When to plant onion in Tucson
Onion is cold-hardy, so every date keys off Tucson's frost dates of Feb 27.
Step 1 · Sow
Start seeds indoors
Dec 19 – Jan 9
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Dec 26 – Jan 16
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Mar 26 – Apr 15
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Tucson's 278-day season leaves this much room.
Onion on Tucson'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 27
NOV 27
Common questions
When will onion be ready to harvest in Tucson?
Expect to harvest from around late March (Mar 26–Apr 15) in Tucson, based on its local frost dates. Confidence 75%.
When should I start onion seeds indoors in Tucson?
Start seeds indoors around mid December (Dec 19–Jan 9) in Tucson, based on its local frost dates. Confidence 79%.
When can I transplant onion outdoors in Tucson?
Transplant outdoors around late December (Dec 26–Jan 16) in Tucson, based on its local frost dates. Confidence 81%.
How long is the growing season in Tucson?
Tucson has roughly 278 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 Tucson's frost dates.
Confidence 83/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.