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🧅 Growing Onion in Zone 9b

Zone 9b has warm winters and an extended growing season — excellent for heat-loving crops like Onion. Last frost: Mar 10. First frost: Nov 15.

Planting Calendar

Indoor

Outdoor

Harvest

Dec 30Nov 15

Season: Mar 10 – Nov 15 (250 days)

Zone9b

Last FrostMar 10

First FrostNov 15

Season Length250 days

Days to Harvest110

SunFull Sun

Frost ToleranceModerate

Spacing9/sqft (4" apart)

When to Plant Onion in Zone 9b

Start Seeds Indoors: Dec 30

Start Onion seeds indoors around Dec 30 (10 weeks before last frost). Optimal germination temperature: 70°F. Germinates in 7–14 days.

Transplant Outdoors: Feb 10

Transplant Onion seedlings outdoors after Feb 10. Wait until soil temperature reaches 45°F. Space plants at 9/sqft (4" apart). Harden off plants for a week before moving outside.

Harvest: May 1

First harvest approximately May 1 (~80 days from transplant). Continue harvesting until first frost (Nov 15).

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 9b?

Start Onion seeds indoors around Dec 30. Transplant outdoors after Feb 10. Expect first harvest around May 1.

What is the last frost date for Zone 9b?

The average last spring frost date for Zone 9b is Mar 10. The first fall frost averages Nov 15, giving a 250-day growing season.

Can I grow Onion in Zone 9b?

Yes. Onion needs 110 days to harvest. Zone 9b has a 250-day growing season, which is sufficient.

What is the best month to plant Onion in Zone 9b?

The best time to start Onion in Zone 9b is Dec. Begin seeds indoors around Dec 30, then transplant outdoors after the last frost date of Mar 10.

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 9b, expect your first harvest around May 1.

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