Those which are mostly used in the kitchen garden, are made with new horse-dung, or with tanners' bark, in the following manner: take a quantity of new horsedung, in which there should be some litter or straw, but not in too large a proportion: the quantity of this mixture must be, according to the length of bed intended, which, if early in the year, should not be less than a good load for each light. This dung should be thrown up in a heap, mixing it with some seacoal ashes, which will help to continue the heat: it should remain six or seven days in this heap, then it should be turned over, and the parts well mixed together, and cast into a heap again, where it may continue five or six days longer, by which time it will have acquired a due heap; then in some well sheltered part of the garden, a trench should be dug out, in length and width proportionable to the frames intended for it; if the ground be dry, about a foot , or a foot and a half deep; but, if wet, not above six inches; then the dung should be wheeled into the opening, and every part of it stirred with a fork, to lay it exactly even and smooth through every part of the bed; as also, to lay the bottom of the heap (which has commonly less litter) upon the surface of the bed, this will prevent the stream [sic] from rising so plentifully as it would otherwise do.

Farther to prevent this, and the heat from rising so as to burn the roots of whatever plants may be put into the ground, it will be a good way to spread a layer of neat's dung all over the surface of the horse dung. If the bed be intended for cucumbers or melons, the earth should not be laid all over the bed at first; only a hill of earth should first be laid in the middle of each light, on which the plants should be planted, and the remaining space should be filled up from time to time, as the roots of the plants spread; but if the hotbed be intended for other plants, then, after it shall have been well prepared, it should be left two r three days for the steam to pass off before the earth is laid over.

Always observe to settle the dung close with a fork; and if it be pretty full of long litter, it should be trodden down close in every part, or it will be liable to heat too violently.

During the first week to ten days, after the bed is made, the glasses should be but slightly covered in the night, and, in the day-time they should be raised, to let out the steam, which usually rises very copiously, while the dung is fresh: as the heat abates, the covering should be increased.

The hot beds which are made with tanners' bark are preferable to the above, especially for all tender exotic plants or fruits which require an even degree of warmth to be continued for several months. The manner of making these is as follows: -

Dig a trench in the earth, about three feet deep, if the ground be dry: but if wet, not above six inches, at most, and raise it in proportion above ground, so as to admit of the tan being laid three feet thick. The length must be proportioned to the frames intended to cover it, but that should never be less than eleven or twelve feet, and the width not less than six.

This trench should be bricked up round the sides, to the abovementioned height of three feet, and should be filled with fresh tanners' bark, which should be laid in a round heap, for a week or ten days, before it is put into the trench, that the moisture may the better drain out of it.

Then put it in the trench, and gently beat it down, equally with a dung fork; but it must not be trodden, which would prevent it heating, by settling it too close: put on the frame over the bed, covering it with the glasses, and in about a fortnight, it will begin to heat; at which time may be plunged into it, pots of plants or seeds, observing not to tread down the bark in so doing.

These beds will preserve a proper temperature of heat for three or four months, which may be continued two or three months longer by adding fresh bark, whenever the warm begins to decrease.

Frames vary in size according to the plants which they are destined to cover. If designed for ananas or pine apples, the back should be three feet high, the lower part fifteen inches: when the bed is intended for taller plants, the frame must be made proportionally higher; if for seeds only, it will not be necessary to employ frames more than fourteen inches in height at the back, and seven in the front. The glasses of hotbeds may be shifted or tilted at one end, to admit the fresh air, and to let out the steam, as occasion may require.

See also a short history of hot beds.