When to plant onions in Indiana
Indiana’s average last spring frost is April 24, and the first fall frost typically arrives around October 11 — about 170 frost-free days (USDA zones 5b, 6a, 6b). Onion needs 90–120 days to mature, which fits comfortably within Indiana's growing season.
When to plant onions in Indiana: the short answer
For a spring planting, plant out Mar 27 – Apr 13, with seeds started indoors Feb 6 – Feb 20. Seeds germinate in soil from 40 to 90°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 onions in Indiana, step by step
- Start seeds indoors (Feb 6 – Feb 20). Sow seeds ½ inch deep in seed-starting mix under bright light. They take 7-14 days to sprout, fastest in soil around 70°F. Harden seedlings off for a week before they go outside.
- Prepare the bed. They need at least six to eight hours of direct sun a day and loose soil at least 12 inches deep, with a pH between 6.0 and 7.0. Dig in compost before planting.
- Plant out (Mar 27 – Apr 13). Space plants about 4 inches apart in rows 12 inches apart. 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 Indiana.
- 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: onion maggot, onion thrips. Diseases and disorders: downy mildew, white rot, neck rot, purple blotch.
- Harvest (from about Jul 2 – Aug 1). Onion takes 90-120 days to reach harvest. Match the day-length type to your latitude: long-day onions for the north, short-day for the south, day-neutral anywhere. Bulbing is triggered by day length, not calendar date.
Figures come from our crop data; dates use Indiana’s average frost dates. More in the full onion growing guide.
Onion planting dates by USDA zone in Indiana
Indiana spans USDA zones 5b, 6a, 6b. 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 onion dates shift with them.
When to plant onions in nearby states
Questions gardeners in Indiana ask
When is the best time to plant onions in Indiana?
Plant onion transplants outdoors in Indiana between March 27 and April 13. That timing is set by Indiana's average last spring frost of April 24.
When should I start onion seeds indoors in Indiana?
Start seeds indoors between February 6 and February 20, about 10 weeks before the last frost, so the seedlings are ready to plant out from March 27.
When will onions planted in Indiana be ready to harvest?
Planted on time, onions are usually ready from about July 2 to August 1, 90-120 days after transplanting.
When is the last frost in Indiana?
On average around April 24, with the first fall frost around October 11 - about 170 frost-free days. Your town may differ by two weeks or more.