When to plant onion in Tacoma
Onion is cold-hardy, so every date keys off Tacoma's frost dates of Mar 8.
Step 1 · Sow
Start seeds indoors
Dec 28 – Jan 18
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Apr 9 – Apr 30
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Jul 8 – Jul 28
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Tacoma's 246-day season leaves this much room.
Onion on Tacoma'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 8
NOV 13
Common questions
When will onion be ready to harvest in Tacoma?
Expect to harvest from around early July (Jul 8–Jul 28) in Tacoma, based on its local frost dates. Confidence 76%.
When should I start onion seeds indoors in Tacoma?
Start seeds indoors around late December (Dec 28–Jan 18) in Tacoma, based on its local frost dates. Confidence 81%.
When can I transplant onion outdoors in Tacoma?
Transplant outdoors around early April (Apr 9–Apr 30) in Tacoma, based on its local frost dates. Confidence 82%.
How long is the growing season in Tacoma?
Tacoma has roughly 246 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 Tacoma's frost dates.
Confidence 85/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.