|Species||Allium ampeloprasum L.|
|Cultivar group||Leek Group (other names are used, e.g., Porrum Group)|
|Cultivar||Many, see text|
|Nutritional value per 100 g (3.5 oz)|
|Energy||255 kJ (61 kcal)|
|Dietary fiber||1.8 g|
|Vitamin A equiv.|
|Pantothenic acid (B5)|
|†Percentages are roughly approximated using US recommendations for adults. |
Source: USDA FoodData Central
The leek is a vegetable, a cultivar of Allium ampeloprasum, the broadleaf wild leek (syn. Allium porrum). The edible part of the plant is a bundle of leaf sheaths that is sometimes erroneously called a stem or stalk. The genus Allium also contains the onion, garlic, shallot, scallion, chive, and Chinese onion. Three closely related vegetables, elephant garlic, kurrat and Persian leek or tareh, are also cultivars of A. ampeloprasum, although different in their uses as food.
Historically, many scientific names were used for leeks, but they are now all treated as cultivars of A. ampeloprasum. The name leek developed from the Old English word lēac, from which the modern English name for garlic also derives. Lēac means 'onion' in Old English and is a cognate with languages based on Old Norse; Danish løg, Icelandic laukur, Norwegian løk and Swedish lök. German uses Lauch for leek, but in Dutch, look is used for the whole onion genus, Allium.
Rather than forming a tight bulb like the onion, the leek produces a long cylinder of bundled leaf sheaths that are generally blanched by pushing soil around them (trenching). They are often sold as small seedlings in flats that are started early in greenhouses to be planted as weather permits. Once established in the garden, leeks are hardy; many varieties can be left in the ground during the winter to be harvested as needed.
Leek cultivars may be treated as a single cultivar group, e.g., as A. ampeloprasum 'Leek Group.'  The cultivars can be subdivided in several ways, but the most common types are "summer leeks," intended for harvest in the season when planted, and overwintering leeks, meant to be harvested in the spring of the year following planting. Summer leek types are generally smaller than overwintering types; overwintering types are generally more strongly flavored. Cultivars include 'King Richard' and 'Tadorna Blue.'
Leeks are easy to grow from seed and tolerate standing in the field for an extended harvest, which takes place up to 6 months from planting. The soil in which it is grown has to be loose and drained well; leeks can be grown in the same regions where onions can be grown. Leeks usually reach maturity in autumn. Leeks can be bunched and harvested early when they are about the size of a finger or pencil, or they can be thinned and allowed to grow to a much larger mature size. Hilling leeks can produce better specimens.
Leeks suffer from insect pests, including the thrips species Thrips tabaci and the leek moth. Leeks are also susceptible to leek rust (Puccinia allii).
Leeks have a mild, onion-like taste. In its raw state, the vegetable is crunchy and firm. The edible portions of the leek are the white base of the leaves (above the roots and stem base), the light green parts, and to a lesser extent, the dark green parts of the leaves. The dark green portion is usually discarded because it has a tough texture, but it can be sautéed or more commonly added to stock for flavor. A few leaves are sometimes tied with twine and other herbs to form a bouquet garni.
Leeks are typically chopped into slices 5–10 mm thick. The slices tend to fall apart due to the layered structure of the leek. The different ways of preparing the vegetable are:
Leeks are an ingredient of cock-a-leekie soup, leek and potato soup, and vichyssoise, as well as plain leek soup.
Because of their symbolism in Wales (see below), they have come to be used extensively in that country's cuisine. Elsewhere in Britain, leeks have come back in favor only in the last 50 years, having been overlooked for several centuries.
Raw leek (bulb and lower leaves) is 83% water, 14% carbohydrates, 1% protein, and contains negligible fat (table). A 100-gram (3+1⁄2 oz) reference amount supplies 255 kilojoules (61 kcal) of food energy and is a rich source (20% or more of the Daily Value, DV) of vitamin K (45% DV) and manganese (23% DV). It is a moderate source (10-19% DV) of vitamin B6, folate, vitamin C, and iron (table).
The Hebrew Bible talks of חציר, identified by commentators as leek, and says it is abundant in Egypt. Dried specimens from archaeological sites in ancient Egypt, as well as wall carvings and drawings, indicate that the leek was a part of the Egyptian diet from at least the second millennium BCE. Texts also show that it was grown in Mesopotamia from the beginning of the second-millennium BCE.
Leeks were eaten in ancient Rome and regarded as superior to garlic and onions. The 1st century CE cookbook Apicius contains four recipes involving leeks. Raw leeks were the favorite vegetable of the Emperor Nero, who consumed it in soup or oil, believing it beneficial to the quality of his voice. This earned him the nickname "Porrophagus" or "Leek Eater."
The leek is one of the national emblems of Wales, and it or the daffodil (in Welsh, the daffodil is known as "Peter's leek," Cenhinen Bedr) is worn on St. David's Day. According to one legend, King Cadwaladr of Gwynedd ordered his soldiers to identify themselves by wearing the vegetable on their helmets in an ancient battle against the Saxons that took place in a leek field. The Elizabethan poet Michael Drayton stated, in contrast, that the tradition was a tribute to Saint David, who ate only leeks when he was fasting.
The leek has been known to be a symbol of Wales for a long time; Shakespeare, for example, refers to the custom of wearing a leek as an “ancient tradition” in Henry V. In the play, Henry tells the Welsh officer Fluellen that he, too, is wearing a leek "for I am Welsh, you know, good countryman." The 1985 and 1990 British one pound coins bear the design of a leek in a coronet, representing Wales. One version of the 2013 British one pound coin shows a leek with a daffodil.
Alongside the other national floral emblems of countries currently and formerly in the Commonwealth or part of the United Kingdom (including the English Tudor Rose, Scottish thistle, Irish shamrock, Canadian maple leaf, and Indian lotus), the Welsh leek appeared on the coronation gown of Elizabeth II. Norman Hartnell designed it; when Hartnell asked if he could exchange the leek for the more aesthetically pleasing Welsh daffodil, he was told no.
Perhaps the most visible use of the leek, however, is as the cap badge of the Welsh Guards, a battalion within the Household Division of the British Army.
In Romania, the leek is also widely considered a symbol of Oltenia, a historical region in the country's southwestern part.