When to plant onion in Columbia
Onion is cold-hardy, so every date keys off Columbia's frost dates of Mar 11.
Step 1 · Sow
Start seeds indoors
Dec 31 – Jan 21
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Feb 18 – Mar 11
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
May 19 – Jun 8
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Columbia's 248-day season leaves this much room.
Onion on Columbia'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
FROST
MAR 11
NOV 17
Common questions
When will onion be ready to harvest in Columbia?
Expect to harvest from around mid May (May 19–Jun 8) in Columbia, based on its local frost dates. Confidence 79%.
When should I start onion seeds indoors in Columbia?
Start seeds indoors around late December (Dec 31–Jan 21) in Columbia, based on its local frost dates. Confidence 84%.
When can I transplant onion outdoors in Columbia?
Transplant outdoors around mid February (Feb 18–Mar 11) in Columbia, based on its local frost dates. Confidence 88%.
How long is the growing season in Columbia?
Columbia has roughly 248 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 Columbia's frost dates.
Confidence 88/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.