Days to Maturity: 110–120 Days
Native: Exists only in cultivation
Hardiness: Frost-tolerant biennial grown as annual
Variety Information: Flattened bulbs, 1½"–3" wide, and ¾"–1½" high. 'Borettana' is bronze-skinned, white-fleshed. Stores up to 5 months.
Type: Long day, storage cipollini (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 4"
Row Spacing: 8"–12"
Thinning: When 2" tall, thin to 1 every 3"
Special Care: Keep growing area weed-free. Onion size can decrease 4% per day if competing with weeds—that's 50% in two weeks. If bulb pushes itself out of the ground, you may cover it lightly with straw, but not soil, as soil will prevent the onion bulb from forming properly.
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 ¼", and the greens to 1" to create a seal, preventing decay.