These primitive greenhouses may never be seen at many establishments, and where only cut flowers are grown there is no occasion for them, but to the florist who grows an assortment of bedding plants they are of the greatest assistance. As is well known, there are a number of our soft-wooded plants that grow much faster and thriftier in a hotbed than in the best greenhouse that you can possibly give them.
The vegetable grower starts preparations for his hotbeds in February, but the florist does not need to, and in our latitude the hotbed is of most use from early April on to the end of May, and occasionally during summer, where plants like cyclamen want a little bottom heat.
The frames are usually eighteen.inches at back and twelve inches in front, and for convenience made to fit three or four sashes six feet long and thirty-six inches-wide. When hotbeds are used on a large scale and where drainage is good the earth is excavated to a depth of eighteen inches to two feet, and either boarded or bricked up to a foot above the surface. There is an advantage in this because the late frost does not cool the fermenting material. Wherever you have them, let them be all together, for the larger the mass of manure the slower it will cool.
The first requisite is some good, fresh straw manure, and sometimes that alone is used. If you have some dry leaves of the previous fall you can mix in a third of those, and if you are on good terms with the local brewer the spent hops of the brewery are a splendid material for the purpose. Hops heat violently, and should not be used alone, or the heat will be too violent for a time, and will too quickly subside. I would' call one-half stable manure, one-fourth leaves and one-fourth fresh hops a fine mixture.
You cannot get all your material in one day, but when you have collected enough to begin operations the whole mass, whatever it is, should be turned over once into a big pile and thoroughly shaken out, mixing the long with the short. When the pile begins to show signs of heating, then form your hotbeds.
Lay out a space eighteen inches larger and broader than the frame or frames, and allow for an 18-inch path between the frames, but path and all to be built up with the manure.
Build the sides up square and when making the beds one man should throw on the manure and another be shaking and spreading it evenly and continually tramping on it, so that when it sinks, which it will do as it ferments, it will sink evenly. If the material is dry, have the hose near at hand and every layer of three or four inches give the surface a good sprinkling. It will prevent the heat being so violent, but will make it last longer.
When the bed or material has reached a height of two feet put on your frames and see that they are straight and square or the sash won't fit, and above all see that the frames are not " winding." If you sight across the top edges back and front and they line with each other, then they are not winding. Continue to build up with the material till you are nearly to the top of the frame. Then throw in four or five inches of the plunging material. This could be sawdust, tanbark, or even sifted ashes, but for the sake of the hotbed material for after use, which is invaluable to the plantsman, we prefer to put on four or five inches of some light soil that we have used for some other crop.
Don 't plunge any plants in the soil for five or six days, or till the most violent heat has passed, and keep a little ventilation on to allow the vapor to escape. When the violent heat has subsided get in your plants and the growth they will make will be remarkable. And so will the growth of weeds from the soil. But weeding must be attended to as all other duties.
Only "the man who never forgets" should have the care of the hotbeds. A cold night is often followed by a bright, sunny day, and the sun seems to accelerate the heat of the bed, and if they are neglected till, say 11 a. m., you run a good chance of having your whole crop burned up, which has happened occasionally to most of us. A little ventilation at first, and a little more in an hour, is the way to care for a hotbed. And close down early in the afternoon. With the uniform moisture and heat at the roots and the ammonia-charged atmosphere, the growth of many plants is prodigious.
When hotbeds are started early, about April 1, you should always cover them nightly with mats or shutters, the former much preferred both for warmth and convenience. You must not trust to the bare glass on nights of sharp frost. The surface of the soil gets quickly cool and then Jack Frost touches the plants, whose tops are very near the glass.
The hotbeds are a great relief to us in our crowded state in April and May. And more than that, when the beds are emptied the material is tossed up on a pile and chopped down once or twice during fall, and there you have an excellent substitute for leaf-mold, with some ammonia in it. If not, its mechanical condition is what you want for all of your soft-wooded, and many of the hard-wooded, plants.