Onion – October Plant of the Month

It's hard to imagine a kitchen without onions! While onions may not be the first vegetable that springs to mind when we think of nutritional benefits, they are a good source of Vitamin C, a number of healthful antioxidants, and dietary fiber -- all for very few calories. For the most nutritional benefits from onions, let them sit for 5 minutes after slicing or chopping before using.

Botanically speaking, onions are tunicate bulbs, with a papery “tunic” that covers the bulb and helps to keep its fleshy scales from drying out. These scales are actually leafy structures, so when you eat onions you are eating leaves!

VARIETIES

Onion varieties come in a variety of colors – white, yellow, and red. Yellow onions generally are pungent, keep well, and are a good choice for cooking. White and red varieties are generally less pungent than yellow and may be eaten raw or cooked. Sweet onion varieties, such as Walla Walla and Vidalia, are large and mild. They don’t store well and can be enjoyed raw or cooked.

Success with onions starts with choosing the right type of onion for your latitude. Daylength is the signal that tells most onions when it's time to stop growing vegetatively -- putting energy into forming new leaves -- and time to start forming a bulb. Long day varieties of onions need exposure to 14 to 16 hours of daylight to bulb up. (We refer to day length, but it’s actually the length of the night that the plants are responding to.) These onions grow well north of 35 degrees latitude, or approximately above a line drawn through northern North Carolina, Oklahoma, Arizona to central California. These are the onions that are grown for summer harvest in the northern half of the country. They are planted in early spring, putting on vegetative growth until the lengthening days of early summer trigger bulb formation. Many varieties of long day onions have a pungent flavor and store well. 'Yellow Sweet Sandwich' and ‘Walla Walla’ are long day sweet varieties.

South of 35 degrees latitude, with its shorter summer daylengths, gardeners should grow short day onion varieties, ones that form bulbs when the days are 10 to 12 hours long. Short day onions are planted in the fall in the south and grown through the winter for spring harvest or sown in very early spring. Because of their higher water content, most short day onions do not store well and are best for fresh eating. Some well-known short day sweet onions include 'Vidalia', 'Giant Red Hamburger', and 'Texas Supersweet'

If a northern gardener planted short-day onions, they would be exposed to enough daylight hours to initiate bulb formation so early in the season that big bulbs would never have the chance to form. And if a southern gardener planted a long-day variety, the onions would never be exposed to sufficiently long days to cause bulbs to form.

Modern plant breeding has produced intermediate, or day neutral, onion varieties. These varieties aren't as sensitive to daylength and bulb up well in response to 12 to 14 hour days. They grow well across a broad range of the country. Intermediate day onions are usually planted in the spring. 'Candy' is a widely adapted sweet intermediate day onion.

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Site: Full sun and fertile, well-drained soil. Onions are a good crop for raised beds, which generally dry out and warm up earlier in spring than in-ground beds, allowing for earlier planting.

When to Plant: Southern and Southwestern gardeners in mild winter areas can plant short day onion seeds in the fall for harvest the following spring or set out short-day transplants in late winter to early spring. In spring, gardeners in all areas can direct-seed onions as soon as the soil can be worked in the spring. Or start seeds early indoors 8-10 weeks before planting outside; set out hardened-off homegrown or purchased transplants 2-4 weeks before the last frost date.

Onions can also be started from sets, or small, immature bulbs, set out in early spring about 2-4 weeks before the last frost date. Sets give you an onion harvest sooner than planting from seed, but the selection of varieties available is much fewer than with seed.

Planting: Plant seeds directly in the garden ¼ deep and ½ inch apart. When plants are a few inches tall, thin to 4 inches apart for larger bulbs; 2 inches apart for smaller ones.

When starting seeds early indoors, sow in flats at the same spacing, but don’t thin. If indoor seedlings begin to get droopy, trim them back with sharp scissors to 3 inches. Harden off before planting in the outdoor garden 2-4 weeks before the last frost date. Space transplants 2-4 inches apart, depending on desired bulb size. Make sure transplants are smaller in diameter than a pencil to lessen the chances of bolting, or going to seed prematurely.

When planting sets, chose bulbs that are no bigger than ½ to ¾ inch in diameter. Larger sets tend to bolt or go to seed quickly. Place sets with the pointed end up about 1 inch deep, so they are just covered with soil.

Culture: Onions are shallow-rooted and do best with consistent soil moisture. They also don't compete well with weeds. A 3-4 inch deep layer of organic mulch will help retain soil moisture, keep weeds down, and avoid the damage to onion roots that might occur when weeding.

Troubleshooting: Onions are generally a pretty trouble-free crop. One pest you might encounter is the onion maggot, a small white fly larva that feeds on the developing bulbs. Rotate the location of Onion family crops in the garden and cover the onion bed with a lightweight floating row cover to keep adult flies from laying eggs. Thrips are tiny insects that feed by sucking out the juices on onion leaves, causing them to turn stippled and silvery in color and stunting bulb size. To control thrips, knock them off the leaves with a strong spray of water repeated several times daily. For severe infestations, spray with an insecticide labelled for thrips, such as insecticidal soap, neem oil, or spinosad, following all label instructions.

Harvesting: Onions are ready to dig when their tops begin to yellow and fall over. When the tops are browned, carefully dig the onions and let them dry in a well-ventilated spot out of direct sun for a couple of days. If you plan to store onions, let them dry until their tops are completely brown and their outer skins are papery. Then store in a cool, dry, dark location.

SCALLIONS

Also called green or bunching onions, these onions don't form bulbs. Their green tops and blanched below-ground sections are used fresh, both raw and cooked. Scallions may be bulbing onion varieties that are simply harvested when young or they may be different species that never produce bulbs. 'Evergreen White Bunching' is a very hardy, non-bulbing scallion variety that can be planted in early spring for summer harvest or in late summer or early fall to overwinter. Protect with mulch in northern areas over the winter.

Sow seeds, transplants, or sets for scallions as you would for bulbing onions, but space or thin to only an inch apart. Begin harvesting as soon as the tops are 6-8 inches tall. The more mature the plants, the stronger their flavor. Clumps of the winter hardy varieties can be divided their second summer to produce a new crop.

FUN FACTS

  • Who eats the most onions? According to the National Onion Association, Libya has the highest per capita onion consumption in the world – 66.8 pounds of onions per person per year! (Per capita consumption in the U.S. is 20 pounds.)
  • Why does chopping onions make you cry? When onion cells are cut, enzymes that were kept separate in the intact cells mix together and produce volatile sulfur compounds. When these gases reach your eyes they mix with your tears to form sulfuric acid – ouch! Your eyes then make more tears to try to wash the irritant away. Cooking inactivates the enzymes, which is why only raw onions have this tearful effect. Chilling an onion before slicing helps to slow the enzyme activity down, making onion chopping a little more comfortable. Also the root end of the onion contains the most sulfur compounds, so chop this end last. Onions that store well have the highest sulfur levels and are more pungent, while milder sweet onions that don’t keep as well are lower in sulfur and less tear-producing.

Check out this recipe for Libyan Couscous bil Busla (couscous with onion topping).