Growing Onions

It’s easy to take onions for granted. The pungent culinary staples are readily available year-round and don’t rank nearly as high on the list of must-grow edibles as succulent summertime tomatoes or tasty wintertime leafy greens.

Yet grow your own, and you may discover subtle new flavor nuances between different varieties. Onions are largely a no-fuss crop and October is an ideal time to plant.

Get yours into the garden before the holidays and, depending on which types you choose, you’ll be ready to harvest in late spring and then again in early summer. Granted, that’s a long season. But since many winter vegetables take little space, such as those tender leafy greens, you’re bound to have room for at least a few rows of onions.

Getting Started

First, it’s important to understand how onions grow.

After planting, onions send down roots and push up green stalks. But they don’t begin swelling into recognizable bulbs until the leaves bulk out and the calendar ticks toward a certain number of daylight hours. Once bulbing does begin, onions typically take 100 to 110 days to reach full size.

Next, onions are categorized as short-day, intermediate-day or long-day.

Those labels have nothing to do with the length of the growing season. Instead, short-day onions respond to 10 to 12 hours of daylight; intermediate-day onions require 12 to 14 hours and long-day onions wait for 14 to 16 hours.

Santa Barbara is endowed with nearly 11 months of 10-hour days, from January 9 to December 2. Twelve-hour days run for about six months, from March 16 to September 25.

But 14-hour days are a meager 69 days, from May 17 to July 25. That’s at least a month short of what long-day onions need to mature. If you do try growing them, you’ll harvest a lot of neck, but very little bulb.

Note that you can also plant a second crop of short-day or intermediate-day onions in mid-spring, for a late-summer harvest. But because fall-planted onions have more time in the ground before bulbing begins, they tend to have larger root masses, resulting in larger onions.

What to Choose

If you like your onions fresh and sweet, short-day Yellow Granex is a winner. The thick, flattish onions that made Vidalia, Georgia, famous are a type of Yellow Granex. Vidalias can only be labeled as such if they are grown in 20 counties in Georgia and meet certain state and federal standards. That Georgia soil is especially low in sulfur (conventional, pungent onions get their heat from sulfur-containing compounds), but you can still grow a very sweet Yellow Granex here.

Other short-day, sweet onions include Red Granex, White Granex, Texas Supersweet, Sweet Georgia Brown and White Bermuda.

Intermediate-day sweet onions include the all-white Super Star, a medium-sized hybrid that’s the only onion to win an All-America Selections award, and Candy, a yellow-skinned, white variety that grows to an impressive 6 inches in diameter. Stockton Red is large, too, while crunchy Italian Torpedo is a long, skinny heirloom.

If conventional pungent onions are more to your liking, look for short-day Red Creole or intermediate-day Cabernet or Mercury.

Grow a few of each variety, and you can have a taste-off at harvest time.

Planting and Care

Choose a spot that receives ample sun year-round. Impeccable drainage with loose, fertile soil that’s at least eight to 12 inches deep is imperative. The maturing bulbs will fill the uppermost four to five inches while their roots will burrow several inches below. Unless you have loamy or sandy soil, grow your onions in containers or raised beds.

Mark a line where you intend to plant. Six inches from each side of the line, dig a trench twice the recommended planting depth of the seeds, sets or transplants. Sprinkle into the trench half a cup of a high phosphorous (10-20-10) granular fertilizer for each 10 feet of row. Mix well-aged compost with what you’ve dug out, fill the trenches with the mix, then plant your onions down the middle.

Keep the soil moist. Once your onions sprout, taper off to watering about once a week, letting any winter rains help out.

If the leaves turn yellow or soft, you’re watering too much. If the soil cracks and the stalks wilt, water more frequently and deeply.

Also apply a mild dose of a high-nitrogen liquid fertilizer every few weeks until about three weeks before your expected harvest.

Harvest

Three to four months after the beginning of January for short-day types, or three to four months after mid-March for intermediate-day types, the stalks should begin to dry out and flop over. That’s your cue that harvest time has arrived.

A mature onion typically bears 13 leaves, with each one corresponding to a ring inside. But even more important is that the tops have entirely toppled.

Use a trowel or cultivator fork to carefully lift out your onions. Spread the bulbs, side by side, stalks and all, on a screen or black plastic garden flat tray. Leave them in the shade for a week or so to cure. Then trim the tops to an inch above the bulbs. Store the bulbs—still in single layers—between sheets of newspaper or screens. Or hang them in mesh bags or nylon stockings. Or leave the stalks attached and braid them, then hang them. Dry, cool air is key. Avoid refrigeration, as the moist air can hasten deterioration.

Sweet onions are best fresh, as they have a high moisture content and typically keep only a month or two. However, the hotter, more pungent varieties can be stored in a dry location for four to six months.