When to plant broccoli 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). Broccoli needs 60–85 days to mature, which fits comfortably within Illinois's growing season.
When to plant broccoli in Illinois: the short answer
For a spring planting, plant out Mar 30 – Apr 16, with seeds started indoors Mar 2 – Mar 16. Seeds germinate in soil from 45 to 85°F.
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 broccoli in Illinois, step by step
- Start seeds indoors (Mar 2 – Mar 16). Sow seeds ½ inch deep in seed-starting mix under bright light. They take 5-10 days to sprout, fastest in soil around 75°F. Harden seedlings off for a week before they go outside.
- Prepare the bed. It needs at least six to eight hours of direct sun a day and loose soil at least 18 inches deep, with a pH between 6.0 and 7.0. Dig in compost before planting.
- Plant out (Mar 30 – Apr 16). Space plants about 18 inches apart in rows 30 inches apart. It tolerates a light frost but not a hard freeze. 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: cabbage worm, cabbage looper, aphids, flea beetle, cabbage root maggot. Diseases and disorders: clubroot, black rot, downy mildew.
- Harvest (from about Jun 5 – Jun 30). Broccoli takes 60-85 days to reach harvest. Days to maturity counted from transplant. Keep cutting side shoots after the main head for weeks. Spring crop must size up before heat or it buttons.
Figures come from our crop data; dates use Illinois’s average frost dates. More in the full broccoli growing guide.
Broccoli 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 broccoli dates shift with them.
When to plant broccoli in nearby states
Questions gardeners in Illinois ask
When is the best time to plant broccoli in Illinois?
Plant broccoli transplants outdoors in Illinois between March 30 and April 16. That timing is set by Illinois's average last spring frost of April 20.
When should I start broccoli seeds indoors in Illinois?
Start seeds indoors between March 2 and March 16, about 6 weeks before the last frost, so the seedlings are ready to plant out from March 30.
Can I plant broccoli in the fall in Illinois?
Yes. For a fall crop, start transplants between July 5 and July 22, so the crop matures in cool weather before Illinois's first frost around October 14.
When will broccoli planted in Illinois be ready to harvest?
Planted on time, broccoli is usually ready from about June 5 to June 30, 60-85 days after transplanting.
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.