When to plant onion in Baltimore
Onion is cold-hardy, so every date keys off Baltimore's frost dates of Mar 21.
Step 1 · Sow
Start seeds indoors
Jan 10 – Jan 31
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Apr 7 – Apr 28
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Jul 6 – Jul 26
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Baltimore's 249-day season leaves this much room.
Onion on Baltimore'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
MAR 21
NOV 27
Common questions
When will onion be ready to harvest in Baltimore?
Expect to harvest from around early July (Jul 6–Jul 26) in Baltimore, based on its local frost dates. Confidence 76%.
When should I start onion seeds indoors in Baltimore?
Start seeds indoors around early January (Jan 10–Jan 31) in Baltimore, based on its local frost dates. Confidence 80%.
When can I transplant onion outdoors in Baltimore?
Transplant outdoors around early April (Apr 7–Apr 28) in Baltimore, based on its local frost dates. Confidence 81%.
How long is the growing season in Baltimore?
Baltimore has roughly 249 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 Baltimore's frost dates.
Confidence 84/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.