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🧅 Growing Onion in Zone 10b

Zone 10b has a year-round growing season. Onion can be planted almost any time with proper planning. Last frost: Jan 28. First frost: Dec 22.

Planting Calendar

Indoor

Outdoor

Harvest

Nov 19Dec 22

Season: Jan 28 – Dec 22 (328 days)

Zone10b

Last FrostJan 28

First FrostDec 22

Season Length328 days

Days to Harvest110

SunFull Sun

Frost ToleranceModerate

Spacing9/sqft (4" apart)

When to Plant Onion in Zone 10b

Start Seeds Indoors: Nov 19

Start Onion seeds indoors around Nov 19 (10 weeks before last frost). Optimal germination temperature: 70°F. Germinates in 7–14 days.

Transplant Outdoors: Dec 31

Transplant Onion seedlings outdoors after Dec 31. Wait until soil temperature reaches 45°F. Space plants at 9/sqft (4" apart). Harden off plants for a week before moving outside.

Harvest: Mar 21

First harvest approximately Mar 21 (~80 days from transplant). Continue harvesting until first frost (Dec 22).

Companion Planting

✅ Strawberries✅ Cabbage✅ Beets✅ Lettuce✅ Carrots✅ Tomatoes

❌ Beans❌ Peas

Onion in Other Zones

1a 1b 2a 2b 3a 3b 4a 4b 5a 5b 6a 6b 7a 7b 8a 8b 9a 9b 10a 10b 11a 11b 12a 12b 13a 13b

Frequently Asked Questions

When should I plant Onion in Zone 10b?

Start Onion seeds indoors around Nov 19. Transplant outdoors after Dec 31. Expect first harvest around Mar 21.

What is the last frost date for Zone 10b?

The average last spring frost date for Zone 10b is Jan 28. The first fall frost averages Dec 22, giving a 328-day growing season.

Can I grow Onion in Zone 10b?

Yes. Onion needs 110 days to harvest. Zone 10b has a 328-day growing season, which is sufficient.

What is the best month to plant Onion in Zone 10b?

The best time to start Onion in Zone 10b is Nov. Begin seeds indoors around Nov 19, then transplant outdoors after the last frost date of Jan 28.

What companion plants grow well with Onion?

Good companion plants for Onion include Strawberries, Cabbage, Beets, Lettuce, Carrots, Tomatoes. Avoid planting Onion near Beans, Peas.

How long does Onion take to harvest?

Onion takes approximately 110 days from planting to harvest. In Zone 10b, expect your first harvest around Mar 21.

Plan Your Onion Garden

Track Onion from seed to harvest with personalized frost dates, watering recommendations, and companion planting visualization.

Start Free Onion Growing Guide