When to plant tomatoes in USDA Zone 4b

Plan your tomatoes planting around local frost risk and soil temperature, then work backward from the harvest week your buyers need. The calendar below is a starting point, not a field-level weather forecast.

Minneapolis, Duluth, central WI, northern VT/NH. Average last spring frost May 15, first fall frost September 22 — a 130-day frost-free season.

Zone fit: good
Tomatoes is frost-tender, so timing the outdoor transplant to the last frost matters more here than in warmer zones. Row cover buys 2 weeks of head start.

Key dates

Start seeds indoors
March 27 – April 10
Transplant outdoors
May 22 – June 12
Expected first harvest
August 12 – September 9
Fall planting window
June 9 – June 30
Fall harvest window
August 30 – September 27

Windows are calculated from your zone's average frost dates. Adjust ±1 week for microclimates, elevation, and your own frost records.

Spacing and soil

Plant spacing
24″
Row spacing
48″
Seed depth
0.25″
Soil temperature
70–85°F
Frost tolerance
tender
Days to harvest
75 days

Grower notes for Zone 4b

Set transplants deep — bury two-thirds of the stem to encourage adventitious roots. Stake or cage before fruit set.

Plant near: basil, carrots, onions

Keep away from: brassicas, corn, fennel

Other nightshades for Zone 4b

Same crop, other zones

Track your own plantings

BAU Farm Intelligence turns these windows into per-field tasks — indoor seed-start reminders, transplant dates, harvest projections — using your farm's actual frost history.