When to plant onions in South Carolina
South Carolina’s average last spring frost is March 25, and the first fall frost typically arrives around November 5 — about 225 frost-free days (USDA zones 7a, 7b, 8a, 8b, 9a). Onion needs 90–120 days to mature, which fits comfortably within South Carolina's growing season.
When to plant onions in South Carolina: the short answer
For a spring planting, plant out Feb 25 – Mar 14, with seeds started indoors Jan 7 – Jan 21. 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 South Carolina, step by step
- Start seeds indoors (Jan 7 – Jan 21). 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 (Feb 25 – Mar 14). 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 South Carolina.
- 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 2 – Jul 2). 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 South Carolina’s average frost dates. More in the full onion growing guide.
Onion planting dates by USDA zone in South Carolina
South Carolina spans USDA zones 7a, 7b, 8a, 8b, 9a. 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 |
|---|---|---|
| South Carolina (this page) | March 25 | Feb 25 – Mar 14 |
| North Carolina | April 5 | Mar 8 – Mar 25 |
| Georgia | March 25 | Feb 25 – Mar 14 |
| Tennessee | April 10 | Mar 13 – Mar 30 |
| Kentucky | April 18 | Mar 21 – Apr 7 |
Questions gardeners in South Carolina ask
When is the best time to plant onions in South Carolina?
Plant onion transplants outdoors in South Carolina between February 25 and March 14. That timing is set by South Carolina's average last spring frost of March 25.
When should I start onion seeds indoors in South Carolina?
Start seeds indoors between January 7 and January 21, about 10 weeks before the last frost, so the seedlings are ready to plant out from February 25.
When will onions planted in South Carolina be ready to harvest?
Planted on time, onions are usually ready from about June 2 to July 2, 90-120 days after transplanting.
When is the last frost in South Carolina?
On average around March 25, with the first fall frost around November 5 - about 225 frost-free days. Your town may differ by two weeks or more.