When to plant sweet corn in Illinois
Illinois’s average last spring frost is April 20, and the first fall frost typically arrives around October 14 — about 177 frost-free days (USDA zones 5a, 5b, 6a, 6b, 7a). Sweet Corn needs 60–100 days to mature, which fits comfortably within Illinois's growing season.
When to plant sweet corn in Illinois: the short answer
For a spring planting, sow Apr 22 – May 11. Wait until the soil is at least 55°F and frost is over.
Succession sow again in Illinois: May 11 · May 25 · Jun 8 · Jun 22 · Jul 6 · Jul 20
Windows are ~1–2 week bands around each date. Frost dates are a statewide average from NOAA/NCEI normals; your town may differ by two weeks or more. Calendar year 2026.
How to grow sweet corn in Illinois, step by step
- Prepare the bed. It needs at least six to eight hours of direct sun a day and loose soil at least 24 inches deep, with a pH between 5.8 and 7.0. Dig in compost before planting.
- Sow outdoors (Apr 22 – May 11). Space plants about 10 inches apart in rows 30 inches apart, sowing seed 1.5 inches deep. It is killed by frost, so nothing goes outside until the danger has passed.
- Water and feed. It needs plenty of water; keep the soil evenly moist and never let it dry out.
- Watch for pests and problems. Pests: corn earworm, European corn borer, corn rootworm, raccoons. Diseases and disorders: common smut, common rust, Stewart's wilt.
- Harvest (from about Jun 26 – Aug 5). Sweet Corn takes 60-100 days to reach harvest. Plant in a block of at least 4 short rows, not one long row, or the ears fill unevenly. Keep sugar-enhanced and supersweet types isolated from field corn. Succeed by sowing every 2 weeks or planting early/mid/late varieties together.
Figures come from our crop data; dates use Illinois’s average frost dates. More in the full sweet corn growing guide.
Sweet Corn planting dates by USDA zone in Illinois
Illinois spans USDA zones 5a, 5b, 6a, 6b, 7a. Colder zones, usually higher or further inland, have a later last spring frost and an earlier first fall frost than the state average, so the sweet corn dates shift with them.
When to plant sweet corn in nearby states
Questions gardeners in Illinois ask
When is the best time to plant sweet corn in Illinois?
Sow sweet corn in Illinois between April 22 and May 11. That timing is set by Illinois's average last spring frost of April 20.
What is the latest I can plant sweet corn in Illinois?
About August 15. Sweet corn needs at least 60 days to mature, and frost around October 14 ends the season, so later plantings risk being cut short.
When will sweet corn planted in Illinois be ready to harvest?
Planted on time, sweet corn is usually ready from about June 26 to August 5, 60-100 days after sowing.
When is the last frost in Illinois?
On average around April 20, with the first fall frost around October 14 - about 177 frost-free days. Your town may differ by two weeks or more.