When should I plant Onion in Zone 9a?

Start Onion seeds indoors around Jan 9. Transplant outdoors after Feb 20. Expect first harvest around May 11.

What is the last frost date for Zone 9a?

The average last spring frost date for Zone 9a is Mar 20. The first fall frost averages Nov 12, giving a 237-day growing season.

Can I grow Onion in Zone 9a?

Yes. Onion needs 110 days to harvest. Zone 9a has a 237-day growing season, which is sufficient.

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🧅 Growing Onion in Zone 9a

Zone 9a has warm winters and an extended growing season — excellent for heat-loving crops like Onion. Last frost: Mar 20. First frost: Nov 12.

Planting Calendar

Indoor

Outdoor

Harvest

Jan 9Nov 12

Season: Mar 20 – Nov 12 (237 days)

Zone9a

Last FrostMar 20

First FrostNov 12

Season Length237 days

Days to Harvest110

SunFull Sun

Frost ToleranceModerate

Spacing9/sqft (4" apart)

When to Plant Onion in Zone 9a

Start Seeds Indoors: Jan 9

Start Onion seeds indoors around Jan 9 (10 weeks before last frost). Optimal germination temperature: 70°F. Germinates in 7–14 days.

Transplant Outdoors: Feb 20

Transplant Onion seedlings outdoors after Feb 20. 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 11

First harvest approximately May 11 (~80 days from transplant). Continue harvesting until first frost (Nov 12).

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

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