PREPARATION: Onions require full sun and fertile, well-drained soil with a pH of 6.0-7.0. Sandy loam soils with good moisture retention are recommended. Add some peat moss can help with moisture retention.
DIRECT SEEDING: Sow bunching onions at 24 seeds/foot and bulb onions at 12 seeds/foot, 1/4″ deep, rows 12-18″ apart. Thin bunching onions to every 1″ and bulb onions to every 4″.
TRANSPLANTING: In short-season areas, sow seeds indoors in flats in late February to mid-March. 2-3 seeds per cell and thin when 2″ tall. Tops may be clipped to 5″ tall. Transplant to the garden 1″ apart for bunching and 4″ apart for larger bulbs.
WATER: Onions are shallow rooted and grow best with at least 1″ per week of rain or irrigation, especially during the bulbing phase.
HARVEST: When necks become soft and tops are falling over, pull and sun-cure at least 2-7 days, depending on weather. Move to a protected location to finish drying.
STORAGE: When dry, clip off tops and roots and store in onion bags or shallow boxes at near freezing and 65-70% humidity.
DAY LENGTH: Onion bulbing is triggered by day length, and maximum day length during the growing season increases from south to north. Short-day onions are grown at lower latitudes in the South, while intermediate and long-day onions are grown at higher latitudes. Refer to “Adaptation” in each variety description for details.