Horticulture is a branch of agriculture concerned with producing fruit, flowers, and vegetables. It can be divided into pomology (growing fruit), olericulture (growing vegetables), and floriculture (growing shrubs and ornamental plants). About 3% of US cropland is devoted to horticulture. It was originally practiced on a small scale, but crops such as the potato and tomato are now often grow in vast fields.
The origins of horticulture lie in the small intensive kitchen gardens of the medieval farming system. The techniques employed include asexual, or vegetative, propagation by leaf, stem, and root cuttings, and by stem and bud grafting. Fruit trees, shrubs and vines, including those bearing apples, pears, plums, cherries, citrus fruits and grapes, are usually propagated by grafting the fruitstock onto a hardier rootstock. In the case of apple trees, the rootstock is usually French crab apple. Plants propagated sexually by seed include some fruits and vegetables, including maize and many other types that produce seed abundantly. Often the seed needs to be overwintered, or stowed at low temperatures and high humidity, before it will begin germination. Seed itself is a major horticultural crop. Close scientific control of pollination is essential for producing crops of specific quality.