Onions - Key Growing Information

A row of developing onion plants in our onion trials at our research farm in Albion, Maine.


SCIENTIFIC NAME: Allium cepa
CULTURE: Onions require full sun and fertile, well-drained soil with a pH of 6.0–7.0. Sandy loam soils are ideal; in heavier soils, use raised beds or raised rows to promote soil drainage.
DIRECT SEEDING: In April or early May, or as soon as the soil can be prepared in early spring, sow in a 2" wide band, about 2 seeds/in., 1/4– 1/2" deep, rows 12–18" apart. Thin to 1 1/2–2" apart for highest yields in fertile soil. Thin to 3-4" apart for larger onions.
TRANSPLANTING: In short-season areas, sow seeds indoors in flats in late February to mid-March. Broadcast 1/2" apart and cover 1/4". Tops may be clipped to 5" tall. Transplant to the garden 4" apart, or sow 5 seeds in each cell of 1–1 1/2" diameter plug trays, thinning to 3 per cell. Transplant each cell 6" apart.
CULTIVATION: Keep onions well weeded with shallow cultivation.
WATER: Onions are shallow rooted and grow best with at least 1" per week of rain or irrigation, especially during the bulbing phase.
DISEASES: Adequate air circulation and crop rotation aids in reducing the risk of foliar disease.
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.
DAYS TO MATURITY: From direct seeding; subtract 10–15 days for days to maturity from transplant.
AVG. DIRECT SEEDING RATE: 1 oz./25', 1M/50', 5M/250', 25M/1,250', 580M/acre @ 20 seeds/ft., in rows 18" apart.
TRANSPLANTS: Avg. 1 oz./4,900 plants, 1 lb./78,750.
SIZED SEEDS: Standard on all varieties.
SEED SPECS: SEEDS/LB.: 96,900–127,700 (avg. 112,000).
PACKET: 250 seeds, sows 12' or makes 140 plants.