By George Boyhan
University of Georgia
The Vidalia onion is a long-season vegetable. Its production begins in September and ends in April or May. If you're thinking about growing your own from seed, now is the time to buy the seed.
Looking in a seed catalog can be confusing when it comes to onions. There are many varieties, but not all are adapted to grow in Georgia. Onions are grouped into three classes, based on their response to day length. There are long-day, intermediate-day and short-day onions.
All onions develop bulbs as the day length increases. But the length of the day when they bulb determines the group they belong to.
Short-day onions begin to bulb when the days are relatively short -- 11 to 12 hours. Intermediate-day onions bulb at 13 to 14 hours, and long-day onions will bulb at 15 or more hours.
Real Vidalia onions
The onions we grow in Georgia are short-day onions. They're sown in the fall and harvested in the spring. Intermediate-day onions are also sown in the fall but are harvested later in June, and long-day onions are sown in the early spring for fall harvest.Seed catalogs may not list onions by day length. But they may use terms like non-storing, overwintering, sweet or mild onions. These are the onions you want. Storage types are long-day onions, and Spanish onions are intermediate-day onions.
Catalogs will often refer to Spanish onions as sweet, but they aren't as mild as the true short-day onions we grow in Georgia.
If you do plant long-day onions by mistake, that's OK. Just harvest them in the winter as green onions. This is what is sold in stores as scallions, which is nothing more than long-day onions grown as a winter crop so they put on a lot of green top but no bulb.
Shape, too
Onions are also classified by color and shape. The true Vidalia onions are yellow, Granex-shaped onions. Granex onions are slightly flattened, not round. These are the mildest onions, particularly when grown in the low-sulfur soils of south Georgia.Commercial growers sow Vidalia onion seed in high-density plantings in late September. These plants are then pulled up and reset to their final spacing in November and December. It's very labor-intensive.
If you plan to direct-seed at the correct spacing for bulbs without transplanting, don't sow your seed in September. Wait until mid-October. This will minimize the formation of seed heads (flowering), which will ruin the onion.
Finally, if you don't want to fool with buying and sowing your own onion seed, you can buy transplants in November and December. Home improvement, feed-and-seed and garden-center stores will often have bare-root onion plants available then.
Transplants are often sold in bundles of about 50 plants. You can plant them in your garden, spacing them about 5 inches apart in the rows and 12 inches between rows.
Follow University of Georgia Extension Service recommendations for fertilization and pest control. Onions are poor competitors with weeds, so you'll have to keep up with your weeding. But the sweet bulbs you'll harvest next spring will be well worth this chore.
(George Boyhan is an Extension Service horticulturist with the University of Georgia College of Agricultural and Environmental Sciences.)
