Illinois · zones 5b–6b
When to plant potatoes in Illinois.
Sow between Mar 13 to Apr 15 in a typical year, keyed to Illinois's median last frost around Apr 20. A second, fall sowing fits Jun 30 to Jul 13. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Potatoes dates for a typical Illinois season.
Direct sow
Mar 13 to Apr 15
Keyed to the ~Apr 20 last frost. Sow 4" deep, 12" apart.
Fall round
Jun 30 to Jul 13
Counted back from the ~Oct 18 first frost.
Harvest
~90 days later
~3 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.
In Illinois: watch for
The pests that find potatoes here.
A middle-length season, about 181 frost-free days, means potato overlaps colorado potato beetle for a stretch each summer. Check plants every week or two and treat early.
Striped beetles and orange grubs eating the leaves.
Organic fix: Handpick adults, crush the orange egg clusters, dust with diatomaceous earth.
Dark greasy blotches after cool, wet spells.
Organic fix: Pull infected plants fast, keep leaves dry, use neem as a preventive.
Common scab
Rough, corky patches on the skin, raised on some tubers and sunk into pits on others.
Organic fix: Keep the bed evenly moist through the weeks right after tubers set, rotate away from potatoes, and pick a scab-resistant variety next time.
Your season math: Illinois gives potatoes about 181 frost-free days, and it needs roughly 90 days to a first harvest. It's a one-planting crop, so time that single sowing well.
Planting potatoes in Illinois: questions
When should I plant potatoes in Illinois?+
In a typical Illinois year, sow potatoes between Mar 13 to Apr 15, keyed to the state's median last frost around Apr 20. There's also a fall window: Jun 30 to Jul 13. Your exact dates shift with your ZIP code and microclimate.
What USDA zone is Illinois?+
Illinois spans zones 5b–6b, mostly zone 6. But frost dates, not zones, set planting time. The free planner uses your ZIP code's actual frost dates.
How many potatoes plants do I need?+
Depends who you're feeding. The crop page has exact counts per household size, or the free planner does the math for your family in about 60 seconds.