Illinois · zones 5b–6b
When to plant sweet potatoes in Illinois.
Sow or transplant between May 27 to Jul 11 in a typical year, keyed to Illinois's median last frost around Apr 20. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Sweet Potatoes dates for a typical Illinois season.
1 · Start indoors
Apr 15 to May 30
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
May 27 to Jul 11
Keyed to the ~Apr 20 last frost. Sow 3" deep, 14" apart.
Harvest
~110 days later
~2.5 lb per plant over ~1 weeks.
Illinois spans more than one climate: Zone 6 is the most common zone, but the state runs 5b to 6b. That's why the planner works from your ZIP code's frost dates, not your zone — mountain and coastal gardens in the same state can be three weeks apart.