When to plant radishes in Iowa
Iowa’s average last spring frost is April 25, and the first fall frost typically arrives around October 8 — about 166 frost-free days (USDA zones 4b, 5a, 5b). Radish needs 22–30 days to mature, which fits comfortably within Iowa's growing season.
When to plant radishes in Iowa: the short answer
For a spring planting, sow Mar 23 – Apr 11. Seeds germinate in soil from 40 to 85°F.
Succession sow again in Iowa: Apr 7 · Apr 17 · Apr 27 · May 7 · May 17 · May 27
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 Iowa, 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 23 – Apr 11). 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 Iowa.
- 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 19 – Apr 27). 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 Iowa’s average frost dates. More in the full radish growing guide.
Radish planting dates by USDA zone in Iowa
Iowa spans USDA zones 4b, 5a, 5b. 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 Iowa ask
When is the best time to plant radishes in Iowa?
Sow radishes in Iowa between March 23 and April 11. That timing is set by Iowa's average last spring frost of April 25.
Can I plant radishes in the fall in Iowa?
Yes. For a fall crop, sow between August 24 and September 10, so the crop matures in cool weather before Iowa's first frost around October 8.
When will radishes planted in Iowa be ready to harvest?
Planted on time, radishes are usually ready from about April 19 to April 27, 22-30 days after sowing.
When is the last frost in Iowa?
On average around April 25, with the first fall frost around October 8 - about 166 frost-free days. Your town may differ by two weeks or more.