When to Plant Onion in California

Growing Onion in California: Complete Guide

Onion (Allium cepa) is a warm-season crop that needs a head start indoors before California's last frost. Depending on your zone, California gardeners start seeds indoors between November 6, 2026 (Zone 11a) and February 28, 2027 (Zone 5b), then move transplants outside once their zone's last frost has passed — the zone table above has your exact dates.

Because California stretches across 12 USDA hardiness zones (5b, 6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b, 10a, 10b, 11a), planting windows can shift by as much as six to eight weeks from one end of the state to the other. Gardeners in the warmer southern zones can start earlier, while those in cooler northern zones should wait until the zone table above shows their last frost has passed.

With 100 days to maturity, Onion needs the indoor head start that California's growing season requires. Starting indoors ensures you have strong transplants ready the moment outdoor conditions are right.

Onion requires full sun (6+ hours) and moderate moisture. California's microclimates vary widely — coastal gardens stay cooler while inland valleys can reach extreme summer heat.

For the most precise planting dates tailored to your exact location, enter your ZIP code on our planting calendar or use the zone table above to find the schedule for your area of California.