When to plant onion in Cincinnati
Onion is cold-hardy, so every date keys off Cincinnati's frost dates of Apr 13.
Step 1 · Sow
Start seeds indoors
Feb 2 – Feb 23
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Apr 12 – May 3
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Jul 11 – Jul 31
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Cincinnati's 194-day season leaves this much room.
Onion on Cincinnati'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 13
OCT 22
Common questions
When will onion be ready to harvest in Cincinnati?
Expect to harvest from around mid July (Jul 11–Jul 31) in Cincinnati, based on its local frost dates. Confidence 79%.
When should I start onion seeds indoors in Cincinnati?
Start seeds indoors around early February (Feb 2–Feb 23) in Cincinnati, based on its local frost dates. Confidence 84%.
When can I transplant onion outdoors in Cincinnati?
Transplant outdoors around mid April (Apr 12–May 3) in Cincinnati, based on its local frost dates. Confidence 85%.
How long is the growing season in Cincinnati?
Cincinnati has roughly 194 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 Cincinnati's frost dates.
Confidence 88/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.