Plant Onions in Zone 9a

Seed-starting, transplant & harvest dates for USDA Zone 9a

Start indoors

Dec 21

Transplant

Feb 15

Harvest (~100d)

May 26

Zone 9a averages 274 frost-free days, running from a last spring frost around March 1 to a first fall frost around November 30. Onions needs roughly 100 days from planting out to first harvest, so it uses about 36 percent of that window. Onions is a hardy crop, which is what decides where in the window it belongs.

Because onions needs a head start, sow seed indoors around Dec 21, about 10 weeks ahead of the Zone 9a last frost. Transplants go out around Feb 15. Starting earlier than that in Zone 9a usually backfires: plants outgrow their cells and stall when they finally hit cold soil. At 100 days to harvest, a 274-day Zone 9a season has room for about 2 sowings, so stagger them rather than planting everything at once.

Planting onions for a fall harvest in Zone 9a

Yes. Plant onions between October 19 and November 9 in Zone 9a, roughly 6 to 3 weeks before the average first frost, so it roots before the ground freezes.

Short-day onion sets planted in fall overwinter in zone 7 and warmer and bulb up months ahead of a spring planting.

Plant from

Oct 19

Plant by

Nov 9

Overwinters, harvest in spring

Spring

Fall dates are counted backward from the Zone 9a average first frost, not forward from a sowing date. See the fall planting calendar by zone for the full method.

Spring vs fall onions in Zone 9a

Planting	Sow or start	In the ground	Harvest
Spring	Dec 21	Feb 15	May 26
Fall	by Nov 9	Nov 9	Next spring

Last spring frost

Mar 1

First fall frost

Nov 30

Growing season

274 days

Onions in nearby zones

Onions in Zone 8b (colder) Onions in Zone 9b (warmer) Full Onions grow guide Zone 9a planting calendar

Other crops in Zone 9a

Tomatoes in Zone 9a Peppers in Zone 9a Cucumbers in Zone 9a Lettuce in Zone 9a Zucchini in Zone 9a Carrots in Zone 9a Beans (bush) in Zone 9a Peas in Zone 9a Broccoli in Zone 9a Spinach in Zone 9a Kale in Zone 9a Garlic in Zone 9a Potatoes in Zone 9a Squash (winter) in Zone 9a Corn in Zone 9a Radishes in Zone 9a Beets in Zone 9a Eggplant in Zone 9a Basil in Zone 9a Cilantro in Zone 9a Parsley in Zone 9a Pumpkins in Zone 9a Sunflowers in Zone 9a

Frequently asked questions

When should I start onions in Zone 9a?

Start onions seeds indoors around Dec 21 (Zone 9a).

Can I direct sow onions in Zone 9a?

Onions is best started indoors and transplanted in Zone 9a rather than direct sown.

Can I plant onions in the fall in Zone 9a?

Yes. Plant onions between October 19 and November 9 in Zone 9a, roughly 6 to 3 weeks before the average first frost, so it roots before the ground freezes.

Will onions survive frost in Zone 9a?

Onions is a hardy crop and keeps going roughly 21 days past the first light frost in Zone 9a. A row cover or a straw mulch buys more.

How many plantings of onions fit in a Zone 9a season?

About 2. Zone 9a averages 274 frost-free days and onions needs roughly 100 days plus a couple of weeks of turnaround, so sowing every 57 days keeps a supply coming.