When to plant onion in Montreal
Onion is cold-hardy, so every date keys off Montreal's frost dates of May 11.
Step 1 · Sow
Start seeds indoors
Mar 2 – Mar 23
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Apr 20 – May 11
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Jul 19 – Aug 8
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Montreal's 142-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
MAY 11
SEP 30
Common questions
When will onion be ready to harvest in Montreal?
Expect to harvest from around mid July (Jul 19–Aug 8) in Montreal, based on its local frost dates. Confidence 77%.
When should I start onion seeds indoors in Montreal?
Start seeds indoors around early March (Mar 2–Mar 23) in Montreal, based on its local frost dates. Confidence 82%.
When can I transplant onion outdoors in Montreal?
Transplant outdoors around mid April (Apr 20–May 11) in Montreal, based on its local frost dates. Confidence 86%.
How long is the growing season in Montreal?
Montreal has roughly 142 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 86/100 · NOAA GHCN-Daily · 1991–2020 normals · frost dates are probabilities, not guarantees.