When to Plant Onion in Ajo, Arizona (85321)

Location

Ajo, Arizona

ZIP Code

85321

USDA Zone

Last Frost

Tuesday, February 10, 2026

📅 Planting Calendar

Start Seeds Indoors Tuesday, December 16, 2025

Transplant Outdoors Tuesday, February 24, 2026

Pro Tip: Start Onion seeds indoors 8 weeks before your last frost date, then transplant outdoors around Tuesday, February 24, 2026.

🌿 Plant Details

Scientific Name Allium cepa

Days to Maturity 100 days

Mature Height 12-18"

Spread 4"

Type Bulb

Fruit Size Medium (2-4 inch bulb)

☀️ Growing Requirements

☀️

Sun

Full Sun (6+ hours)

💧

Water

Moderate

↔️

Spacing

4" apart

🌱

Planting Depth

0.5" deep

Seeds typically germinate in 7-10 days

Ready to Plant Onion in Ajo?

Get your seeds now so they're ready by Tuesday, December 16, 2025.

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🤝 Good Companions

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⚠️ Avoid Planting Near

BeanPeaAsparagus

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Growing Onion in Zone 9b

Onion (Allium cepa) is a popular garden vegetable. In Ajo, Arizona, which is in USDA Hardiness Zone 9b, you should start seeds indoors around Tuesday, December 16, 2025.

Your average last frost date is Tuesday, February 10, 2026. Plan to transplant your Onion seedlings outdoors around Tuesday, February 24, 2026, about 2 weeks after your last frost date.