Texans love their onions. Of course, we are home to the “Noonday Onion” as well as the 1015Y Texas Super Sweet onion, the “sweetest onion in the world.” And though a native of Pakistan, onions are our state vegetable. Onions are easy to grow if you remember to grow them when the temperatures are cool and the days are short.
Onions are cool-weather plants that “bolt” or bloom when the weather is hot and the days are long. For onion tops to be vigorous, tender, and mild, the weather must be cool. Onions can tolerate frosts but not hard freezes, so they should be planted from bundled bare-root transplants known as “sets” between late January and mid-February. To make large onion bulbs, it’s very important to get them out as early as possible, as late planted onions make small bulbs.
Onions require at least 8 hours of direct sun each day for maximum yields. Like most root crops, they do best in well drained sandy and loamy soils. It is ideal to till in several inches of compost or organic matter and incorporate 2 pounds of a complete lawn (15-5-10, 16-6-12, etc.) per 100 square foot of bed or every 35 feet of row before planting. In smaller plantings use 2 teaspoons per square foot or foot of row. The ideal soil pH for growing onions is 5.5-7.0, so here we generally need to apply lime every few years.
Onions can be grown in raised beds or raised rows 6 inches high, 18 inches wide, and 36 inches apart. Use a stick or hoe handle to poke holes into the soil 1 inch deep. Place the transplants, root side down, into each hole. Gently firm them in and water immediately to settle the soil around them. Onions can also be grown in whiskey barrel (30 gallon) sized containers.
Onions are relatively easy to grow provided they have lots of sunshine, cool temperatures, and regular moisture when forming bulbs. Around 3-4 weeks after planting or when the plants are 6 inches tall, fertilize them with 1 cup of high nitrogen fertilizer (21-0-0, etc.) for each 35 feet of row. Sprinkle half of the fertilizer down each side of the row. Lightly work it into the soil and then water. Be careful not to damage the base of the plants. Hand weeding around them is best. After side-dressing with fertilizer, it is ideal to apply a layer of organic mulch (hay, straw, grass clippings, etc.) to conserve water and prevent weeds. Despite what old timers may have told you, the more foliage your onions make, the larger the bulbs will be when the days start to get longer and the bulbs begin to form. Every leaf forms a ring in the onion.
Green onions for their tops can be harvested at any time. They are most tender when they are small.
Onion bulbs are ready to harvest when the necks of the plants get soft and the tops fall over.
They should be pulled or dug at this point and allowed to cure for several days in a cool dry area. The tops should then be cut off one inch above the onion. This curing process helps them store longer.
Greg Grant is the Smith County horticulturist for the Texas A&M AgriLife Extension Service. He is author of Texas Fruit and Vegetable Gardening, Heirloom Gardening in the South, and The Rose Rustlers. You can read his “Greg’s Ramblings” blog at arborgate.com, read his “In Greg’s Garden” in each issue of Texas Gardener magazine (texasgardener.com), and follow him on Facebook at “Greg Grant Gardens.” More science-based lawn and gardening information from the Texas A&M AgriLife Extension Service can be found at aggieturf.tamu.edu and aggie-horticulture.tamu.edu.