The Enigmatic Onion
Article and photos by Chris Doolittle
It’s among the most common of vegetables, ubiquitous in every pantry and an ingredient in thousands of everyday recipes. But for all of its familiarity, the onion is surprisingly misunderstood.
For one thing, it’s usually categorized as a root vegetable, like carrots and potatoes. But it’s actually a bulb, more closely related to a lily than a spud. It’s a member of the Allium family, like garlic and shallots. But unlike those vegetables, its edible bulb forms at the surface of the ground, not below it.
Unlike their Allium cousins garlic and shallots,
onions develop their bulb above ground.
Green onions, or scallions, can be easily grown from “sets,” which are the tiny onions that many garden centers and catalogs offer by the bag in the spring. But don’t be fooled by the pictures of big, juicy onions sometimes used to illustrate those sets. But if you want to grow large onions for storage, you will need to either buy transplants or start your own from seed. That’s because onions are biennials. They produce foliage and an edible bulb the first year, and seed in their second year. Sets are already at the beginning of their second year, and their real job is to make seed. When an onion grown from a set starts to send up a flower stalk, pull it and eat it. The flower stalk extends through the bulb, which will not dry properly for storage.
Many garden centers also sell bundles of transplants, which look like baby green onions, and you can order transplants online. If you choose to start your own from seed, start early! It can take a full 10 weeks to get an onion seedling big enough for transplanting. Since they need to be planted outdoors early – as early as mid-April in northern Nevada – you’ll want to seed them indoors in early February. The seedlings can be moved into individual cells when they are five or six inches tall, and ideally will have three leaves when you transfer them to your garden.
Onions need well-drained soil in full sun. They are shallow-rooted, so they don’t need deep, friable soil, like you’d need for real root crops like parsnips and potatoes. But onions can’t forage far for water or nutrients, so they need ample irrigation, applied close to the plant, and plenty of fertilizer – think ravenous teenager.
Give them their first meal before planting. The ideal starter fertilizer is 10-20-10 at the rate of one-half cup per 20 feet of row. That’s not an easy ratio to find in garden centers, but you can mix triple phosphate (0-46-0) into 10-10-10 fertilizer at the rate of 3.5 oz. to 1 pound and get a close approximation. Follow that up with a side-dressing of ammonium sulfate or other high-nitrogen fertilizer every three weeks through the growing season.
That may sound like a lot of fertilizer, but the ultimate size of an onion depends entirely on the number and vigor of its hollow, spiky leaves. Each of those nitrogen-loving leaves will become a juicy layer in the bulb that will eventually be harvested, so your goal is robust plants with at least 12-14 tall, sturdy leaves. Be sure the onions get at least an inch of water a week, too. Driplines with 6” spacing work well.
Be generous with nitrogen and water to grow tall,
sturdy leaves, and fat, juicy onions will follow.
Don’t plant the transplants deeper than about 1”. They need space above the roots to form their eventual bulb. Because their leaves grow upright, they can be planted close together. You can put transplants as close as two inches apart in double rows that are six inches apart, and pull every other plant for green onions through the growing season.
When selecting varieties of onions to grow, you will need to keep your latitude in mind. Onions are categorized as short-day, long-day, or intermediate, depending on how much day length they need to initiate the bulbing process. Short-day onions will start to mature when daylight length reaches 10 to 12 hours. Long-day onions start to mature when daylight length reaches 14-15 hours. Intermediate varieties will start to bulb when day length is 12-14 hours. Both long- and intermediate-day onions mature in approximately 100 days, so a crop planted in mid-April should be expected to mature by mid-July.
Generally, long-day onions are grown in USDA Zones 6 and below, and short-day onions in Zone 7 and above. Northern Nevada is suitable for either long-day or intermediate varieties. You can also grow short-day onions here, and they will mature faster than they do in the south (75 days rather than 110 days). But they won’t get as large in the north as they do in the south. And they won’t store long, because most short-day varieties are sweet (think Vidalia, Texas Sweet and Maui), which have shorter storage lives.
Three to three and a half months after being transplanted, onion leaves will start to yellow at the tips and the neck will shrink. Eventually the plant will topple over.
As they mature, onion plants draw moisture from
the leaves into the bulb and eventually topple over.
When about half of the onions have fallen over, some growers advise knocking over the remaining plants and cutting off the irrigation water. I prefer to cut the irrigation back but not completely off, and wait until most of the onions fall over naturally. The neck needs to be pretty darn dry if the onion is to cure properly.
After pulling the onions, take them indoors and hang them head down on a rack. Don’t wash them or cut back the tops at this point. The tops need to dry all the way to the bulb to prevent the entry of bacteria that would spoil the onion.
Onions curing on a repurposed seedling rack.
The drying area should be well-ventilated and out of direct sun to avoid scalding the onions. The onions should not touch each other as they dry. When they are completely dry, clip the roots and cut the tops back to one inch. Store in a cool, dry place. Check the onions regularly and use any that are developing soft spots or sprouting.
How long will they store? The sweeter the onion, the shorter the storage life, so use the sweet ones first. Vidalia, Walla Walla and Maui sweet onions (all grown from Yellow Granex transplants) typically have no more than a one-month storage life. Most red onions should be good for three to five months. Yellow onions generally have longer storage lives, and if well cured and properly stored, should be good for eight to 10 months.
Yellow onion varieties have the longest dry storage
life, up to 10 months. And they freeze well, too.
You can also store onions in plastic bags in your freezer – whole or chopped, raw or cooked.
Onion crops should ideally be grown no more than one year in four in the same area to avoid a buildup in blight and viral diseases. Poor drainage can induce rot. Onions can also be troubled by thrips, which attack the leaves, and onion maggots, which are the larvae of the root maggot fly.
