When to plant onion in Charleston
Onion is cold-hardy, so every date keys off Charleston's frost dates of Feb 8.
Step 1 · Sow
Start seeds indoors
Nov 30 – Dec 21
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Jan 20 – Feb 10
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Apr 20 – May 10
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Charleston's 310-day season leaves this much room.
Onion on Charleston's growing year
Frost-bounded season with crops mapped onto the 12-month axis.
Frost risk Growing Harvest
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
NOV
DEC
FROST
FEB 8
DEC 15
Common questions
When will onion be ready to harvest in Charleston?
Expect to harvest from around mid April (Apr 20–May 10) in Charleston, based on its local frost dates. Confidence 80%.
When should I start onion seeds indoors in Charleston?
Start seeds indoors around late November (Nov 30–Dec 21) in Charleston, based on its local frost dates. Confidence 85%.
When can I transplant onion outdoors in Charleston?
Transplant outdoors around mid January (Jan 20–Feb 10) in Charleston, based on its local frost dates. Confidence 86%.
How long is the growing season in Charleston?
Charleston has roughly 310 frost-free days, which is enough time to grow onion to maturity outdoors.
The rule of thumb
Sow onion as soon as the soil is workable — it tolerates cool weather and light frost. Every date on this page is derived from that rule and Charleston's frost dates.
Confidence 89/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.