Greenhouse

a glass house in which plants are grown. The greenhouse has developed from the European notion of training grapevines, fruit trees, and other plants on the sunny side of stone walls, and later, of protecting them by a glass sash. From the covered wall to the lean-to greenhouse is but a short step. Then came the low, extended greenhouses of the florist, the fruit and the vegetable grower. The conservatory, on the other hand, we have developed from a sunny window.

Modern greenhouses are built, both sides and walls, of sash filled with glass. The typical structure is low, but covers a large area. Greenhouses are heated usually by steam or hot water; the latter in pipes or open tanks. Hot air flues are still in use. American commercial greenhouses date from the beginning of the nineteenth century, but were not numerous before the Civil War. At the begining of the twentieth century, according to the official census report, the florists of the United States alone had 68,030,666 square feet of glass surface, not to mention acres of glass under which the young plants are started, or cucumbers, lettuce, tomatoes, pineapples, radishes, onions, asparagus, and other fruits and vegetables are raised for the early market. It costs about fifty cents a square foot of ground area to put up a greenhouse. Florists expect their sales to amount to about a dollar a year per square foot. Vegetable raisers expect a smaller rate, but they are at less expense for labor.

The managing of a greenhouse is a business in itself. How and where to build; the kind of glass to use; right methods of heating, setting, and watering; the right proportion of sand and sod; pruning, forcing, and retarding; the use of slips and of seeds; and many other details may be learned from excellent manuals, but they must be relearned in the school of experience. When all other matters have been mastered fairly well, insect pests, especially plant lice, still remain to plague and weary the grower.