When to plant onion in San Antonio
Onion is cold-hardy, so every date keys off San Antonio's frost dates of Feb 21.
Step 1 · Sow
Start seeds indoors
Dec 13 – Jan 3
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Jan 31 – Feb 21
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
May 1 – May 21
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
San Antonio's 282-day season leaves this much room.
Onion on San Antonio'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
FEB 21
NOV 29
Common questions
When will onion be ready to harvest in San Antonio?
Expect to harvest from around early May (May 1–May 21) in San Antonio, based on its local frost dates. Confidence 75%.
When should I start onion seeds indoors in San Antonio?
Start seeds indoors around mid December (Dec 13–Jan 3) in San Antonio, based on its local frost dates. Confidence 79%.
When can I transplant onion outdoors in San Antonio?
Transplant outdoors around late January (Jan 31–Feb 21) in San Antonio, based on its local frost dates. Confidence 83%.
How long is the growing season in San Antonio?
San Antonio has roughly 282 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 San Antonio's frost dates.
Confidence 83/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.