When to plant summer squash / zucchini in Seattle
Summer squash / Zucchini is frost-tender, so every date keys off Seattle's last spring frost of Mar 17.
Step 1 · Sow
Start seeds indoors
Mar 30 – Apr 20
Before your last frost, on a warm windowsill or heat mat.
Step 2 · Plant
Transplant outdoors
Jun 6 – Jun 27
Once frost risk has passed and nights stay mild.
Step 3 · Harvest
Harvest window
Jul 21 – Aug 5
Picking runs until conditions turn against the crop.
Window
Days to maturity
45 – 60 d
Seattle's 237-day season leaves this much room.
Summer squash / Zucchini on Seattle'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 17
NOV 13
Common questions
When can I sow summer squash / zucchini outdoors in Seattle?
Direct-sow around early June (Jun 6–Jun 27) in Seattle, based on its local frost dates. Confidence 81%.
When will summer squash / zucchini be ready to harvest in Seattle?
Expect to harvest from around late July (Jul 21–Aug 5) in Seattle, based on its local frost dates. Confidence 75%.
When should I start summer squash / zucchini seeds indoors in Seattle?
Start seeds indoors around late March (Mar 30–Apr 20) in Seattle, based on its local frost dates. Confidence 79%.
When can I transplant summer squash / zucchini outdoors in Seattle?
Transplant outdoors around early June (Jun 6–Jun 27) in Seattle, based on its local frost dates. Confidence 81%.
How long is the growing season in Seattle?
Seattle has roughly 237 frost-free days, which is enough time to grow summer squash / zucchini to maturity outdoors.
The rule of thumb
Sow summer squash / zucchini 6–8 weeks before your last spring frost; plant out 2–3 weeks after it. Every date on this page is derived from that rule and Seattle's frost dates.
Confidence 83/100 · Curated · based on NOAA GHCN-Daily 1991–2020 normal · frost dates are probabilities, not guarantees.