When to plant onions in Kentucky
Kentucky’s average last spring frost is April 18, and the first fall frost typically arrives around October 20 — about 185 frost-free days (USDA zones 6a, 6b, 7a). Onion needs 90–120 days to mature, which fits comfortably within Kentucky's growing season.
When to plant onions in Kentucky: the short answer
For a spring planting, plant out Mar 21 – Apr 7, with seeds started indoors Jan 31 – Feb 14. 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 Kentucky, step by step
- Start seeds indoors (Jan 31 – Feb 14). 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 21 – Apr 7). 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 Kentucky.
- 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 Jun 26 – Jul 26). 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 Kentucky’s average frost dates. More in the full onion growing guide.
Onion planting dates by USDA zone in Kentucky
Kentucky spans USDA zones 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 onion dates shift with them.
When to plant onions in nearby states
| State | Last frost | Plant out |
|---|---|---|
| Kentucky (this page) | April 18 | Mar 21 – Apr 7 |
| North Carolina | April 5 | Mar 8 – Mar 25 |
| South Carolina | March 25 | Feb 25 – Mar 14 |
| Georgia | March 25 | Feb 25 – Mar 14 |
| Tennessee | April 10 | Mar 13 – Mar 30 |
Questions gardeners in Kentucky ask
When is the best time to plant onions in Kentucky?
Plant onion transplants outdoors in Kentucky between March 21 and April 7. That timing is set by Kentucky's average last spring frost of April 18.
When should I start onion seeds indoors in Kentucky?
Start seeds indoors between January 31 and February 14, about 10 weeks before the last frost, so the seedlings are ready to plant out from March 21.
When will onions planted in Kentucky be ready to harvest?
Planted on time, onions are usually ready from about June 26 to July 26, 90-120 days after transplanting.
When is the last frost in Kentucky?
On average around April 18, with the first fall frost around October 20 - about 185 frost-free days. Your town may differ by two weeks or more.