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.

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.

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 long- and intermediate-day areas, sow indoors 6–8 weeks before last frost date. Sow 128-cell trays, 1 seed/cell, and cover with 1/4" soil. Transplant 4" apart in rows 12–18" apart. Unruly tops may be clipped to 5" at time of transplant.

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 50% of tops are falling over, pull and cure in well-ventilated space out of direct sunlight (to prevent greening) or sun-cure in field for 2–7 dry days before moving to dry location. Cure until tops are completely dried; about 2 weeks.

STORAGE:

When dry, clip off tops and roots and store in onion bags or shallow boxes at near freezing and 65–70% humidity.

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 at 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.

Onions