In North America, commercial production of celery is dominated by the varieties called Pascal celery. Gardeners can grow a range ofcultivars, many of which differ little from the wild species, mainly in having stouter leaf stems. They are ranged under two classes, white and red. The stalks grow in tight, straight, parallel bunches, and are typically marketed fresh that way, without roots and just a little green leaf remaining.
In Europe the dominant variety of celery most commonly available in trade is Celeriac (Apium graveolens var. rapaceum) grown for itshypocotyl forming a large bulb (commonly but incorrectly called celery root). The leaves are used as seasoning, and the stalks find only marginal use.
The wild form of celery is known as "smallage". It has a furrowed stalk with wedge-shaped leaves, the whole plant having a coarse, earthy taste, and a distinctive smell. The stalks are not usually eaten (except in soups or stews in French cuisine), but the leaves may be used in salads, and its seeds are those sold as a spice. With cultivation and blanching, the stalks lose their acidic qualities and assume the mild, sweetish, aromatic taste particular to celery as a salad plant.
The plants are raised from seed, sown either in a hot bed or in the open garden according to the season of the year, and, after one or two thinnings and transplantings, they are, on attaining a height of 15–20 cm, planted out in deep trenches for convenience of blanching, which is effected by earthing up to exclude light from the stems.
In the past, celery was grown as a vegetable for winter and early spring; it was perceived as a cleansing tonic, welcomed to counter the salt-sickness of a winter diet. By the 19th century, the season for celery had been extended, to last from the beginning of September to late in April.(quote from wikipedia)
