Botanical Name: Allium cepa
Days to Maturity: 100–125 days
Native: Exists only in cultivation
Hardiness: Biennial grown as an annual
Variety Information: Yellow, slightly flattened, globe onion, 4"–6" in diameter and weighing around 2 lbs. with dry, papery skin and 6"–10" tops. 'Walla Walla' is a bulbing, yellow, long-day, sweet onion with a short storage period.
Type: Long-day, sweet onion (Learn more)
When to Sow Outside: 4 to 6 weeks before your average last frost date, or as soon as soil can be worked; when soil temperature is at least 45°F.
When to Start Inside: RECOMMENDED. 10 to 12 weeks before your average last frost date. Transplant outdoors 4 to 6 weeks before your average last frost date. The earlier the start, the bigger the bulb. Ideal soil temperature is 60°–85°F.
Days to Emerge: 7–15 days
Seed Depth: ¼"
Seed Spacing: A group of 2 seeds every 6"–8"
Row Spacing: 12"–16"
Thinning: When 2" tall, thin to 1 every 6"–8"
Harvesting: When onion tops have fallen over and turned yellow or brown, they are ready for harvest. Harvest in the morning, lifting onions with a garden fork. Dry them in the garden in the sun for 2 to 3 days, lightly covering the bulbs with straw, or the tops of other onions to prevent sunscald. Cure onions for 3 to 7 days in a dry area with good air circulation. Once dry, cut the roots to 1/4", and the greens to 1" to create a seal, preventing decay.