Onion Seeds,
Round Tropea

Start seeds indoors three months before the last expected frost date in spring. Transplant acclimated, stocky seedlings into the garden 4-6 weeks before the last frost of spring, as onions can tolerate light frosts. An intermediate- to long-day onion, it bulbs where summer day length reaches about 12-14 hours or more, suiting mid-latitude and northern gardens. If you're not sure how to find your area's day length or first and last frost dates, consult our blog post 'Our Experts Answer Questions, Share Resources.'

Plant seeds 1/4 inch deep in seed-starting trays or sow directly into the soil after frost has passed. Maintain soil temperatures around 60 F for germination, which typically takes 7-14 days. Space plants 4-6 inches apart with 12 inches between rows to give room for the round bulbs to form.

Fertilize regularly with a balanced fertilizer or compost tea every 2-3 weeks. Keep the soil consistently moist, but don’t overwater to prevent root rot. Keep the area weed-free and use mulch to improve water retention. As the bulbs mature and the tops yellow, reduce watering to prepare for harvest.

• Onions will cross with other onions, and occasionally they will cross with scallion types like Welsh onions and Hi Shi Ko bunching onions. Onions will never cross with leeks, chives or garlic.
• If you are growing types that will cross, try to isolate varieties by at least several hundred feet or ideally up to one mile.
• Onions are a biennial seed crop, so you will need to overwinter your first-year roots, ideally by digging them up and storing them for the winter. Replant in early spring, and allow onions to shoot up spikes of purple flowers.
• Let seeds become dry on the plants. Pick seeds when they are hard and dark black, then bring them indoors to finish drying.
• Once dry, separate the seeds from the husks or leave them on and plant them husks and all.