How to Grow Walla Walla Onion
Wikimedia Commons
Walla Walla Onion
Allium cepa var. cepa
vegetableWalla Walla onions are a large, sweet yellow onion variety named after the Walla Walla Valley in Washington state. Known for their exceptional sweetness, mild flavor, and thin papery skin, they are among the most prized cooking and fresh-eating onions. These bulbs can reach 4-5 inches in diameter and are best grown in regions with long growing seasons.
When should you plant Walla Walla Onion in your zone?
Get a personalized planting timeline — when to start seeds, transplant, and harvest — based on your USDA zone and local frost dates. Free to start.
Example Walla Walla Onion timeline · Pittsburgh, PA (Zone 6b)
-
Plant Walla Walla Onion
Around Apr 17Near Pittsburgh's average last spring frost.
-
Tend & protect
Late spring–summerWatering, feeding, and pest-watch reminders.
-
Harvest Walla Walla Onion
Around Aug 15≈ 120 days after planting
Sample dates for Pittsburgh, PA. Sign up to get exact Walla Walla Onion dates for your own zip code.
Growing Conditions
Soil
Growing Zones
Find your zone →Zones 3-9; most successful in zones 5-8 with long, cool growing seasons
Sign up free to see if Walla Walla Onion grows in your zone — and get a personalized planting timeline.
Get my Walla Walla Onion timeline →Growth Stages
Dormancy & Chilling
Varies; occurs in winter/early springWalla Walla onions require vernalization (cool temperatures) to trigger bulbing. Sets should be stored at cool temperatures before spring planting.
Purchase cold-stored sets or plant seeds in fall in mild climates; ensure 8+ weeks of temperatures below 55°F for proper development
Sprouting & Establishment
2-4 weeksShoots emerge from sets within 1-2 weeks; seedlings develop 2-3 true leaves and establish root systems.
Keep soil consistently moist but not waterlogged; thin seedlings to proper spacing; provide steady temperatures of 50-70°F
Vegetative Growth
6-10 weeksFoliage develops rapidly; plants produce 5-8 long green leaves and begin forming shallow roots. Bulbing has not yet initiated.
Water deeply 1-2 times weekly; apply 1-2 inches of mulch around plants; fertilize every 3 weeks with balanced fertilizer; keep area weed-free
Bulbing & Maturation
6-8 weeksAs day length increases (or naturally in late spring/early summer), bulbs begin swelling. Underground development accelerates while foliage growth slows.
Reduce watering as bulbs mature; shift to low-nitrogen fertilizer; stop overhead watering to prevent disease; monitor for splitting due to erratic moisture
Harvest & Curing
7-14 days curing; harvest in late summerTops yellow, fall over, and dry. Papery outer skin develops. Bulbs are firm with thin necks.
Harvest when 50-75% of tops have fallen over; pull and lay on soil in single layer for 1-2 weeks to cure and skin harden; store in cool, dry location
Common Pests
-
Use row covers early in season; apply diatomaceous earth; rotate crops; destroy infested bulbs; use reflective mulches
-
Spray with insecticidal soap or neem oil; increase air circulation; remove weeds; encourage natural predators
-
Row covers; crop rotation; remove plant debris; set traps for monitoring
-
Use disease-free sets; improve drainage; avoid injuring bulbs during harvest; store at 32-40°F with low humidity
-
Improve air circulation; avoid overhead watering; apply sulfur fungicide; ensure adequate spacing
Uses
Fresh eating and salads
CulinaryWalla Walla onions are exceptionally sweet and mild, making them ideal for eating raw in salads, on sandwiches, or caramelized. Their natural sugars (higher than most onion varieties) become even more pronounced when grilled or sautéed. [source]
Cooking and flavor base
CulinaryThe sweet, complex flavor of Walla Walla onions enriches soups, stews, curries, and French onion soup. Unlike pungent onion varieties, their sweetness mellows further with slow cooking. [source]
Long-term storage
HouseholdWhen properly cured and stored in cool, dry conditions, Walla Walla onions can be preserved for 2-4 months, extending their use well into winter. [source]
Quercetin and antioxidants
MedicinalLike all onions, Walla Walla onions contain quercetin, a flavonoid with potential anti-inflammatory and antioxidant properties. They also provide vitamins C, B6, and manganese. [source]
Natural dye production
HouseholdThe papery yellow-brown outer skins of Walla Walla onions have been traditionally used to create natural dyes for textiles, producing warm golden and brown hues. [source]
This is not medical advice. LizPlants is not a medical resource. Always consult a qualified healthcare professional before using plants medicinally.
Harvest Tips
Harvest in late summer when 50-75% of tops have yellowed and fallen over, typically late July through August in most regions. Gently pull entire plant and lay bulbs in a single layer on dry soil or in a shaded area to cure for 7-14 days. Once outer skin is papery and necks are completely dry, trim roots to 0.5 inches and store in a cool (32-40°F), dry, well-ventilated location. Properly cured Walla Walla onions can store for 2-4 months.
Fun Facts
- 🌱 Walla Walla onions are named after the Walla Walla Valley in southeastern Washington state and northeastern Oregon, where they were cultivated as early as the 1880s. The valley's volcanic soil, cool nights, and long daylight hours create ideal growing conditions for their exceptional sweetness.
- 🌱 The sweetness of Walla Walla onions is due to their naturally high sugar content and relatively low levels of sulfur compounds compared to other onion varieties. This makes them less likely to cause tears when cut, earning them the nickname 'sweet onion.'
- 🌱 Walla Walla onions are designated as the official state vegetable of Washington. They hold a special place in Pacific Northwest agriculture and regional cuisine, with annual festivals celebrating the harvest.
Gardening Terms
New to gardening? Learn about terms used in this guide:
Join 30,000 gardeners planning their gardens with LizPlants.
Get your personalized Walla Walla Onion planting timeline
Tell us your zip code and we'll calculate exactly when to start Walla Walla Onion seeds, transplant seedlings, and harvest — based on your USDA zone and local frost dates. Includes calendar reminders and printable task lists. Free to start.
Get my Walla Walla Onion timeline →