When to plant onion in Osaka
Onion is cold-hardy, so every date keys off Osaka's frost dates of Mar 22.
Step 1 · Sow
Start seeds indoors
Jan 11 – Feb 1
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Mar 1 – Mar 22
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
May 30 – Jun 19
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Osaka's 258-day season leaves this much room.
Onion on Osaka'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
MAR 22
DEC 5
Common questions
When will onion be ready to harvest in Osaka?
Expect to harvest from around late May (May 30–Jun 19) in Osaka, based on its local frost dates. Confidence 77%.
When should I start onion seeds indoors in Osaka?
Start seeds indoors around mid January (Jan 11–Feb 1) in Osaka, based on its local frost dates. Confidence 82%.
When can I transplant onion outdoors in Osaka?
Transplant outdoors around early March (Mar 1–Mar 22) in Osaka, based on its local frost dates. Confidence 86%.
How long is the growing season in Osaka?
Osaka has roughly 258 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 Osaka's frost dates.
Confidence 86/100 · NOAA GHCN-Daily · 1991–2020 normals · frost dates are probabilities, not guarantees.