Illinois · zones 5b–6b
When to plant tomatoes in Illinois.
Sow or transplant between Apr 27 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
Tomatoes dates for a typical Illinois season.
1 · Start indoors
Mar 16 to May 16
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Apr 27 to Jun 27
Keyed to the ~Apr 20 last frost. Sow 0.25" deep, 24" apart.
Harvest
~73 days later
~12 lb per plant over ~8 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 tomatoes here.
A middle-length season, about 181 frost-free days, means tomato, slicing overlaps tomato hornworm for a stretch each summer. Check plants every week or two and treat early.
Big green caterpillars strip leaves and leave black droppings.
Organic fix: Handpick at dusk; spray Bt on the young ones.
Clusters on new growth, sticky leaves, curling tips.
Organic fix: Blast with water, then insecticidal soap or neem.
Dark spots with concentric rings, starting on the lowest, oldest leaves.
Organic fix: Remove affected leaves, mulch to stop soil splash, space for airflow.
Greasy, water-soaked blotches in cool, wet spells. No rings, and not bottom-up.
Organic fix: Pull infected plants fast, keep leaves dry, use neem as a preventive.
Septoria leaf spot
Many small tan spots with dark brown edges, low leaves first, no rings inside.
Organic fix: Strip the lowest leaves, mulch against soil splash, stake for airflow.
Your season math: Illinois gives tomatoes about 181 frost-free days, and it needs roughly 73 days to a first harvest. It's a one-planting crop, so time that single sowing well.
Planting tomatoes in Illinois: questions
When should I plant tomatoes in Illinois?+
In a typical Illinois year, sow tomatoes or set out transplants between Apr 27 to Jun 27, keyed to the state's median last frost around Apr 20. Your exact dates shift with your ZIP code and microclimate.
When do I start tomatoes seeds indoors in Illinois?+
Start seeds inside about 6 weeks before set-out: roughly Mar 16 to May 16 for a typical Illinois season.
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 tomatoes 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.