When to plant onion in Detroit
Onion is cold-hardy, so every date keys off Detroit's frost dates of Apr 15.
Step 1 · Sow
Start seeds indoors
Feb 4 – Feb 25
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Apr 25 – May 16
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Jul 24 – Aug 13
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Detroit's 194-day season leaves this much room.
Onion on Detroit'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 15
OCT 31
Common questions
When will onion be ready to harvest in Detroit?
Expect to harvest from around late July (Jul 24–Aug 13) in Detroit, based on its local frost dates. Confidence 79%.
When should I start onion seeds indoors in Detroit?
Start seeds indoors around early February (Feb 4–Feb 25) in Detroit, based on its local frost dates. Confidence 84%.
When can I transplant onion outdoors in Detroit?
Transplant outdoors around late April (Apr 25–May 16) in Detroit, based on its local frost dates. Confidence 85%.
How long is the growing season in Detroit?
Detroit 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 Detroit's frost dates.
Confidence 88/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.