When to plant onion in Montreal
Onion is cold-hardy, so every date keys off Montreal's frost dates of Apr 19.
Step 1 · Sow
Start seeds indoors
Feb 8 – Mar 1
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
May 10 – May 31
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Aug 8 – Aug 28
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Montreal's 192-day season leaves this much room.
Onion on Montreal'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 19
OCT 28
Common questions
When will onion be ready to harvest in Montreal?
Expect to harvest from around early August (Aug 8–Aug 28) in Montreal, based on its local frost dates. Confidence 76%.
When should I start onion seeds indoors in Montreal?
Start seeds indoors around early February (Feb 8–Mar 1) in Montreal, based on its local frost dates. Confidence 81%.
When can I transplant onion outdoors in Montreal?
Transplant outdoors around early May (May 10–May 31) in Montreal, based on its local frost dates. Confidence 82%.
How long is the growing season in Montreal?
Montreal has roughly 192 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 Montreal's frost dates.
Confidence 85/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.