Allium cepa

An evergreen bulb growing to 60cm at medium rate, hardy to UK zone 5 and not frost tender. Flowers June to July; hermaphroditic and self-fertile. Attracts wildlife. Prefers light to medium well-drained soils, thrives in mildly acid to very alkaline pH, and requires full sun and moist soil.

Description

An onion family plant. A herb with a two year life cycle. Normally it develops fattened bulbs at the base. It has a shallow fibrous root system. The actual stem in very short and condensed. Leaves are produced in an alternate fashion one after the other from the top of this stem. Successive leaves grow up inside, then burst through the leaf sheath of the previous leaf. Leaves are thin and long. They are slightly to markedly flattened on the upper surface. Long day lengths and warm temperatures help the leaf bases become swollen and store food reserves. Flowers are greenish white in colour. Flowers develop on a rounded head with stalks all coming from the centre. Flowers in the rounded head open irregularly. There are no bulbils on the flower-head. There are short day cultivars that will form bulbs in the tropics.

Edible Uses

The bulb is eaten raw or cooked and is one of the most widely used vegetables in the world, growing 10cm or more in diameter. Raw, it can be sliced into salads or sandwich fillings; it is also baked or boiled as a vegetable in its own right, and commonly used to flavour soups, stews, and countless other cooked dishes. Some cultivars are selected for smaller, hotter bulbs specifically suited to pickling. Leaves of spring onion cultivars are harvested while young and actively growing for use in salads; the bulbs of these types are small and typically eaten along with the leaves. Successional sowing makes leaves available year-round. Flowers are eaten raw as a salad garnish, though they are somewhat dry and less pleasant than those of many related species. Seeds are sprouted and eaten, with a delicious onion flavour. Nutritional values per 100g fresh weight: 72 calories; water 79.8%; protein 2.5g; fat 0.1g; carbohydrate 16.8g; fibre 0.7g; ash 0.8g; calcium 37mg; phosphorus 60mg; iron 1.2mg; sodium 12mg; potassium 334mg; thiamine (B1) 0.06mg; riboflavin (B2) 0.02mg; niacin 0.2mg; vitamin C 8mg.

Traditional Uses

The bulbs and leaves are used as flavouring raw or cooked. The flowers are crushed and eaten.

This uses section is brief — help expand it

Medicinal Uses

Though rarely used as a dedicated medicinal herb, the onion offers a broad range of beneficial effects and promotes general health when eaten regularly, especially raw. The bulb is anthelmintic, anti-inflammatory, antiseptic, antispasmodic, carminative, diuretic, expectorant, febrifuge, hypoglycaemic, hypotensive, lithontripic, stomachic, and tonic. Regular dietary use helps offset tendencies toward angina, arteriosclerosis, and heart attack, and is useful in preventing oral infection and tooth decay. Baked onions can be applied as a poultice to draw pus from sores. Fresh onion juice is an effective first-aid treatment for bee and wasp stings, bites, grazes, and fungal skin complaints. Warmed juice dropped into the ear relieves earache. Onion juice also aids scar tissue formation on wounds, speeding healing, and has been used cosmetically to reduce freckles. Bulbs of red cultivars, harvested when mature in summer, are used to prepare a homeopathic remedy particularly suited to symptoms including running eyes and nose. The German Commission E Monographs approve onion for appetite loss, arteriosclerosis, dyspeptic complaints, fevers and colds, cough and bronchitis, hypertension, tendency to infection, inflammation of the mouth and pharynx, and the common cold.

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. Hand eczema may occur with frequent handling. May interfere with drug control of blood sugar.

Distribution

A temperate plant. It is more easy to get onions to grow and form bulbs in the highlands in the tropics but they can be grown from sea level to 2600 m altitude in Papua New Guinea. In Nepal they grow to 3000 m altitude. They do not suit the wet humid tropics. Because the day lengths are short near the equator, onions often do not produce a bulb. Some newer varieties will yield in the tropics. It plant grows best at 12-21°C and the bulb forms best at 15-25°C. It grows best with a pH 5.7-6.6. It suits hardiness zones 5-10.

Where It Grows

Afghanistan, Africa, Albania, Amazon, Andorra, Angola, Argentina, Armenia, Asia, Australia, Austria, Azerbaijan, Balkans, Bangladesh, Benin, Bolivia, Brazil, Britain, Brunei, Burkina Faso, Cambodia, Canada, Cape Verde, Caucasus, Central Africa, Central America, Central Asia, China, Colombia, Congo, Cook Islands, Costa Rica, Côte d'Ivoire, Cuba, East Africa, East Timor, Ecuador, Egypt, Europe, Fiji, Finland, FSM, Gabon, Georgia, Ghana, Greece, Guam, Guyana, Haiti, Hawaii, Himalayas, India, Indochina, Indonesia, Iran, Iraq, Ireland, Italy, Ivory Coast, Jamaica, Japan, Jordan, Kazakhstan, Kenya, Korea, Kyrgyzstan, Lithuania, Macedonia, Madagascar, Malawi, Malaysia, Marshall Islands, Mediterranean, Mexico, Micronesia, Middle East, Moldova, Myanmar, Nauru, Nepal, Netherlands, Nicaragua, Niger, Nigeria, North Africa, North America, Northeastern India, Pacific, Pakistan, Papua New Guinea, PNG, Peru, Philippines, Pohnpei, Poland, Romania, Russia, Sahel, Saudi Arabia, Scandinavia, SE Asia, Senegal, Serbia, Sikkim, Slovenia, Somalia, South Africa, Southern Africa, South America, South Korea, Spain, Sri Lanka, Sudan, Switzerland, Tajikistan, Tanzania, Tasmania, Thailand, Timor-Leste, Tonga, Turkey, Türkiye, Uganda, Ukraine, Uruguay, USA, Uzbekistan, Vanuatu, Vietnam, West Africa, West Indies, Zambia, Zimbabwe,

Cultivation

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. 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. Plants are perennial but the cultivated forms often die after flowering in their second year though they can perennate by means of off-sets. 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 species was derived in cultivation from A. 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. 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. Alliums are typically harvested in late spring to early summer, when the bulbs mature and the tops begin to yellow. Allium species typically flower in late spring to early summer, depending on the species and local climate conditions. Allium species generally have a moderate growth rate, with bulbs typically taking about 100 to 150 days from planting to harvest, depending on the variety and growing conditions.

Propagation

Early sowings can be made in February in a greenhouse for planting out in late spring. The main sowing is in March or April in a well-prepared outdoor seedbed. A further sowing of winter-hardy varieties (Japanese onions are widely used for this) can be made outdoors in August; these overwinter and produce bulbs in June of the following year. Onion sets can be planted out in March or April. Sets are produced by sowing seed thickly in an outdoor seedbed in May or June on soil that is not too rich — seedlings will remain small in their first year, producing bulbs of about 1–2cm diameter. These are harvested in late summer, stored in a cool, frost-free place over winter, and planted out the following April. A proportion will bolt to seed but most should develop into good-sized bulbs.

Other Uses

Plant juice acts as a moth repellent and can be rubbed onto the skin to repel insects. The juice also serves as a rust preventative on metals and as a polish for copper and glass. A yellow-brown dye is obtained from the dry outer skins of the bulbs. Rubbing onion juice into the scalp is said to promote hair growth and act as a remedy for baldness, and it is also used cosmetically to reduce freckles. The growing plant is said to repel insects and moles. A spray made by covering 1kg of chopped unpeeled onions with boiling water is said to increase the disease and parasite resistance of other plants when applied to them.

Other Information

In Papua New Guinea, it is not widely grown but is popular and imported for sale. It is a commercially cultivated vegetable.

Notes

There are about 300-700 Allium species. Most species of Allium are edible (Flora of China). All alliums are edible but they may not all be worth eating! They have also been put in the family Alliaceae.

Nutrition

Synonyms

Also Known As

Albasa, Anyezi, Basal, Bawang, Besalim, Butungulu, Cebola, Cebolla, Cebula, Chivannaulli, Cibule, Cipolla, Dungari, Irulli, Kanda, Kuchen zweibel, Kywtthun-ni, Luk, Mangafaka, Nirulli, Oignon, Palandu, Piaja, Piyaz, Pyaj, Pyanj, Pyaz, Sogan, Sybo, Talap, Tamanegi, Tongolobe, Tschong, Ulligaddalu, Ullikadalu, Vengayam, Yang cong, Yangpa

References (91)

• Ali, A. M. S., 2005, Homegardens in Smallholder Farming Systems: Examples from Bangladesh. Human Ecology, Vol. 33, No. 2 pp. 245-270
• Ambasta S.P. (Ed.), 2000, The Useful Plants of India. CSIR India. p 28
• Anderson, E. F., 1993, Plants and people of the Golden Triangle. Dioscorides Press. p
• Ara, R. I. T., 2015, Leafy Vegetables in Bangladesh. Photon eBooks. p 46 f
• Badwar, R. R., & Fernandez, R. R., 2011, Edible Wild Plants of the Himachal Pradesh State by IHBT, Himalayas, Daya Publishing House,. Delhi, India

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