South Carolina planting calendar

When to plant onions in South Carolina — sow, transplant & harvest dates

South Carolina is mostly USDA zone 8a (range 7a-9a). Dates below are derived from onions's frost tolerance and South Carolina's frost window — not generic national averages.

Onions planting timetable for South Carolina

Stage	When in South Carolina	Anchor
Start seeds indoors	mid-January (January 14)	10 weeks before the last frost (late March)
Transplant outside	late February (February 25)	28 days before the last frost (late March)
First harvest (estimate)	mid-June (June 15)	~110 days from transplant

Dates are state-wide averages for the dominant zone. Local microclimates — elevation, urban heat, coastal moderation — can shift the window by 1-2 weeks. Use the frost-date calculator for a date tuned to your town.

Why South Carolina's climate shifts the onions dates

South Carolina's last spring frost averages late March and first fall frost early November, which sets the whole planting clock. South Carolina has a long, hot, humid season with mild winters. The coast is nearly frost-free; the upstate sees a brief cold spell. Sow early — onions bolt once daytime temperatures hold above 24 °C, so the earlier they go in, the longer the harvest.

Onions are day-length sensitive: long-day varieties (zones 1–6) begin bulbing when days exceed 14 hours, short-day types (zones 7–10) bulb at 10–12 hours, and intermediate-day varieties span zones 5–6. Start seeds indoors 10–12 weeks before the last spring frost and transplant out 4–6 weeks before it — young onion seedlings tolerate frost down to about -6 °C once hardened off. In zones 8–10 a second planting from sets in autumn is common, overwintering for an early-summer harvest.

Frost-risk note

Don't plant before late March — a hard freeze can still set young plants back. In the Blue Ridge upstate near the mountains (zone 7a) the safe date runs a week or two later.

Regional variation within South Carolina

the Blue Ridge upstate near the mountains (zone 7a) runs roughly 1-2 weeks behind the state average; the Lowcountry coast around Charleston (zone 9a) can plant 1-2 weeks earlier.

Columbia — USDA zone 8b
Charleston — USDA zone 9a
Greenville — USDA zone 8a
Myrtle Beach — USDA zone 8b

What else to plant in South Carolina around then

The same early window suits peas, lettuce, spinach, and onion sets.

Quick-grow guide

Sun: Full sun — 6+ hours direct.
Soil temperature for germination: 10-35 °C (50-95 °F).
Spacing: 4-6 inches (10-15 cm) between plants.
Days to harvest: ~110 days from planting out.

Frequently asked questions

When is the best time to plant onions in South Carolina?

In South Carolina (mostly USDA zone 8a), sow onions indoors around mid-January, transplant outdoors late February (before the last frost, late March), and harvest from mid-June. Onions are cold-hardy — they tolerate frost and actively prefer cool weather, so they go in well before the last spring frost and bolt in summer heat.

What USDA zone is South Carolina?

Most of South Carolina sits in USDA hardiness zone 8a, with the state spanning roughly 7a-9a from the Blue Ridge upstate near the mountains (zone 7a) to the Lowcountry coast around Charleston (zone 9a). The last spring frost averages late March and the first fall frost early November.

Can you grow onions in South Carolina?

Yes. South Carolina's dominant zone 8a supports onions — the key is timing. Onions are cold-hardy — they tolerate frost and actively prefer cool weather, so they go in well before the last spring frost and bolt in summer heat.

Does the planting date change across South Carolina?

the Blue Ridge upstate near the mountains (zone 7a) runs roughly 1-2 weeks behind the state average; the Lowcountry coast around Charleston (zone 9a) can plant 1-2 weeks earlier.

What else can I plant in South Carolina around the same time?

The same early window suits peas, lettuce, spinach, and onion sets.

Source and methodology

State zone spans from the USDA Plant Hardiness Zone Map (2023); frost-date averages from NOAA Climate Data Online. Hot-state two-season timing cross-checked against the UF/IFAS Florida Gardening Calendar and the University of Arizona Cooperative Extension planting calendar. Curated by the Growli editorial team.