Arizona · zones 5b–10a
When to plant onions in Arizona.
Sow or transplant between Jan 1 to Jan 11 in a typical year, keyed to Arizona's median last frost around Feb 5. Dates below are state medians; your ZIP code shifts them by days to weeks.
The 2026 windows
Onions dates for a typical Arizona season.
1 · Start indoors
Nov 20 to Nov 30
About 6 weeks before set-out. Warm spot, real light.
2 · Set out
Jan 1 to Jan 11
Keyed to the ~Feb 5 last frost. Sow 0.5" deep, 4" apart.
Harvest
~95 days later
~0.5 lb per plant over ~1 weeks.
Arizona spans more than one climate: Zone 9 is the most common zone, but the state runs 5b to 10a. 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.