It would scarcely pay to put in a hot water or steam heater for the express purpose of heating hotbeds, for if such an expense were incurred, it would be better to make a forcing-house. Hotbeds may be heated, however, with hot-air flues with very good results. A home-made brick furnace may be constructed in a pit at one end of the run and underneath a shed, and the smoke and hot air, instead of being carried directly upwards, is carried through a slightly rising horizontal pipe that runs underneath the beds. For some distance from the furnace, this flue may be made of brick or unvitrified sewer pipe, but stove-pipe may be used for the greater part of the run. The chimney is ordinarily at the farther end of the run of beds. It should be high, in order to provide a good draft. If the run of beds is long, there should be a rise in the underlying pipe of at least one foot in twenty-five. The greater the rise in this pipe, the more perfect will be the draft. If the runs are not too long, the underlying pipe may return underneath the beds and enter a chimney directly over the back end of the furnace, and such a chimney, being warmed from the furnace, will ordinarily have an excellent draft. The underlying pipe should occupy a free space or pit beneath the beds, and whenever it lies near to the floor of the bed or is very hot, it should be covered with asbestos cloth. While such flue-heated hotbeds may be eminently successful with a grower or builder of experience, it may nevertheless be said, as a general statement, that whenever such trouble and expense are incurred, it is better to make a forcing-house. The subject of forcing-houses and greenhouses is not discussed in this book.
The most satisfactory material for use in hotbed and cold-frame sash is double-thick, second-quality glass; and panes twelve inches wide are ordinarily broad enough, and they suffer comparatively little in breakage. For coldframes, however, various oiled papers and waterproof cloths may be used, particularly for plants that are started little in advance of the opening of the season. When these materials are used, it is not necessary to have expensive sash, but rectangular frames are made from strips of pine seven-eighths inch thick and two and one-half inches wide, halved together at the corners and each corner reënforced by a square carriage-corner, such as is used by carriage-makers to secure the corners of buggy boxes. These corners can be bought by the pound at hardware stores.
Close attention is required in the management of hotbeds, to insure that they do not become too hot when the sun comes out suddenly, and to give plenty of fresh air.
Ventilation is usually effected by raising the sash at the upper end and letting it rest upon a block. Whenever the temperature is above freezing point, it is generally advisable to take the sash off part way, as shown in the central part of Fig. 199, or even to strip it off entirely, as shown in Fig. 197.
Care should be taken not to water the plants at nightfall, especially in dull and cold weather, but to give them water in the morning, when the sun will soon bring the temperature up to its normal state. Skill and judgment in watering are of the greatest importance in the management of hotbeds; but this skill comes only from thoughtful practice. The satisfaction and effectiveness of the work are greatly increased by good hose connections and good watering-pots (Fig. 209).
Some protection, other than the glass, must be given to hotbeds. They need covering on every cold night, and sometimes during the entire day in very severe weather. Very good material for covering the sash is matting, such as is used for covering floors. Old pieces of carpet may also be used. Various hotbed mattings are sold by dealers in gardeners’ supplies.
