When to plant sweet corn in USDA Zone 4a

Plan your sweet corn 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.

Fargo ND, northern MN, northern WI, northern ME. Average last spring frost May 22, first fall frost September 15 — a 116-day frost-free season.

Zone fit: good
Sweet corn 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

Direct-seed outdoors
May 22 – June 12
Expected first harvest
August 12 – September 9
Fall planting window
June 16 – July 7
Fall harvest window
September 6 – October 4

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
12″
Row spacing
30″
Seed depth
1.5″
Soil temperature
65–85°F
Frost tolerance
tender
Days to harvest
75 days

Grower notes for Zone 4a

Plant in blocks of 4+ rows for wind pollination. Isolate super-sweet varieties from standard varieties by 250 ft or 14 days.

Plant near: beans, squash, cucumbers

Keep away from: tomatoes

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.