When to plant onion in Modesto
Onion is cold-hardy, so every date keys off Modesto's frost dates of Jan 27.
Step 1 · Sow
Start seeds indoors
Nov 18 – Dec 9
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Feb 10 – Mar 3
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
May 11 – May 31
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Modesto's 310-day season leaves this much room.
Onion on Modesto'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
JAN 27
DEC 3
Common questions
When will onion be ready to harvest in Modesto?
Expect to harvest from around mid May (May 11–May 31) in Modesto, based on its local frost dates. Confidence 78%.
When should I start onion seeds indoors in Modesto?
Start seeds indoors around mid November (Nov 18–Dec 9) in Modesto, based on its local frost dates. Confidence 83%.
When can I transplant onion outdoors in Modesto?
Transplant outdoors around early February (Feb 10–Mar 3) in Modesto, based on its local frost dates. Confidence 84%.
How long is the growing season in Modesto?
Modesto has roughly 310 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 Modesto's frost dates.
Confidence 87/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.