The age-old experience of farmers is that fruits grown on the protected, sunny side of a slope, mature earliest. This led the way to the development of the modern greenhouse. Some of the early stages of this development may be traced back to England, where it was the general practice to train grapevines upon well-sunned garden walls. Some conceived the idea of inclining these walls so that the rays of the sun might fall more directly upon the vines. Then, in an effort to protect the budding leaves from chilly breezes and sudden frost, glass coverings were built around them. When the warmth from the sun was considered insufficient, flues were placed in back of the wall to furnish additional heat. The resulting lean-to form of greenhouse soon became an independent structure of glass supported by beams of wood and of metal.

Greenhouses were originally used for growing flowers out of season. More recently, greenhouses have been put to other uses. In these glass-covered gardens summer conditions may be maintained at any season of the year. Careful artificial heating is used in addition to the natural warmth of the sun. Smaller greenhouses may be heated more uniformly with hot water. For the larger ones, steam has proven to be more economical and practical. In a greenhouse, ventilation is Just as important as heating. The regulation of the air supply is essential in controlling temperature and humidity. It is vital to avoid sudden changes in either.

The commercial advantages of greenhouses gardening can readily be seen. If a gardener can force the growth of his vegetables several months in advance of the regular season, he can compete with the produce shipped from southern climates. He can also send some of his crops to market before those in his locality have matured.