When to plant onion in New Haven
Onion is cold-hardy, so every date keys off New Haven's frost dates of Apr 19.
Step 1 · Sow
Start seeds indoors
Feb 8 – Mar 1
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
New Haven's 184-day season leaves this much room.
Onion on New Haven'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 19
OCT 19
Common questions
When will onion be ready to harvest in New Haven?
Expect to harvest from around late July (Jul 24–Aug 13) in New Haven, based on its local frost dates. Confidence 75%.
When should I start onion seeds indoors in New Haven?
Start seeds indoors around early February (Feb 8–Mar 1) in New Haven, based on its local frost dates. Confidence 79%.
When can I transplant onion outdoors in New Haven?
Transplant outdoors around late April (Apr 25–May 16) in New Haven, based on its local frost dates. Confidence 81%.
How long is the growing season in New Haven?
New Haven has roughly 184 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 New Haven's frost dates.
Confidence 83/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.