In horticulture, a vegetable is a herbaceous plant that is edible in whole or part. Parts usually eaten (and representative vegetables) include roots (beet); stems (asparagus); tuber (potato); leaf bases (onion); leaf petioles (celery); entire leaves (cabbage); flower parts (broccoli); immature fruit (cucumber; and mature fruit tomato). Of great importance in the human diet, vegetables are rich in vitamins and minerals and supply fiber and bulk. Some are excellent protein sources when combined with other foods, such as excellent protein sources when combined with other foods, such as beans with rice. They are usually low in calories.
Vegetables are cultured as annuals, with the exception of artichokes, asparagus, cardoon, chives, horse dish, and rhubarb, which are grown as perennials. Propagation is mostly by seed, but artichokes and rhubarb, for example, are propagated by divisions, and Irish potatoes by tubers or tuber sections.
Vegetables are variable in climatic requirements. Temperature and, to a lesser extent, length of day are the climatic components most influential in determining yields. Cool season crops grow best from 12o to 20o (54o to 68o F) and include green peas, lettuce, cabbage, onions, and spinach. Warm season crops grow best from 18o to 20o C (64o to 82o F) and include beans, egg plant, okra, peppers, sweet corn, and tomatoes.
The precise climatic requirements of many crops have resulted in much centralization of production in those areas with suitable climate. An excellent example is the Salinas Valley of California, which, because of ocean cooling, provides ideal conditions for the culture of such cool season crops as lettuce, celery, and broccoli during the summer months.
Rainfall during the growing season was formally required for successful vegetable production. Today almost all commercially grown vegetables are raised under irrigated conditions or with supplemental irrigation. In some areas rainfall during the growing season is considered a detriment because it interferes with operations and promotes plant diseases.
Vegetables are grown on mineral or organic soils.