When to plant onion in Tokyo
Onion is cold-hardy, so every date keys off Tokyo's frost dates of Mar 28.
Step 1 · Sow
Start seeds indoors
Jan 17 – Feb 7
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Mar 29 – Apr 19
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Jun 27 – Jul 17
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Tokyo's 258-day season leaves this much room.
Onion on Tokyo'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 28
DEC 11
Common questions
When will onion be ready to harvest in Tokyo?
Expect to harvest from around late June (Jun 27–Jul 17) in Tokyo, based on its local frost dates. Confidence 40%.
When should I start onion seeds indoors in Tokyo?
Start seeds indoors around mid January (Jan 17–Feb 7) in Tokyo, based on its local frost dates. Confidence 43%.
When can I transplant onion outdoors in Tokyo?
Transplant outdoors around late March (Mar 29–Apr 19) in Tokyo, based on its local frost dates. Confidence 44%.
How long is the growing season in Tokyo?
Tokyo 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 Tokyo's frost dates.
Confidence 45/100 · Curated · based on NASA POWER (modeled) 1991–2020 · frost dates are probabilities, not guarantees.