When to plant onion in Sapporo
Onion is cold-hardy, so every date keys off Sapporo's frost dates of May 12.
Step 1 · Sow
Start seeds indoors
Mar 3 – Mar 24
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
May 26 – Jun 16
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Aug 24 – Sep 13
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Sapporo's 166-day season leaves this much room.
Onion on Sapporo'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
MAY 12
OCT 20
Common questions
When will onion be ready to harvest in Sapporo?
Expect to harvest from around late August (Aug 24–Sep 13) in Sapporo, based on its local frost dates. Confidence 40%.
When should I start onion seeds indoors in Sapporo?
Start seeds indoors around early March (Mar 3–Mar 24) in Sapporo, based on its local frost dates. Confidence 43%.
When can I transplant onion outdoors in Sapporo?
Transplant outdoors around late May (May 26–Jun 16) in Sapporo, based on its local frost dates. Confidence 44%.
How long is the growing season in Sapporo?
Sapporo has roughly 166 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 Sapporo's frost dates.
Confidence 45/100 · Curated · based on NASA POWER (modeled) 1991–2020 · frost dates are probabilities, not guarantees.