When to plant sweet potatoes in USDA Zone 3b

Plan your sweet potatoes 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.

Grand Forks & Minot ND, northern MN border counties. Average last spring frost May 25, first fall frost September 10 — a 108-day frost-free season.

Zone fit: challenging
Sweet potatoes needs a long season and this zone averages just 108 frost-free days. Start early, use black plastic, and plan for row cover on shoulder-season frosts.

Key dates

Start seeds indoors
April 6 – April 20
Transplant outdoors
June 8 – June 29
Expected first harvest
September 23 – October 21

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
42″
Seed depth
4″
Soil temperature
75–90°F
Frost tolerance
tender
Days to harvest
100 days

Grower notes for Zone 3b

Set slips on 6–8 inch hills for better tuber shape. Cure at 85°F and 85% humidity for 7–10 days after harvest.

Plant near: beans, peas

Keep away from: squash

Other root crops for Zone 3b

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.