When to plant radishes 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). Radish needs 22–30 days to mature, which fits comfortably within Illinois's growing season.
When to plant radishes in Illinois: the short answer
For a spring planting, sow Mar 18 – Apr 6. Seeds germinate in soil from 40 to 85°F.
Succession sow again in Illinois: Apr 2 · Apr 12 · Apr 22 · May 2 · May 12 · May 22
Spring succession stops before summer heat makes it bolt. Start sowing again in late summer for a fall crop (see the fall window above).
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 radishes in Illinois, step by step
- Prepare the bed. They need six or more hours of sun for the best growth, though four to six hours in partial shade is enough and loose soil at least 6 inches deep, with a pH between 6.0 and 7.0. Dig in compost before planting.
- Sow outdoors (Mar 18 – Apr 6). Space plants about 2 inches apart in rows 6 inches apart, sowing seed ½ inch deep. It handles frost well, so it can go out before the last frost date. As a cool-season crop it does best before summer heat arrives in Illinois.
- Water and feed. Give it steady, even moisture, about an inch of water a week from rain or the hose.
- Watch for pests and problems. Pests: flea beetle, cabbage root maggot, aphids. Diseases and disorders: clubroot, scab, downy mildew.
- Harvest (from about Apr 14 – Apr 22). Radish takes 22-30 days to reach harvest. The classic marker crop and quick filler. Sow a short row every 10 days - a single big sowing all matures at once and then goes pithy and hot.
Figures come from our crop data; dates use Illinois’s average frost dates. More in the full radish growing guide.
Radish 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 radish dates shift with them.
When to plant radishes in nearby states
Questions gardeners in Illinois ask
When is the best time to plant radishes in Illinois?
Sow radishes in Illinois between March 18 and April 6. That timing is set by Illinois's average last spring frost of April 20.
Can I plant radishes in the fall in Illinois?
Yes. For a fall crop, sow between August 30 and September 16, so the crop matures in cool weather before Illinois's first frost around October 14.
When will radishes planted in Illinois be ready to harvest?
Planted on time, radishes are usually ready from about April 14 to April 22, 22-30 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.