Plant Frames are generally made of redwood boards one and one-half inches thick. Their dimensions vary, a good serviceable size being six feet long by three feet in width of sash. The frame on which the sash rests should be eighteen inches high on the back and eight inches high in front so that the sash, when in position, will have enough slope to shed off the rain.
A Cool or Cold Frame is one which has no artificial heating.
A Hot Frame is one which is placed on a heap of strawy stable-manure or other fermenting material which has partially spent its heat, its temperature having fallen to about eighty degrees Fahrenheit.
Hot-beds are very useful, especially in Spring, for encouraging rapid growth in tender plants or seedlings, as they supply a warm moist atmosphere very congenial to most of the tender plants. Cuttings also of various plants emit roots and grow much faster on a Hot-bed than when placed where there is only fire heat.
To make up a Hot-bed, secure a quantity of fresh stable-manure and an equal quantity of tree-leaves, which have been recently collected; turn them over and mix them together three or four times every second day for eight days. Build the heap the size and shape of the frame to be used, and allow an extra width of two or three feet all around; spread the mixture evenly in layers of not more than six inches each, treading each layer firmly as spread until the bed is built up about four feet high or thick. Over the surface place a layer of ashes, sand, or leaf-mold, well decomposed, spreading it evenly about three inches thick.
The Hot-bed is now ready for the frame, and after the rank steam has escaped, and the temperature of the air in the frame has fallen to eighty-five degrees Fahrenheit, it is ready for receiving plants, cuttings or seeds. It is well to allow a little ventilation at the top of the frame night and day for a few days, after new beds are put up.
What is meant by Bottom-heat is a bed of sand, ashes or other light plunging material, artificially heated either by hot water or steam pipes, by tanks filled with hot water or by a hotbed made of fermenting material. In this sand or ash-bed the pots or pans or boxes are "plunged," being buried to the rim. Bottom-heat is considered indispensable for propagating by cuttings or seeds in early Spring.