When to plant onion in Milwaukee
Onion is cold-hardy, so every date keys off Milwaukee's frost dates of Apr 23.
Step 1 · Sow
Start seeds indoors
Feb 12 – Mar 5
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
May 6 – May 27
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Aug 4 – Aug 24
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Milwaukee's 182-day season leaves this much room.
Onion on Milwaukee'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 23
OCT 23
Common questions
When will onion be ready to harvest in Milwaukee?
Expect to harvest from around early August (Aug 4–Aug 24) in Milwaukee, based on its local frost dates. Confidence 80%.
When should I start onion seeds indoors in Milwaukee?
Start seeds indoors around mid February (Feb 12–Mar 5) in Milwaukee, based on its local frost dates. Confidence 85%.
When can I transplant onion outdoors in Milwaukee?
Transplant outdoors around early May (May 6–May 27) in Milwaukee, based on its local frost dates. Confidence 86%.
How long is the growing season in Milwaukee?
Milwaukee has roughly 182 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 Milwaukee's frost dates.
Confidence 89/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.