Common Name: Onion

General Information

Allium cepa is a herbaceous, perennial plant (usually grown as an annual or biennial in cultivation) producing 4 - 10 leaves about 30cm long and a flowering scape that can be up to 100cm tall from an underground bulb. The plant divides, forming in time a cluster of plants[].
The onion was one of the first plants to be cultivated for food and medicine[]. It is very widely cultivated in most parts of the world for its edible bulb and leaves, there are many named varieties capable of supplying bulbs all the year round[]. This is one of the most cultivated plants in the world, widely grown especially for its edible bulb, but also for its leaves.

Known Hazards

There have been cases of poisoning caused by the consumption, in large quantities and by some mammals, of this plant. Dogs seem to be particularly susceptible[].

Botanical References

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Range

The original habitat is obscure, the plant probably arose in C. Asia (Turkmenistan) - its nearest relative is Allium vavilovii or Allium oschanini

Habitat

Not known in the wild.

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Evergreen Bulb
Height	0.60 m
Pollinators	Bees, Insects
Cultivation Status	Cultivated

Cultivation Details

Onions are best grown in a Mediterranean climate, the hot dry summers ensuring that the bulbs are ripened fully[]. For best growth, however, cool weather is desirable at the early stages of growth[]. Plants are frost-tolerant but prolonged temperatures below 10°c cause the bulb to flower[]. Optimum growth takes place at temperatures between 20 and 25°c[]. Bulb formation takes place in response to long-day conditions[].
Prefers a sunny sheltered position in a rich light well-drained soil[, ]. Prefers a pH of at least 6.5[]. Plants tolerate a pH in the range of 4.5 to 8.3.
Plants are perennial but the cultivated forms often die after flowering in their second year though they can perennate by means of off-sets[].
This species was derived in cultivation from Allium oschaninii[]. Most forms are grown mainly for their edible bulbs but a number of varieties, the spring onions and everlasting onions, have been selected for their edible leaves. There are several sub-species:-
Allium cepa 'Perutile' is the everlasting onion with a growth habit similar to chives, it is usually evergreen and can supply fresh leaves all winter.
Allium cepa aggregatum includes the shallot and the potato onion. These are true perennials, the bulb growing at or just below the surface of the ground and increasing by division. Plants can be divided annually when they die down in the summer to provide bulbs for eating and propagation.
Allium cepa proliferum is the tree onion, it produces bulbils instead of flowers in the inflorescence. These bulbils have a nice strong onion flavour and can be used raw, cooked or pickled. Most modern treatments are now referring to this form as Allium x proliferum, being seen as a hybrid with the Welsh Onion (Allium fistulosum).
Onions grow well with most plants, especially roses, carrots, beet and chamomile, but they inhibit the growth of legumes[, , , ]. This plant is a bad companion for alfalfa, each species negatively affecting the other[].
Members of this genus are rarely if ever troubled by browsing deer[].

Edible Uses

Bulb - raw or cooked. A very versatile food, the bulb can be 10cm or more in diameter and is widely used in most countries of the world. Eaten raw, it can be sliced up and used in salads, sandwich fillings etc, it can be baked or boiled as a vegetable in its own right and is also commonly used as a flavouring in soups, stews and many other cooked dishes. Some cultivars have been selected for their smaller and often hotter bulbs and these are used for making pickles.

Leaves - raw or cooked[, ]. There are some cultivars, the spring onions, that have been selected for their leaves and are used in salads whilst still young and actively growing - the bulb is much smaller than in other cultivars and is usually eaten with the leaves. By successional sowing, they can be available at any time of the year.

Flowers - raw. Used as a garnish on salads. The flowers are somewhat dry and are less pleasant than many other species[].

The seeds are used whole as a spice, especially in Indian cookery[]. They can be sprouted and eaten, and have a delicious onion flavour[].

Medicinal

Although rarely used specifically as a medicinal herb, the onion has a wide range of beneficial actions on the body and when eaten (especially raw) on a regular basis will promote the general health of the body.
The bulb is anthelmintic, anti-inflammatory, antiseptic, antispasmodic, carminative, diuretic, expectorant, febrifuge, hypoglycaemic, hypotensive, lithontripic, stomachic and tonic[, , ]. When used regularly in the diet it offsets tendencies towards angina, arteriosclerosis and heart attack[]. It is also useful in preventing oral infection and tooth decay[]. Baked onions can be used as a poultice to remove pus from sores[].

Fresh onion juice is a very useful first aid treatment for bee and wasp stings, bites, grazes or fungal skin complaints[, ]. When warmed the juice can be dropped into the ear to treat earache[]. It also aids the formation of scar tissue on wounds, thus speeding up the healing process, and has been used as a cosmetic to remove freckles[].

Bulbs of red cultivars are harvested when mature in the summer and used to make a homeopathic remedy[]. This is used particularly in the treatment of people whose symptoms include running eyes and nose[].

Agroforestry Uses:

Onions generally grow well with most plants, especially roses, carrots, celery, celariac, beet and chamomile, but they inhibit the growth of legumes[, , ]. This plant is a bad companion for alfalfa, each species negatively affecting the other[].
Members of this genus are rarely if ever troubled by browsing deer[].

Other Uses

The juice of the plant is used as a moth repellent and can also be rubbed onto the skin to repel insects[].

The plant juice can be used as a rust preventative on metals and as a polish for copper and glass[].

A yellow-brown dye is obtained from the skins of the bulbs[, ].

Onion juice rubbed into the skin is said to promote the growth of hair and to be a remedy for baldness[, ]. It is also used as a cosmetic to get rid of freckles[].

The growing plant is said to repel insects and moles[]. A spray made by pouring enough boiling water to cover 1kg of chopped unpeeled onions is said to increase the resistance of other plants to diseases and parasites[].

Propagation

Seed. Early sowings can be made in late winter in a greenhouse to be planted out in late spring. The main sowing is made in early spring or mid spring in an outdoor seedbed, this bed must be very well prepared. A sowing can also be made in an outdoor seedbed in August of winter hardy varieties (the Japanese onions are very popular for this). These overwinter and provide an early crop of onion bulbs in early summer of the following year.
Onion sets can be planted in early to mid spring. Sets are produced by sowing seed rather thickly in an outdoor seedbed in late spring or early summer. The soil should not be too rich and the seedlings will not grow very large in their first year. The plants will produce a small bulb about 1 - 2cm in diameter, this is harvested in late summer, stored in a cool frost-free place over winter and then planted out in mid spring. A proportion of the bulbs will run quickly to seed but most should grow on to produce good sized bulbs.