When to plant zucchini / summer squash 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). Zucchini / Summer Squash needs 45–60 days to mature, which fits comfortably within Illinois's growing season.
When to plant zucchini / summer squash in Illinois: the short answer
For a spring planting, plant out Apr 20 – May 7, with seeds started indoors Mar 23 – Apr 6. Wait until the soil is at least 60°F and frost is over.
Succession sow again in Illinois: May 25 · Jun 22 · 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 zucchini / summer squash in Illinois, step by step
- Start seeds indoors (Mar 23 – Apr 6). Sow seeds 1 inch deep in seed-starting mix under bright light. They take 5-10 days to sprout, fastest in soil around 85°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 14 inches deep, with a pH between 5.5 and 7.5. Dig in compost before planting.
- Plant out (Apr 20 – May 7). Space plants about 30 inches apart in rows 42 inches apart. It is killed by frost, so nothing goes outside until the danger has passed.
- 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: squash vine borer, squash bug, striped cucumber beetle, aphids. Diseases and disorders: powdery mildew, bacterial wilt, blossom-end rot (calcium disorder).
- Harvest (from about Jun 11 – Jun 26). Zucchini / Summer Squash takes 45-60 days to reach harvest. One or two plants feed a household. A second sowing in early-mid summer dodges the first vine borer generation.
Figures come from our crop data; dates use Illinois’s average frost dates. More in the full zucchini / summer squash growing guide.
Zucchini 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 zucchini / summer squash dates shift with them.
When to plant zucchini / summer squash in nearby states
Questions gardeners in Illinois ask
When is the best time to plant zucchini / summer squash in Illinois?
Plant zucchini / summer squash transplants outdoors in Illinois between April 20 and May 7. That timing is set by Illinois's average last spring frost of April 20.
When should I start zucchini / summer squash seeds indoors in Illinois?
Start seeds indoors between March 23 and April 6, about 3 weeks before the last frost, so the seedlings are ready to plant out from April 20.
Can I plant zucchini / summer squash in the fall in Illinois?
Yes. For a fall crop, sow between July 12 and July 29, so the crop matures in cool weather before Illinois's first frost around October 14.
When will zucchini / summer squash planted in Illinois be ready to harvest?
Planted on time, zucchini / summer squash is usually ready from about June 11 to June 26, 45-60 days after planting.
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.