Washington · zones 6b–9a
When to plant onions in Washington.
Sow or transplant between Feb 4 to Mar 20 in a typical year, keyed to Washington's median last frost around Apr 14. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Onions dates for a typical Washington season.
1 · Start indoors
Dec 24 to Feb 6
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Feb 4 to Mar 20
Keyed to the ~Apr 14 last frost. Sow 0.5" deep, 4" apart.
Harvest
~95 days later
~0.5 lb per plant over ~1 weeks.
Washington spans more than one climate: Zone 8 is the most common zone, but the state runs 6b to 9a. That's why the planner works from your ZIP code's frost dates, not your zone — mountain and coastal gardens in the same state can be three weeks apart.