When to plant onion in Bristol
Onion is cold-hardy, so every date keys off Bristol's frost dates of Apr 18.
Step 1 · Sow
Start seeds indoors
Feb 7 – Feb 28
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Mar 28 – Apr 18
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Jun 26 – Jul 16
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Bristol's 197-day season leaves this much room.
Onion on Bristol'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 18
NOV 1
Common questions
When will onion be ready to harvest in Bristol?
Expect to harvest from around late June (Jun 26–Jul 16) in Bristol, based on its local frost dates. Confidence 74%.
When should I start onion seeds indoors in Bristol?
Start seeds indoors around early February (Feb 7–Feb 28) in Bristol, based on its local frost dates. Confidence 78%.
When can I transplant onion outdoors in Bristol?
Transplant outdoors around late March (Mar 28–Apr 18) in Bristol, based on its local frost dates. Confidence 82%.
How long is the growing season in Bristol?
Bristol has roughly 197 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 Bristol's frost dates.
Confidence 82/100 · NOAA GHCN-Daily · 1991–2020 normals · frost dates are probabilities, not guarantees.