If forced vegetables can be made profitable in connection with market gardening, there should be no hesitation in constructing greenhouses. They enable the grower to keep in touch with the market the year round, and they provide employment in the winter when it is often difficult to find sufficient work to keep men busy. Then, again, a greenhouse adds materially to the pleasures of rural or urban life, as it insures summer conditions the year round on some part of the place.
For starting early vegetable plants the greenhouse possesses decided advantages over the hotbed. These may be enumerated as follows: (i) It is cheaper to heat glass structures by means of coal than by manure. (2) Proper soil and atmospheric conditions are better controlled in greenhouses. The gardener spends much of his time inside of the house, and he has abundant opportunity to note every change. If the soil is too dry, it is detected before any injury has been sustained by the plants. If the air is too close, the grower soon discovers it, and the ventilators are opened. (3) Fresh air may be admitted in the severest weather without cold drafts striking the plants. This is impossible in hotbeds. (4) The daily care of greenhouses is less laborious and, therefore, less expensive than in the management of hotbeds. There are no sash to be handled separately several times a day. no mats to move twice a day and no sash to raise when watering. When the Skinner system of irrigation is used in the greenhouse, the labor of watering is so small as to be scarcely worth considering.
Greenhouses are employed for a variety of purposes by market gardeners besides that of forcing crops to maturity. The growing of seedlings for transplanting in cold frames is one of the largest uses. The more tender plants, as tomato, pepper and eggplant, are often transplanted 1 1/2 or 2 inches apart after the seedlings are three to five weeks old. If space permits, any of the vegetable plants may be kept in the greenhouse until time for planting in the open ground. If desirable, they may then be shifted to the cold frame for a short time to harden.