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Allium cepa 'Walla Walla'
Walla Walla Sweet Onion
Cultivar developed in the early 1900s in the Walla Walla Valley, Washington State, by Italian immigrants; the species A. cepa is native to Central Asia (Iran, Afghanistan, Pakistan)
Overview
Allium cepa 'Walla Walla' is the Walla Walla sweet onion, a biennial grown as an annual for bulb production, 18-24 inches (45-60 cm) tall and 4-6 inches (10-15 cm) wide. Flattened globe-shaped bulbs 3.5-4.5 inches (9-11 cm) diameter with golden-tan papery outer skins and thick succulent white flesh. A sweet onion: reduced sulfur compounds and elevated sugar content (5-6% vs. 3-4% in storage types) — mild enough to eat raw. Blue-green hollow tubular foliage. In the amaryllis family (Amaryllidaceae). A long-day onion: requires 14-16 hours of daylight to trigger bulbing (suited to latitudes above 36°N). Developed by Italian immigrants in the Walla Walla Valley, Washington, in the early 1900s. The thick neck (0.75-1 inch / 2-2.5 cm) limits storage life to 2-3 months — significantly shorter than thin-necked storage types (6-8 months). Start seed indoors 10-12 weeks before last frost; transplant 4-6 weeks before last frost. Harvest when 50-75% of the tops have naturally fallen over and yellowed (110-125 days from transplant). All Allium species contain thiosulfates: toxic to dogs, cats, and horses (causes Heinz body anemia). Onion maggot (Delia antiqua) and thrips are the primary pests. Deer-resistant (aromatic). Full sun. Annual. Growth rate is moderate.
Native Range
Cultivar developed in the early 1900s in the Walla Walla Valley, Washington State, by Italian immigrants. The species A. cepa is native to Central Asia (Iran, Afghanistan, Pakistan).Suggested Uses
Grown in vegetable gardens and containers of at least 3 gallons (11 L). Sweet onion — mild enough for raw eating. Long-day type (latitudes above 36 degrees N). Stores only 2-3 months. Toxic to pets. Deer-resistant. Annual.How to Identify
Appearance
Size & Dimensions
Height1'6" - 2'
Width/Spread4" - 6"
Reaches mature size in approximately 1 years
Bloom Information
Biennial: flowers in the second year if overwintered — white to greenish-white spherical umbels on a hollow scape. Grown as an annual for bulb production. Bolting in the first year reduces bulb size — cut flower scapes immediately.Detailed Descriptions
Flower Description
White to greenish-white spherical umbels 2-3 inches (5-7 cm) on a hollow scape 24-36 inches (60-90 cm) — only if allowed to bolt in the second year; flowering is undesirable in bulb productionFoliage Description
Blue-green, hollow tubular, 0.5-0.75 inch (12-18 mm) diameter; yellows naturally at maturityGrowing Conditions
Sun Requirements
Requires 6-12 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Full sun (6+ hours). Well-drained fertile soil pH 6.0-7.0. Long-day onion — requires 14-16 hours daylight for bulbing (latitudes above 36 degrees N). Start seed 10-12 weeks indoors. Consistent moisture during bulb swelling. Reduce watering as tops yellow. All Allium toxic to dogs, cats, horses. Onion maggot and thrips. Deer-resistant. Stores 2-3 months only. Annual.Pruning
Cut any flower scapes at the base immediately if they appear. Do not cut green foliage during growth — the leaves feed the bulb. Harvest when 50-75% of tops have fallen and yellowed. Trim tops to 1-2 inches (2.5-5 cm) above the neck after harvest. Cure for 2-3 weeks in a warm dry location before storage.Maintenance Level
moderateContainer Growing
✓ Suitable for container growing
Minimum container size: 3 gallons
⚠️ Toxicity Warning
Toxic to petsPlanting Guide
Planting Methods & Timing
Planting Method
transplant
Indoor Start
10 weeks before last frost
Direct Sow Timing
Late summer to early fall for overwintering in mild climates (zones 7-9)
Days to Maturity
110–125 days
Plant Spacing
4 inches