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Wednesday, Nov. 18, 2009

Grow sweet onions in winter vegetable garden

The peach is Georgia’s state fruit, and the brown thrasher is the state bird. Georgia also has a state shell (knobbed whelk), a state insect (honey bee) and a state reptile (gopher tortoise). But what is the state vegetable?

The answer is — the Vidalia onion. This mild, sweet onion is a southern favorite, and with special care, we can grow them in Middle Georgia.

There are many types of sweet onions, but the Vidalia is one of the best. Sweet onion growers control plant varieties, fertilization and other factors to control the flavor of the onion.

We call these sweet onions, but onions actually have two major flavors. Sugars make them sweet, but pungent chemicals make the onions hot. A sweet onion has enough sugar to make it sweet, but more importantly, it has a low level of the pungent flavor chemicals.

The most important factor in making sweet onions sweet is having low levels of these pungent compounds.

The levels of these pungent chemicals in the onion are controlled by the variety of onion grown, how they are grown and the amount and timing of sulfur fertilization given to the plant.

Sweet onions grow best on sandy soils. Till the area well, mixing in fertilizer and lime as needed. Proper fertilization is a big key to growing sweet onions. Over-fertilization or late fertilization with sulfur makes onions hot. However, sulfur is essential for plant growth, so we cannot leave it out of our fertilizer. Use fertilizers containing sulfur through January. After Jan. 31, use fertilizers without sulfur.

At planting — around Nov. 25 — incorporate 1 1/2 pounds of 5-10-15 or 10-10-10 per 100 square feet of garden. Side-dress lightly 30 days and 60 days after planting with three-quarters pound of the same fertilizer per 100 square feet. Try to select fertilizers that contain from 4 percent to 8 percent sulfur. Read the back of the bag to check sulfur content.

After Jan. 31, change to fertilizers that contain no sulfur.

These include calcium nitrate, potassium nitrate or Bulldog soda (sodium nitrate). Apply three quarters pound of these per 100 square feet every four to five weeks until March 15.

These last fertilizers can be hard to find, so call area garden centers, farm supply stores and hardware stores to see if they stock one of these. If you cannot find these fertilizers, you can use ammonium nitrate to side dress, but only apply one-half pound per 100 square feet.

Variety makes a lot of difference, so buy Vidalia onion transplants. You can perhaps find them in the Farmers and Consumers Market Bulletin. Call (800) 282-5852 to subscribe.

The onions grown as Vidalias are a Granex variety — a flat, mild onion that does not store well. Plant transplants 1 to 2 inches deep in November or December. Water plants well soon after transplanting and then as needed to keep the soil from drying out. Mulch around onions to prevent weeds.

Onions begin to bulb as the day length increases in the early spring. Keep them well-watered at this time. They may need up to 1 3/4 inches of water each week at this time. Proper watering may help keep the onions sweet.

As the onions mature, the onion necks will begin to get soft, and tops will begin to bend or fall over — probably in April or early May. Harvest the entire onion plant. Let the plant dry well in a dry, slightly shaded spot. The onions will be ready to store when the onion necks are dry all the way to the interior. Then clip the tops off and store onions in a cool, dry spot. Vidalia onions will not store well, so use them quickly. Storing them in the refrigerator may prolong their life, but onions stored for a long time will begin to get more pungent.

Fall and winter does not have to put an end to the vegetable patch. You also can transplant broccoli, collard, cabbage, Brussels sprouts and kale, or try vegetables like elephant garlic, asparagus or rhubarb.

For more information, contact your local extension office.

Willie Chance is retired from UGA Extension in Houston County. To reach your local extension office, call (800) ASK-UGA1 from any non-cell phone. To subscribe to the central Georgia home gardening newsletter, e-mail mg@uga.edu. Also see www.gaurbanag.org.