When to plant onion in Billings
Onion is cold-hardy, so every date keys off Billings's frost dates of May 8.
Step 1 · Sow
Start seeds indoors
Feb 27 – Mar 20
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Apr 28 – May 19
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Jul 27 – Aug 16
Picking runs until conditions turn against the crop.
Window
Days to maturity
90 – 110 d
Billings's 150-day season leaves this much room.
Onion on Billings'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
MAY 8
OCT 4
Common questions
When will onion be ready to harvest in Billings?
Expect to harvest from around late July (Jul 27–Aug 16) in Billings, based on its local frost dates. Confidence 81%.
When should I start onion seeds indoors in Billings?
Start seeds indoors around late February (Feb 27–Mar 20) in Billings, based on its local frost dates. Confidence 86%.
When can I transplant onion outdoors in Billings?
Transplant outdoors around late April (Apr 28–May 19) in Billings, based on its local frost dates. Confidence 87%.
How long is the growing season in Billings?
Billings has roughly 150 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 Billings's frost dates.
Confidence 90/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.