When to plant onion in Birmingham
Onion is cold-hardy, so every date keys off Birmingham's frost dates of Apr 24.
Step 1 · Sow
Start seeds indoors
Feb 13 – Mar 6
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Apr 3 – Apr 24
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Jul 2 – Jul 22
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Birmingham's 181-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 24
OCT 22
Common questions
When will onion be ready to harvest in Birmingham?
Expect to harvest from around early July (Jul 2–Jul 22) in Birmingham, based on its local frost dates. Confidence 76%.
When should I start onion seeds indoors in Birmingham?
Start seeds indoors around mid February (Feb 13–Mar 6) in Birmingham, based on its local frost dates. Confidence 80%.
When can I transplant onion outdoors in Birmingham?
Transplant outdoors around early April (Apr 3–Apr 24) in Birmingham, based on its local frost dates. Confidence 84%.
How long is the growing season in Birmingham?
Birmingham has roughly 181 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 84/100 · NOAA GHCN-Daily · 1991–2020 normals · frost dates are probabilities, not guarantees.