Onions

Onions (Allium cepa) 

The onion is a bulb vegetable and is the most widely cultivated species of the genus Allium.  

The shallot is a biological variety of the onion. Close relatives are garlic, scallion, chive and Chinese onion.

Appearance

The onion plant has a fan of hollow, bluish-green leaves and its bulb at the base of the plant begins to swell when a certain day-length is reached. 

The bulbs are composed of shortened, compressed, underground stems surrounded by fleshy modified scale (leaves) that envelop a central bud at the tip of the stem. 

A bundle of fibrous roots extends from the underside for a short way into the soil. As the onion matures, food reserves accumulate in the leaf bases and the bulb of the onion swells.

Roots, leaves and developing bulb

In the autumn, the leaves die back, and the outer scales of the bulb become dry and brittle, so the crop is then normally harvested. 

If left in the soil over winter, the growing point in the middle of the bulb begins to develop in the spring. New leaves appear, and a long, stout, hollow stem expands, topped by a bract protecting a developing inflorescence. 

The inflorescence takes the form of a globular umbel of white flowers with parts in sixes. The seeds are glossy black and triangular in cross-section. 

In spring, the foliage dies down, and the outer layers of the bulb become more dry and brittle. The crop is harvested and dried, and the onions are ready for use or storage. 

History

The onion plant has been grown and selectively bred in cultivation for at least 7,000 years.

Onions have been described as originating in Iran, Pakistan and Central Asia.

Traces of onions recovered from Bronze Age settlements in China suggest that onions were used as far back as 5000 BC, not only for their flavour but the bulb's durability in storage and transport.

Ancient Egyptians revered the onion bulb, viewing its spherical shape and concentric rings as symbols of eternal life.

Onions were used in Egyptian burials, as evidenced by onion traces found in the eye sockets of Ramesses IV. 

Historians report the use of onions and cabbage in Pompeii and Roman beliefs about the onion's ability to improve ocular ailments, sleep aid, and heal everything from oral sores and toothaches to dog bites, lumbago, and even dysentery.

Varieties

1. Yellow or brown onions are sweeter and are the onions of choice for everyday use in European cuisine, with many cultivars bred specifically to demonstrate this sweetness. Yellow onions turn a rich, dark brown when caramelized and give French onion soup its sweet flavour.
2. Red or purple onions are known for their sharp pungent flavour and are the onions of choice for everyday use in Asian cuisine. They are also used raw and in grilling.
3. White onions are traditional in classic Mexican cuisine and are milder in flavour; they have a golden colour when cooked and a delightful flavour when sautéed.

Growing onions

The onion is most frequently a biennial or perennial plant, but it is usually annual and harvested in its first growing season.

Onions require a high level of nutrients in the soil. 

Onions are categorized into two growing types: long-day and short-day. Long-day onions are named such because they begin sprouting when the days are between 14 to 16 hours in length (late spring/summer), while short-day onions begin sprouting when days are between 10 to 12 hours in length (winter/early spring).

Onions may be grown from seeds or partially developed bulbs called "sets".

Companion planting

Onions have the ability to improve the flavor of their companion plants, as well as deter pests like aphids.

1. Cabbage. Onions will generally work best with Brassicas, members of the cabbage family. Onions are great at repelling insect pests like cabbage worms, cabbage loopers, and cabbage maggots. Broccoli, kale, cauliflower, turnips, kohlrabi, and brussels sprouts are all Brassica vegetables that fare well when planted next to onions, as the onions keep away most of the pests that plague cabbage crops.
2. Carrots. Onions can help repel the dreaded carrot fly. By surrounding your carrot crop with onions, you can keep the garden pest from destroying your carrot harvest.
3. Leeks. While some same-family plants may not work well together, the onion family (also known as alliums) can. Onions and leeks make a good pair due to their similar environmental needs—both require similar nutrients, and leeks are effective at confusing onion flies.
4. Beets. Beets benefit from an onion companion plant. Along with leeks and garlic, onions can be a natural deterrent for certain garden pests, providing protection from insect pests like aphids and sugar beet-flea beetles.
5. Lettuce. Onion has a shorter root depth than lettuce, so these two crops can be planted next to one another without competing for resources, allowing you to maximize the planting space in your vegetable garden.
6. Strawberries. Strawberries are an extremely vulnerable crop to pests. They’re a favorite of aphids, and can be hard to keep free from disease and destruction. Onions help protect the strawberry crop, which can improve the health of your harvest.
7. Tomatoes. The onion’s pungent odor is a great repellent that protects your tomato plants.
8. Swiss chard. The large leaves of the swiss chard can help keep the ground soil moist, providing a ripe environment for the short-rooted onion to grow. Swiss chard can be planted near most members of the allium family (like shallots and chives) for a mutually beneficial relationship.

Non-companions

Peas, pole beans, bush beans, and asparagus don’t grow well when planted near onions.

Cultivation

Select a place with plenty of room and full sunlight. Onions will grow quite large if they're given enough space, so keep in mind that the more area you give them to grow, the larger they will get. Avoid planting them in a shaded location by larger plants or trees.

Onions grow well in raised beds.

Test the soil's pH level and add in any necessary compounds to create a pH that falls between 6 to 7.5.

Testing and altering the pH of your soil is best done at least a month before planting so that any additives have time to take effect on the soil and prepare the foundation for the onions to grow.

When you're ready to plant, until the soil is about 6 inches (15.2 cm) deep, add a layer (1 cup per 20 feet) of phosphorous fertilizer. However, only do this if your soil is low on phosphorus. Be sure to test your soil first to find out. Using a mixture such as 10-20-10 or 0-20-0 will provide an extra boost for your developing onions. At this point, be sure to remove any weeds that may be present in the garden plot you're planting in.

Place your seeds in the holes you've dug, covering them with ¼ to ½ inch of soil. The sets should be no more than two inches deep. Use your hands or shoes to tamp the soil over the top of the onions; they grow better in firm rather than loose soil. Finish up planting by adding a bit of water, and you're set to watch them grow!

Onions are relatively delicate plants, as they have a fragile root system that can easily be damaged or abused by weeds and tugging. Use a hoe to cut off the tops of any weeds that emerge, rather than pulling them out; tugging the weeds could tug out the onions' roots and make growing difficult. Give your onions about 1 inch (2.5 cm) of water per week, and supplement with a nitrogen fertilizer once a month for nutrients. Immediately after planting, add a light layer of mulch between each plant to lock in moisture and block out weeds.

• If you want your onions to taste a bit sweeter, give them more water than you usually would.
• If any of your onions flower, pull them out. These onions have 'bolted' and won't continue to grow in size or flavour.

Onions are fully ripe when the tops appear golden yellow; at this point, bend the tops to lay flat on the ground. Doing this will move further nutrients towards developing the bulb rather than growing the shoots. After 24 hours, the tops appear brown, and the onions are ready to pull. Remove them from the soil and trim off the shoots at 1 inch (2.5 cm) above the bulb and the roots. Leave the onions to dry out for a day or two in the sun, and then move them to a dry space indoors for two to four weeks to continue drying.

• Store onions in stockings or over a wire screen to allow good airflow when drying. This will help them to keep for longer and maintain their flavour.
• Sweet onions will go bad earliest because of their high moisture content, so eat them first to prevent rot from appearing.
• Discard any onions that show signs of decay or cut up and use so they don't spread disease to other onions in storage.

Because onion seeds are short-lived, fresh seeds germinate more effectively when sown in shallow rows, or "drills," with each drill 12" to 18" apart. As the seedlings emerge and crowd each other, they are progressively thinned until the proper distance; usually, 4" to 6", between each plant is attained.

Onion bulbs are produced by sowing seeds in a dense pattern in early summer, then harvested in the autumn when the bulbs are still small, followed by drying and storage. These bulbs planted the following spring grow into mature bulbs later in the growing season.

Routine care during the growing season involves keeping the rows free of competing weeds, especially when the plants are young. The plants are shallow-rooted and do not need much water when established. Bulbing usually takes place after 12 to 18 weeks. 

The bulbs can be gathered when needed to eat fresh, but they are harvested after the leaves have died back naturally if they are stored. 

 It is a biennial plant but is usually grown as an annual. Modern varieties typically grow to a height of 15 to 45 cm (6 to 18 in). 

Culinary

Onions are commonly chopped and used as an ingredient in various hearty warm dishes and may also be used as the main ingredient in their own right, for example, in French onion soup, creamed onions, and onion chutney. They are versatile and can be baked, boiled, braised, grilled, fried, roasted, sautéed, or raw in salads. 

Onions pickled in vinegar are eaten as a snack worldwide.

Onion bulbs used for planting and seeds

In 2019, the world production of onions and shallots (as green produce) was 4.5 million tonnes.

Storage

Cooking onions and sweet onions are better stored at room temperature, optimally in a single layer, in large mesh bags in a dry, cool, dark, well-ventilated location.