When to plant zucchini / summer squash 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). Zucchini / Summer Squash needs 45–60 days to mature, which fits comfortably within Iowa's growing season.
When to plant zucchini / summer squash in Iowa: the short answer
For a spring planting, plant out Apr 25 – May 12, with seeds started indoors Mar 28 – Apr 11. Wait until the soil is at least 60°F and frost is over.
Succession sow again in Iowa: May 30 · Jun 27 · Jul 25
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 Iowa, step by step
- Start seeds indoors (Mar 28 – Apr 11). 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 25 – May 12). 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 16 – Jul 1). 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 Iowa’s average frost dates. More in the full zucchini / summer squash growing guide.
Zucchini 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 zucchini / summer squash dates shift with them.
When to plant zucchini / summer squash in nearby states
Questions gardeners in Iowa ask
When is the best time to plant zucchini / summer squash in Iowa?
Plant zucchini / summer squash transplants outdoors in Iowa between April 25 and May 12. That timing is set by Iowa's average last spring frost of April 25.
When should I start zucchini / summer squash seeds indoors in Iowa?
Start seeds indoors between March 28 and April 11, about 3 weeks before the last frost, so the seedlings are ready to plant out from April 25.
Can I plant zucchini / summer squash in the fall in Iowa?
Yes. For a fall crop, sow between July 6 and July 23, so the crop matures in cool weather before Iowa's first frost around October 8.
When will zucchini / summer squash planted in Iowa be ready to harvest?
Planted on time, zucchini / summer squash is usually ready from about June 16 to July 1, 45-60 days after planting.
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.