Choose onion type: short-day (mild winters), intermediate-day, or long-day (cold winters)
Start seeds indoors 6–10 weeks before the last frost, or buy transplants
Sow seeds 1/4 inch deep in seed-starting mix
Keep soil evenly moist and warm (about 60–75°F / 16–24°C) until germination
Provide 12–16 hours of light daily (grow lights if needed)
Harden off seedlings 7–14 days before transplanting
Transplant when seedlings have sturdy growth (typically pencil-thickness) and after frost risk passes
Space plants 2–4 inches apart in rows 12–18 inches apart (adjust by variety and desired bulb size)
Plant in full sun (at least 6–8 hours/day)
Use well-draining soil with plenty of organic matter
Fertilize at transplant with a balanced fertilizer, then feed again when bulbs begin forming
Water consistently to keep soil evenly moist (avoid drought stress)
Water deeply about 1 inch per week total (more during hot, dry weather)
Mulch lightly to help maintain moisture and reduce weeds
Weed regularly, especially early, to prevent competition
Thin seedlings if starting in place so bulbs have room
Avoid nitrogen-heavy feeding late in the season to reduce soft growth
Watch for common issues: onion thrips, downy mildew, and purple blotch
Control pests with good airflow, proper spacing, and appropriate labeled treatments if needed
Stop watering when tops begin to yellow and fall over (final bulbing stage)
Harvest when 50–80% of tops have fallen over and bulbs are firm
Lift gently to avoid bruising bulbs
Cure onions in a dry, well-ventilated area out of direct sun for 2–4 weeks
Cut tops after curing, leaving about 1 inch of neck
Store cured onions in a cool, dry, well-ventilated place (ideal around 0–4°C / 32–40°F for many varieties)