Planting Guides
When to Plant Onions in Portland: Complete Guide + Best Varieties for Zone 8b
Portland, Oregon
USDA Zone 8b
Last Frost: Mar 20
Last updated: January 15, 2026
Learn when to plant onions in Portland with specific dates for Zone 8b. Compare 6 varieties, get a complete timeline, and discover which onions grow best in Oregon.
— Image © PlantReference.org 2026
TL;DR
Plant onions in Portland March 1-15 for spring harvest or October 15-30 for early summer harvest. Choose long-day varieties like Allium cepa 'Walla Walla' and Allium cepa 'Red Wing' which thrive in Oregon's latitude. Portland's Zone 8b climate allows both spring and fall planting strategies, with fall-planted onions producing larger bulbs by June.
Frequently Asked Questions
Can I grow onions year-round in Portland?
Portland's Zone 8b climate allows two planting seasons but not continuous growing. Plant in March for fall harvest or October for early summer harvest. Winter temperatures still drop too low for active growth, though fall-planted onions survive with protection.
Why do my onions have small bulbs despite good leaf growth?
This usually indicates wrong variety selection for Portland's latitude. You likely planted intermediate-day or short-day varieties that need shorter day lengths to trigger bulbing. Portland requires long-day varieties that respond to our 15+ hour summer days. Switch to varieties like Allium cepa 'Walla Walla' or Allium cepa 'Red Wing'.
When should I stop watering onions before harvest?
Stop watering Portland onions 2 weeks before harvest when tops begin yellowing naturally. This usually occurs in late August for spring-planted onions. Reducing moisture helps onions cure properly and improves storage life. Our September rains often complicate this timing, so watch weather forecasts.
Can I save seeds from my Portland-grown onions?
Onions are biennial, requiring two years to produce seeds. Leave some bulbs in the ground over winter, and they'll flower the following summer. However, hybrid varieties won't breed true to type. Save seeds only from open-pollinated varieties like Allium cepa 'Yellow Sweet Spanish' for consistent results.
What's the difference between hardneck and softneck garlic for Portland?
Both types grow well in Portland's Zone 8b climate. Hardneck varieties like Allium sativum 'Music' produce edible flower stalks (scapes) and have complex flavors but shorter storage life (6-8 months). Softneck varieties like Allium sativum 'California Early' store longer (10-12 months) and braid well but have milder flavor. Choose based on your storage needs and culinary preferences.
How deep should I plant garlic cloves in Portland?
Plant garlic cloves 2 inches (5 cm) deep in Portland's Zone 8b climate. This provides adequate winter protection while allowing spring emergence. In areas with heavy clay soil, plant slightly shallower (1.5 inches) to prevent waterlogging. Always plant pointed end up with 6 inches (15 cm) spacing between cloves.
Why did my fall-planted onions bolt in spring?
Fall-planted onions bolt when they experience cold followed by warm weather, triggering the plant's natural flowering cycle. Prevent bolting by planting smaller transplants in late October rather than early October, avoiding large sets entirely for fall planting, and providing consistent moisture through winter and spring to reduce stress.
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Dr. Sarah Green
Sarah earned her doctorate in plant biology and spent time working in botanical garden education before transitioning to freelance writing and consulting. Now based in Portland, Oregon, she teaches plant identification workshops at local community centers and maintains a modest collection of over 60 houseplants in her small apartment. Sarah specializes in helping beginners understand plant science without the jargon—her approach focuses on practical observation over theory. She's killed her fair share of fiddle leaf figs and finally cracked the code on keeping them alive.
