When to plant onion in Glasgow
Onion is cold-hardy, so every date keys off Glasgow's frost dates of May 1.
Step 1 · Sow
Start seeds indoors
Feb 20 – Mar 13
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
May 20 – Jun 10
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Aug 18 – Sep 7
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Glasgow's 183-day season leaves this much room.
Onion on Glasgow'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 1
OCT 27
Common questions
When will onion be ready to harvest in Glasgow?
Expect to harvest from around mid August (Aug 18–Sep 7) in Glasgow, based on its local frost dates. Confidence 74%.
When should I start onion seeds indoors in Glasgow?
Start seeds indoors around mid February (Feb 20–Mar 13) in Glasgow, based on its local frost dates. Confidence 78%.
When can I transplant onion outdoors in Glasgow?
Transplant outdoors around mid May (May 20–Jun 10) in Glasgow, based on its local frost dates. Confidence 80%.
How long is the growing season in Glasgow?
Glasgow has roughly 183 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 Glasgow's frost dates.
Confidence 82/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.