What Type of Onion Grows Well in Virginia?

Virginia Climate Zones

• Virginia USDA plant hardiness zones range from zone 5a along the edge of the Appalachians to zone 7b by the shore. USDA zone 7b is a triangular area including Norfolk and Virginia Beach. Virginia's largest climate zone, 7a, forms a broad band running from northeast to southwest through the center of the state. Foothill and mountain areas to the west contain pockets of USDA zone 5b and 6. According to "Organics for All," the 36th latitude, which runs from close to Virginia Beach across the country to San Francisco, is a general dividing line used by plant growers to separate northern from southern climates. With USDA zone 7 extending through the state as far north as the Virginia suburbs of Washington, D.C., climates in various areas of Virginia may seem more northern or southern, depending on local factors, such as tree shade, buildings and paving or wind exposure. Planting more than one type of onion may be the best way to determine exactly which varieties do best in your locale.

Photosensitivity in Onions

• The reason location and climate zone play such important parts in choosing what variety of onions to grow is their sensitivity to day length. The changing seasonal ratio between hours of dark and daylight governs when onions shift from producing top growth to forming bulbs. Top formation correlates directly with bulb size. Day length depends on the relationship between the sun's light and the curvature of the earth. At summer solstice, the longest day of the year, Washington, D.C. receives almost 15 hours of sunlight, while Minneapolis, Minnesota, receives over 15 1/2 hours, and the day in Fairbanks, Alaska, is 22 hours long. Summers in USDA zones 7 and warmer may be hotter, but daylight hours may be shorter. While onions respond to both light and warmth, light is the ultimate governing factor in setting bulbs.

Long-Day Onions

• Long-day onions require 14 to 16 hours of daylight to shift from top growth to bulb production. This makes long-day onions most suitable to northern areas, where spring planting permits ample top formation before long summer days begin. "Walla Walla Sweet" (Allium cepa "Walla Walla Sweet") and "Ebeneezer" (Allium cepa "Ebeneezer") are well-known long-day varieties. "Ebeneezer" is often planted from sets, which are small bulbs grown the previous year, a strategy which can be particularly effective in areas where spring is short.

Short-Day Onions

• Short-day varieties need only 10 to 12 hours of daylight to shift from top production to bulb production. In USDA zones 7 through 10, they are often started from seed in the fall or planted as sets in winter for late spring or summer harvest. In central Virginia, onion seedlings or transplants are most often planted in early spring, with some of the crop harvested as scallions. "Granax" (Allium cepa "Granax") or "Texas Supersweet" (Allium cepa "Texas Supersweet") are widely available short-day varieties.

Day-Neutral Onions

• Often touted as growing anywhere, day-neutral, or intermediate-day onions, are especially suited to USDA zones 5 and 6. Bred to require 12 to 14 hours of light for bulb formation, day-neutrals can succeed where other onion types do not. "Candy" varieties (Allium cepa "Candy" and vars.) are widely available as plants, giving them a good start on growth in onion-challenging conditions.