[size=75]From Wikipedia, the free encyclopedia [/size]
Horseradish (Armoracia rusticana, syn. Cochlearia armoracia) is a perennial plant of the Brassicaceae family, which includes mustard and cabbages. The plant is probably native to southeastern Europe and western Asia, but is popular around the world today. It grows up to 1.5 metres (five feet) tall and is mainly cultivated for its large white, tapered root.
The horseradish root itself has hardly any aroma. When cut or grated, however, enzymes from the damaged plant cells break down sinigrin (a glucosinolate) to produce allyl isothiocyanate (mustard oil), which irritates the sinuses and eyes. Once grated, if not used immediately or mixed in vinegar, the root darkens and loses its pungency and becomes unpleasantly bitter when exposed to air and heat.
Horseradish was cultivated in antiquity. According to Greek mythology, the Delphic Oracle told Apollo that the horseradish was worth its weight in gold.[verification needed] Horseradish was known in Egypt in 1500 BC and has traditionally been used by Jews in Passover Seders.  Cato discusses the plant in his treatises on agriculture, and a mural in Pompeii showing the plant has survived until today. Horseradish is probably the plant mentioned by Pliny the Elder in his Natural History under the name of Amoracia, and recommended by him for its medicinal qualities, and possibly the Wild Radish, or raphanos agrios of the Greeks.[verification needed]
Both root and leaves were used as a medicine during the Middle Ages and the root was used as a condiment on meats in Germany, Scandinavia, and Britain. It was brought to North America during Colonial times.
William Turner mentions horseradish as Red Cole in his “Herbal” (1551-1568), but not as a condiment. In “The Herball, or Generall Historie of Plantes” (1597), John Gerard describes it under the name of raphanus rusticanus, stating that it occurs wild in several parts of England. After referring to its medicinal uses, he says: “the Horse Radish stamped with a little vinegar put thereto, is commonly used among the Germans for sauce to eate fish with and such like meates as we do mustarde.”[verification needed]
Horseradish is perennial in hardiness zones 5 - 9 and can be grown as an annual in other zones, though not as successfully as in zones with both a long growing season and winter temperatures cold enough to ensure plant dormancy. After the first frost in the autumn kills the leaves, the root is dug and divided. The main root is harvested and one or more large offshoots of the main root are replanted to produce next year’s crop. Horseradish left undisturbed in the garden spreads via underground shoots and can become invasive. Older roots left in the ground become woody, after which they are no longer culinarily useful, although older plants can be dug and redivided to start new plants.