“I will not move my army without onions!”
–General Ulysses S. Grant, 1864
The commander of the Union army during the Civil War reportedly believed that the tasty bulbs would help treat dysentery, powder burns and other ailments.
But onions have been an indispensable ingredient in cuisines throughout the world for much longer. Native to Asia and the Middle East, onions have been cultivated for more than 5,000 years.
They grow well in many places, including here on the Central Coast — provided you select the right kind. Plant your onion seeds, sets or seedlings during the next few weeks, and you’ll be ready to harvest next spring.
It’s All About Day Length
Mesh bags of onion sets are fine if all you want to do is grow green onions.
But full-size onions are quite sensitive to day length as they mature. As such, breeders have divided them into three groups: short-day onions start the bulbing process with 10 to 12 hours of daylight; intermediate-day onions start with 12 to 14 hours of daylight; and long-day onions don’t kick into gear until 14 to 16 hours of daylight.
Don’t even consider growing those long-day onions. They’re designed for northern latitudes where gardeners have to wait until their ground thaws in the spring before they can plant; and then their peak summer days stretch far longer than ours.
Instead, short-day and intermediate-day onions are best for us, and we can plant them twice a year: in late October or November for a late-spring harvest, and in spring for a late-summer crop. Fall planting, however, yields more robust bulbs. The earlier you plant, the bigger they’ll get.
Onions start their life by pushing up green stalks and sending out shallow roots. That’s about all that happens until lengthening daylight and warmer temperatures trigger the bulbs to begin swelling.
On the Central Coast, short-day onion bulbs planted in the fall should begin to swell right after the first of the year. For example, January 11 is the first day with 10 hours of daylight, while March 17 marks 12 hours of daylight. So by early spring, the bulbs are well on their way.
Intermediate-day onions won’t start swelling here until mid-spring, but should still grow well. But plant a long-day onion, and there won’t be enough 14 hours-plus days to produce a full-size bulb. Instead, you’ll just get a lot of neck.
Choose an area in full sun, even over winter. Onions like crumbly, reasonably fertile soil with good drainage. Cold, continuously wet soil is likely to rot out the bulbs — if you even get that far. Too soaked, and the seeds might not sprout.
Sandy soils won’t need much work. But if you have heavy clay, amend heavily with rough-textured compost and gypsum, or plant your onions in lighter soil in a raised bed or container.
Whatever your soil, dig a trench 8 to 12 inches deep for each row and break up any dirt clods. Space your rows a foot apart and sprinkle a high-phosphorous (10-20-10) granular fertilizer into the bottom of each trench. Mix a generous dose of well-aged compost into the soil that you’ve excavated. Then shovel it back into the trench, and plant your seeds, sets or seedlings at their recommended depth.
Finding short-day sets or seedlings may be difficult. You can start seeds in flats first, but they are easier to sow directly into the garden.
Sow the seed fairly thickly. Then when you see the first sprouts, start thinning. Toss those thinnings into salads or soups, or use them as seasoning. Have as a goal a spacing of at least 4 to 5 inches for regular short-day types, and 5 to 6 inches for larger varieties.
However, if you do start your seeds in flats, wait until their stalks are the thickness of a pencil and have three to four leaves before transplanting. Also know that bigger is not better. Moved with more than five leaves, the seedlings may not perform properly in the ground.
In the garden, transplants may stall for a week or two. Don’t worry — they’re busy rooting out. Once established, they should begin sending up new leaves every couple of weeks.
Water regularly to keep the soil moist, but not soggy. If the leaves turn yellow or soft, reduce watering. Also apply a mild dose of a balanced, liquid fertilizer every few weeks until the bulbs swell to twice the diameter of their necks. Brush back the soil to check their progress.
Keep the area weed-free. Onions don’t like to compete with other plants for nutrients and moisture.
A well-grown, full-size onion has about 13 leaves, with the number of leaves corresponding to the number of rings inside.
But more important than counting the leaves is watching what they do. Three to four months after they emerge from the earth, the leaf stalks should begin to yellow and flop. No longer a watering issue, the yellowing signals that it’s time for harvest.
Let the tops topple. Once they’re completely down, use a cultivating fork or trowel to gently lift out the bulbs. Yank on the dried stalks and they may break in your hand, leaving the bulbs in the ground.
Cure your onions by spreading them on dry dirt or on a screen for a few days. If it’s especially hot and sunny, dry them in the shade to prevent sun scald. Provide good air circulation and make sure that the bulbs don’t touch.
After curing, trim the tops to an inch above the bulbs. Store your onions between layers of newspaper or screens. Or keep the stalks and braid them, then hang the onions. Either way, keep your onions in a cool, dry place. Avoid the refrigerator, where the moist air can cause the bulbs to deteriorate faster.
However, sweet onions are best fresh. They are already composed of a high percentage of moisture, and don’t typically keep beyond a month or two.
Onions for the Central Coast
Sweet onions dominate the short-day category.
Yellow granex is perhaps the most famous, because when it’s grown in certain counties in Georgia, it’s allowed to be called a Vidalia onion. Grown anywhere else, including the Central Coast, it may be just as sweet. But it has to be called a yellow granex, rather than a Vidalia.
Other short-day onions include yellow Texas Early Grano, yellowish-white Texas Supersweet, greenish-white White Bermuda and the very white Contessa.
Intermediate-day onions include Stockton Red, yellowish-white Candy and all-white Super Star, which is the only hybrid onion to win an All-America Selections award. It’s huge, weighing in at 1 pound or more.
Also look for Italian Torpedo Red Bottle, an heirloom onion that is sweet, crunchy and skinny, and measures 2 to 3 inches wide and up to 6 inches long.
Seeds of Wisdom
If growing full-size onions tests your patience, grow green or bunching onions from onion sets instead.
The slender, tasty onions are ready for harvest in less than half the time. They can be planted year-round.
And ringing a bed of broccoli during winter, they will help to deter aphids.
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