Illinois · zones 5b–6b
When to plant watermelon in Illinois.
Sow between May 11 to Jun 27 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
Watermelon dates for a typical Illinois season.
Direct sow
May 11 to Jun 27
Keyed to the ~Apr 20 last frost. Sow 1" deep, 36" apart.
Harvest
~85 days later
~20 lb per plant over ~3 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.