Onions! There is no substitute! Bulb onions are valued by cultures all over the world. Not only do they add rich, savory flavor to our culinary endeavors, but they are also a source of potent cancer-fighting phytochemicals.
The Texas sweet onion was designated the official state vegetable by the Texas Legislature in 1997. The first seed, from the Island of Bermuda, was planted in South Texas near the town of Cotulla in 1898.
Onions are photoperiodic, which means they bulb in response to day lengths. It is important for onions to develop strong roots and adequate foliage before the bulbing process begins. Each bulb is made up of layers of leaf sections. As the onion grows, it stores water and carbohydrates in the base of the leaves, which swell to form a bulb. When day length triggers the bulbing response, the larger the onion leaves are up on top, the larger the bulbs will be down below. Long-day varieties require 14-16 hours of daylight, intermediate-day varieties require 12-13 hours, and short-day types require 11-12 hours. Short-day varieties are best for our area. Popular short-day varieties for home gardeners in Texas include: 1015y Texas Super Sweet, Contessa, Yellow Granex, Bermuda, and Red Southern Belle.
Full sun and good bed preparation are important. Onions grow best in well-drained, loose soil that has been amended with 1-2 inches of compost. Form beds that are 4-6 inches high and 20 inches wide in order to provide good drainage. Also, a small amount of 10-20-10 fertilizer applied before planting at a rate of ½ cup per 10 foot row is helpful. Because onions are shallow-rooted, the recommended method to apply pre-plant fertilizer is to dig a trench 4 inches deep and 4 inches wide, sprinkle the fertilizer, cover with soil, and plant a row of onions along each side of the trench. Transplants should be planted knuckle deep (about 1 inch) and 4-6 inches apart down the row. Water as soon as planted. Be sure your plants receive 1 to 1 ½ inches of water each week, preferably from a soaker hose or drip irrigation. Apply a high nitrogen fertilizer every three weeks until onions start to bulb.
Crop rotation, sanitation, and avoiding drought stress will go a long way in preventing onion pests, such as thrips and onion maggots. Rotate all members of the onion family on a three year schedule. Be sure to remove all plant debris at the end of the season. Neem oil, insecticidal soap, and sulfur spray are effective in controlling thrips.
Onions begin to bulb as the days grow longer in spring and reach maturity in May or June. Onion tops do not need to be cut or knocked over; they will do that on their own. The tops provide energy to the bulb, and, if broken prematurely, the onion growth will stop, and the injured neck will become a portal for disease. Once most of the tops have turned yellow and fallen over, pull the onions from the soil and leave them exposed to air and sun for a few days. Then move them to shade to cure for a week or two.
Don not wash. After the leaves have dried, trim the roots and cut the tops to within an inch of onion neck and store in a cool, dry spot.