Planting Guides

When to Plant Onions in San Francisco: Complete Guide + Best Varieties for Zone 10a

San Francisco, California

USDA Zone 10a

Last Frost: Jan 15

Last updated: October 30, 2025

Learn when to plant onions in San Francisco with specific dates for Zone 10a. Compare 6 varieties, get a complete timeline, and discover which onions grow best in California's mild climate.

DDavid Kim

October 30, 2025

When to plant onions in San Francisco Zone 10a garden with Victorian houses background — — Image © PlantReference.org 2026

TL;DR

Plant onions in San Francisco September through November for best results in Zone 10a. Use intermediate-day or short-day varieties like Allium cepa 'Candy' and Allium cepa 'Red Creole'. San Francisco's unique coastal climate allows nearly year-round growing, but fall planting avoids summer fog stress and produces larger bulbs by late spring harvest.

Frequently Asked Questions

When should I plant garlic in San Francisco?

Plant garlic cloves in San Francisco during October through December for Zone 10a conditions. Softneck varieties like Allium sativum 'California Early' perform best in the Bay Area's mild winters. Plant cloves 2-3 inches deep and 6 inches apart in well-draining soil. Harvest occurs 8-9 months later in June through August when bottom leaves begin yellowing.

Can I grow onions year-round in San Francisco?

Yes, San Francisco's Zone 10a climate allows nearly year-round onion production with proper variety selection and succession planting. Plant intermediate-day varieties every 6-8 weeks from September through March for continuous harvest. Avoid summer planting (June-August) when fog stress reduces bulb quality. Bunching onions Allium fistulosum can be grown continuously with harvests every 60-70 days.

Why don't my onions form bulbs in San Francisco?

Poor bulb formation in San Francisco typically results from using long-day varieties that require warmer temperatures than the city's cool summers provide. Choose intermediate-day varieties like Allium cepa 'Candy' or short-day varieties like Allium cepa 'Red Creole' that bulb reliably in cool coastal conditions. Long-day varieties need sustained temperatures above 75°F which rarely occur in San Francisco.

How do I protect onions from San Francisco's summer fog?

Protect onions from fog stress by choosing fog-tolerant varieties, using clear row covers during persistent fog periods, and planting in raised beds for better soil warming. Position beds in protected microclimates on the south or west side of structures where they receive maximum available sunlight. Increase potassium fertilization to improve plant stress tolerance during the fog season.

What's the best soil amendment for San Francisco's clay soil?

Improve San Francisco's heavy clay soil by adding coarse sand (not fine sand) at a 1:1 ratio with existing soil, plus 2-3 inches of compost annually. Create raised beds minimum 8 inches high for drainage during winter rains. Never add fine sand to clay as this creates concrete-like conditions. Consider adding perlite or pumice for long-term drainage improvement in clay soils.

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Tagged with

#when to plant onions san francisco #zone 10a onions #san francisco gardening #california onion varieties #intermediate day onions #coastal gardening #bay area vegetables #fog tolerant onions #fall planting onions #san francisco soil

Written By

David Kim

David is a software engineer who got into gardening after buying a fixer-upper in the Sunset District with a neglected backyard. San Francisco's microclimates fascinated him—he quickly learned that what grows three blocks away might not work in his fog belt yard. David now maintains a productive vegetable garden despite the marine layer, growing cool-season crops almost year-round and experimenting with season extension techniques. He volunteers at a local community garden and writes about urban food growing, microclimate gardening, and the particular challenges of Bay Area conditions. His approach is methodical—he keeps detailed notes and isn't afraid to share what didn't work.