors | Direct Sow / Transplant | Notes |
|---|
| Zinnia | Apr 15 – May 1 | May 20 – Jun 1 | Direct sow preferred after frost |
| Marigold | Mar 15 – Apr 1 | May 10 – May 25 | Pest deterrent, prolific bloomer |
| Calendula | Mar 1 – Mar 15 | Apr 20 – May 10 | Cool season, edible petals |
| Cosmos | — | May 10 – May 25 | Direct sow after frost |
| Larkspur | — | Sep 15 – Oct 1 or Apr 1 – Apr 15 | Fall or very early spring sow |
| Nasturtium | — | May 10 – May 25 | Direct sow, edible flowers and leaves |
| Sunflower | — | May 10 – Jun 1 | Direct sow after frost |
Dates are based on a May 10 average last frost for Bay City / Saginaw Bay area, Zone 6a. Adjust ±1 week based on your specific location and elevation. Lakeshore locations may have later spring frosts and earlier fall frosts due to lake effect.
Sources: USDA Plant Hardiness Zone Map; Michigan State University Extension; National Weather Service Detroit/Pontiac frost date records; Freighter View Farms field observations, Bay City MI.
Data compiled and maintained by
Chris Izworski — writer, technologist, and gardener based in Bay City, Michigan.