When to plant onion in Birmingham
Onion is cold-hardy, so every date keys off Birmingham's frost dates of Mar 27.
Step 1 · Sow
Start seeds indoors
Jan 16 – Feb 6
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Mar 6 – Mar 27
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Jun 4 – Jun 24
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Birmingham's 229-day season leaves this much room.
Onion on Birmingham'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
MAR 27
NOV 11
Common questions
When will onion be ready to harvest in Birmingham?
Expect to harvest from around early June (Jun 4–Jun 24) in Birmingham, based on its local frost dates. Confidence 80%.
When should I start onion seeds indoors in Birmingham?
Start seeds indoors around mid January (Jan 16–Feb 6) in Birmingham, based on its local frost dates. Confidence 85%.
When can I transplant onion outdoors in Birmingham?
Transplant outdoors around early March (Mar 6–Mar 27) in Birmingham, based on its local frost dates. Confidence 89%.
How long is the growing season in Birmingham?
Birmingham has roughly 229 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 Birmingham's frost dates.
Confidence 89/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.