When to plant onion in Duluth
Onion is cold-hardy, so every date keys off Duluth's frost dates of May 10.
Step 1 · Sow
Start seeds indoors
Mar 1 – Mar 22
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
May 30 – Jun 20
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Aug 28 – Sep 17
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Duluth's 150-day season leaves this much room.
Onion on Duluth'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
MAY 10
OCT 7
Common questions
When will onion be ready to harvest in Duluth?
Expect to harvest from around late August (Aug 28–Sep 17) in Duluth, based on its local frost dates. Confidence 78%.
When should I start onion seeds indoors in Duluth?
Start seeds indoors around early March (Mar 1–Mar 22) in Duluth, based on its local frost dates. Confidence 83%.
When can I transplant onion outdoors in Duluth?
Transplant outdoors around late May (May 30–Jun 20) in Duluth, based on its local frost dates. Confidence 84%.
How long is the growing season in Duluth?
Duluth has roughly 150 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 Duluth's frost dates.
Confidence 87/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.