When to plant onion in Birmingham
Onion is cold-hardy, so every date keys off Birmingham's frost dates of Apr 17.
Step 1 · Sow
Start seeds indoors
Feb 6 – Feb 27
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
May 2 – May 23
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Jul 31 – Aug 20
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Birmingham's 204-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
APR 17
NOV 7
Common questions
When will onion be ready to harvest in Birmingham?
Expect to harvest from around late July (Jul 31–Aug 20) in Birmingham, based on its local frost dates. Confidence 79%.
When should I start onion seeds indoors in Birmingham?
Start seeds indoors around early February (Feb 6–Feb 27) in Birmingham, based on its local frost dates. Confidence 84%.
When can I transplant onion outdoors in Birmingham?
Transplant outdoors around early May (May 2–May 23) in Birmingham, based on its local frost dates. Confidence 85%.
How long is the growing season in Birmingham?
Birmingham has roughly 204 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 88/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.