The onion is probably native to southwestern Asia but is now grown throughout the world, chiefly in the temperate zones. Today China, India, the United States, Russia, and Spain are among the leading producers of onions.⁸

 

Some authorities place the onions, garlics, leeks and their relatives in a family of their own, the Alliaceae, and others put them in the lily family, the Liliaceae. There are about 400 species in the genus Allium, including some magnificent ornamentals. Other well known members of the genus include bunching onions (A. fistulosum), chives (A. schoenoprasum), garlic chives (A. tuberosum) and leeks and elephant garlic (A. ampeloprasum).⁹

 

Plant taxonomists have divided the onion species, Allium cepa, into three groups. There is the Cepa Group that includes the typical bulbing onions, which have a single enlarged bulb and are propagated from seeds. The Aggregatum Group includes shallots, multiplier onions, and potato onions, which do not produce seeds and are propagated from lateral bulbs off the main bulb. Lastly, the Proliferum Group includes top-setting onions, walking onions, Egyptian onions and tree onions, which are propagated from bulbils (little "bulblets") borne in the inflorescence.

 

The onion is a biennial herb, usually grown as an annual. All its parts produce a strong onion odor when crushed. It has a superficial root system, a very short flattened stem at the base of the plant, which increases in diameter as growth continues. Leaves are long, linear and hollow. A bulb is formed by thickening of the leaf bases when the plant reaches a certain stage of growth. The fruit is a globular capsule.

 

Bulbing onions have cylindrical, hollow leaves and an enlarged bulb that develops at ground level. The roots come off the bottom of the bulb. The flowers are produced in the second growing season (following a required "rest" period) in a rounded umbel on a stalk 2 to 4 feet tall. The umbels, about 2 in in diameter and consisting of many small purplish flowers, are quite showy.

 

There are two main kinds of onions, based on the day-length required for bulb formation. Short-day varieties start forming an enlarged bulb when days are 12 or 13 hours long; long-day varieties don't form a bulb until days are 14-16 hours long. For both types, bulb enlargement is arrested during hot, freezing or dry weather. Near the equator, where days are 11-13 hours long throughout the year, long-day onions will never form a bulb; and in Canada, where days are 14-20 hours long during the growing season, short-day onions will never form a bulb.¹⁰

 

There are hundreds of onion cultivars, differing in day-length requirement, skin color (white, brown, yellow, red, or purple), size (1 to 6 inches in diameter), shape (globe-shaped, flattened or spindle-shaped), pungency and sweetness. Both pungency and sweetness (which are not mutually exclusive) are determined to a considerable extent by the chemical characteristics of the soil in which the onion is grown. Popular long-day onions are 'Yellow Sweet Spanish', 'Wala Wala' and 'Early Yellow Globe'; popular short-day cultivars are 'Yellow Bermuda', 'Granex', and 'Texas Grano'. The pungent onions are better suited to long-term storage.

 

Vidalia onions are sweet, non-pungent short-day onions (usually 'Granex', 'Texas Grano' or a similar hybrid) that are grown near the town of Vidalia in southeastern Georgia, and whose growers have purchased the exclusive right to use that name. Spring onions or green onions are immature bulbing onions that are used in place of bunching onions (A. fistulosum).

 

Onions grow best in a loose, well-drained soil of high fertility and plenty of organic matter. A constant supply of adequate moisture is necessary for best results. Onions are sensitive to highly acid soils and grow best when the pH is between 6.2 and 6.8.¹¹

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⁸ National Onion Association, “Bring on the Onions! About Onions: Seasonality, Onions for All Seasons and All Tastes" www.onions - usa.org., accessed 05 May 2007.

⁹ The source for this paragraph and the next three paragraphs are take from Randy Sell’s article “Onions— Agronomic Characteristics and Varieties,” NDSU Extension Service, Alternative Agriculture Series, Number 17, August 1993, www.ag.ndsu.edu, accessed 05 May 2007.

¹⁰ The source for this paragraph and the next two paragraphs is from Food that Heal, "Onion— Description and Origin and Cultivation,” www.indiangyan.com, accessed 20 May 2007.

¹¹ Randy Sell, “Onions— Agronomic Characteristics and Varieties,” NDSU Extension Service, Alternative Agriculture Series, Number 17, August 1993, www.ag.ndsu.edu, accessed 05 May 2007.