When to plant onion in Louisville
Onion is cold-hardy, so every date keys off Louisville's frost dates of Apr 1.
Step 1 · Sow
Start seeds indoors
Jan 21 – Feb 11
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Mar 29 – Apr 19
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Jun 27 – Jul 17
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Louisville's 212-day season leaves this much room.
Onion on Louisville'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 1
OCT 29
Common questions
When will onion be ready to harvest in Louisville?
Expect to harvest from around late June (Jun 27–Jul 17) in Louisville, based on its local frost dates. Confidence 74%.
When should I start onion seeds indoors in Louisville?
Start seeds indoors around late January (Jan 21–Feb 11) in Louisville, based on its local frost dates. Confidence 78%.
When can I transplant onion outdoors in Louisville?
Transplant outdoors around late March (Mar 29–Apr 19) in Louisville, based on its local frost dates. Confidence 80%.
How long is the growing season in Louisville?
Louisville has roughly 212 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 Louisville's frost dates.
Confidence 82/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.