When to plant onion in Cologne
Onion is cold-hardy, so every date keys off Cologne's frost dates of Apr 20.
Step 1 · Sow
Start seeds indoors
Feb 9 – Mar 2
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Mar 30 – Apr 20
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Jun 28 – Jul 18
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Cologne's 185-day season leaves this much room.
Onion on Cologne'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
APR 20
OCT 22
Common questions
When will onion be ready to harvest in Cologne?
Expect to harvest from around late June (Jun 28–Jul 18) in Cologne, based on its local frost dates. Confidence 74%.
When should I start onion seeds indoors in Cologne?
Start seeds indoors around early February (Feb 9–Mar 2) in Cologne, based on its local frost dates. Confidence 78%.
When can I transplant onion outdoors in Cologne?
Transplant outdoors around late March (Mar 30–Apr 20) in Cologne, based on its local frost dates. Confidence 82%.
How long is the growing season in Cologne?
Cologne has roughly 185 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 Cologne's frost dates.
Confidence 82/100 · NOAA GHCN-Daily · 1991–2020 normals · frost dates are probabilities, not guarantees.