When to plant basil 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). Basil needs 30–60 days to mature, which fits comfortably within Iowa's growing season.
When to plant basil in Iowa: the short answer
For a spring planting, plant out May 2 – May 19, with seeds started indoors Mar 14 – Mar 28. Wait until the soil is at least 65°F and frost is over.
Succession sow again in Iowa: May 30 · Jun 20 · Jul 11 · Aug 1 · Aug 22
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 basil in Iowa, step by step
- Start seeds indoors (Mar 14 – Mar 28). Sow seeds ⅛ inch deep in seed-starting mix under bright light. They take 5-10 days to sprout, fastest in soil around 80°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 10 inches deep, with a pH between 6.0 and 7.0. Dig in compost before planting.
- Plant out (May 2 – May 19). Space plants about 10 inches apart in rows 12 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: aphids, Japanese beetle, slugs. Diseases and disorders: basil downy mildew, fusarium wilt, damping off.
- Harvest (from about Jun 8 – Jul 8). Basil takes 30-60 days to reach harvest. Cold soil stalls it - wait for warm nights. Pinch above a leaf pair every couple of weeks and remove flower buds to keep leaves coming. Downy mildew-resistant varieties are worth seeking out.
Figures come from our crop data; dates use Iowa’s average frost dates. More in the full basil growing guide.
Basil 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 basil dates shift with them.
When to plant basil in nearby states
Questions gardeners in Iowa ask
When is the best time to plant basil in Iowa?
Plant basil transplants outdoors in Iowa between May 2 and May 19. That timing is set by Iowa's average last spring frost of April 25.
When should I start basil seeds indoors in Iowa?
Start seeds indoors between March 14 and March 28, about 5 weeks before the last frost, so the seedlings are ready to plant out from May 2.
What is the latest I can plant basil in Iowa?
About September 8. Basil needs at least 30 days to mature, and frost around October 8 ends the season, so later plantings risk being cut short.
When will basil planted in Iowa be ready to harvest?
Planted on time, basil is usually ready from about June 8 to July 8, 30-60 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.