Planting Guides

When to Plant Onions in San Diego: Complete Guide + Best Varieties for Zone 10b

San Diego, California

USDA Zone 10b

Last Frost: Feb 1

Last updated: October 30, 2025

Learn when to plant onions in San Diego with specific dates for Zone 10b. Compare 6 varieties, get planting timeline, and discover which onions thrive in Southern California.

EEmma Chen

October 30, 2025

Short-day onions growing in San Diego Zone 10b garden bed with winter vegetables — — Image © PlantReference.org 2026

Quick Answer

Plant short-day onions in San Diego October through December for spring harvest. Choose varieties needing 10-12 daylight hours to bulb properly.

TL;DR

Plant short-day onions in San Diego from October through December for spring harvest. Choose varieties like Allium cepa 'Texas Early Grano' or Allium cepa 'Granex' that bulb with 10-12 hours of daylight. Start transplants November 1-December 15, harvest March-May when bulbs reach full size.

Frequently Asked Questions

When exactly should I plant onions in San Diego?

Plant short-day onion transplants from October through December in San Diego. The optimal window is November 1-30 for most varieties. This timing takes advantage of our mild winters for establishment and spring day-length increases for bulb development. Avoid planting after January as bulbs won't reach full size before summer heat arrives.

Why can't I grow Walla Walla or other popular onion varieties in San Diego?

San Diego sits at 32.7°N latitude, requiring short-day onions that bulb with 10-12 hours of daylight. Popular varieties like 'Walla Walla' and 'Red Wing' need 14-16 hours (long-day types) which our latitude never provides. Plant these varieties and you'll get huge green tops but no bulbs—it's a waste of an entire growing season.

What's the difference between planting onion sets versus transplants in San Diego?

Transplants work best in San Diego because they offer better variety selection for short-day types and establish more reliably in our climate. Sets (small dormant bulbs) have limited short-day varieties available and can bolt if stressed by temperature fluctuations. Transplants cost more but provide much higher success rates for Zone 10b conditions.

Can I plant onions in spring in San Diego?

Spring planting works poorly in San Diego because short-day onions planted in March-April don't have enough cool weather for proper establishment before summer heat arrives. Fall planting (October-December) is essential for giving plants the long, cool growing period they need to develop large bulbs before hot weather triggers dormancy.

How do I prevent my onions from bolting in San Diego?

Prevent bolting by planting appropriate short-day varieties after November 1 when temperatures stabilize, protecting young plants from cold snaps below 35°F (2°C) with row covers, and maintaining consistent watering and fertilization. Avoid planting too early when plants are small and vulnerable to temperature stress that triggers premature flowering.

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Written By

Emma Chen

Emma runs a small succulent propagation business from her home in San Diego, shipping starter plants and cuttings across the country. She fell into succulents after college when she realized they were the only plants that survived her travel schedule—she was working as a travel nurse at the time. San Diego's mild, dry climate is ideal for outdoor succulent gardens, and Emma's front yard is a living catalog of over 200 varieties. She completed a certificate program in ornamental horticulture and writes about succulent care, propagation techniques, and drought-tolerant garden design. Her writing is calm and reassuring—she knows people feel bad about killing plants, and she wants them to stop worrying so much.