When to plant onions in zone 9a

The zone 9a schedule for onions

Start seeds indoors

November 10 to December 22

Plant out

February 2 to 16

Sow outdoors

January 19 to February 2

From the median frost dates of the NOAA stations assigned to the 1,736 ZIP codes in zone 9a, and the timing recommended by Cooperative Extension guides for onions.

Dates before the last frost assume the soil has thawed and is dry enough to work: a squeezed handful crumbles instead of sticking. After a late or wet spring, wait for that even if the date has passed.

Frost risk in zone 9a

Zones are based on winter cold, not on frost dates, so the last spring frost varies a lot within a zone. Across zone 9a, the typical last frost ranges from about February 13 in the earliest tenth of ZIP codes to March 21 in the latest tenth, and the first fall frost from November 14 to December 9. For a typical place in the zone:

• February 4Risky: a later frost happens in 9 years out of 10
• March 2Typical: frost after this date in half of years
• March 25Safe: a later frost only 1 year in 10

Onions in zone 9a cities