The roots should be bedded in the hotbed a month or six weeks previous to planting time. In the latitude of Washington, where planting begins May 10, the roots should be planted in the hotbed about April 1 to 10. Usually in the first two weeks in April there is a warm-wave which hurries out the peach blossoms, and these are followed a week later by the pears. The bedding season, therefore, may be considered as the time when peaches and pears are in blossom. In the northern states it is necessary to bed the potatoes in hotbeds a month or more earlier than the climate will permit them to live in the field.
Various types of hotbeds are in use. The sim plest arrangement for the southern states is a little pit or frame sunk in the ground ; about six inches or more of manure is carefully filled in; and a four to-five-inch layer of good sandy loam is placed on the manure. This should be moistened, after lying about forty-eight hours for the first heat to pass off, es pecially if the manure is new; the potatoes can then be bedded. Bedding or planting sweet-potato "seed-roots" consists simply in laying them on the soft sandy soil, preferably with their ends all in one direction, and cross-ways of the bed ; when the potatoes are curved, the convex side should be upward, thrusting the points in the sand. They are then covered with the same sandy loam to a depth of about one and one-half inches above the upper surface of the roots. Some growers prefer to cover them lightly, say one-half inch ; then, after the tips appear, to add the additional inch of soil. The simplest protection consists of a layer of pine leaves six inches thick. This has to be carefully watched, however, and removed as soon as the sprouts begin to appear, otherwise slender white "drawn" sprouts will result. A better covering is a cheap grade of white cotton cloth, and a still better one is the ordinary hotbed sash. Extensive beds, utilizing several dozen sashes, are in use by some growers.
Wherever glass sash is used, careful attention has to be given on the first warm days, especially after the sprouts appear, to ventilate the beds by placing a block under the end of one sash and under the opposite end of the next sash, and so on.
Before the plants are up a warm spell may be had, or, through some unusual activity of the fer menting manure, sufficient heat may be generated to cause the roots to decay. Old-time gardeners trust to their sense of feeling in changing the heat.
A better method is to use a thermometer and to keep the temperature as low as 90° Fahr., preferably between 80° and 90°.
The best method of propagating the sweet-potato in the North is through the fire hotbed (Fig. 840). The intense bottom heat, with the exposure of the plants to the open air during a large part of their growth, not only makes this an effective method of getting large quantities of plants, but with proper attention to the covering and watering the plants will be of the most desirable quality. Briefly, the fire hotbed consists of a floor or bed on floor beams or joists with a two-foot air space underneath and with a brick furnace at one end, from which tile flues carry the heat part way across the bed. At the opposite end a wooden flue, some ten feet in length, carries off the smoke and furnishes a draft. The bed should be sunk in the ground nearly to the level of the soil and should have a tilt or in cline of about one foot to every twenty or thirty feet of length. Since the upper half of the bed, or rather the air space beneath it, serves as a chimney, this inclination is required to carry the smoke and hot air from the furnace to the far end of the bed. With this inclination the bed will be but little warmer over the furnace than it is at the opposite end. The brick arch or furnace should be depressed so that its top is three feet below the floor beams. It is then covered with a foot of soil, making the two-foot air space continuous. In an average sized bed, say sixty to eighty feet long and twelve to fourteen feet in width, the furnace should be six feet by two feet six inches inside, so as to burn cord-wood. The flues should be of six-inch tile and should extend for about thirty feet, gradually rising to the surface of the ground until at the outlet it is raised one inch above the ground. At thirty feet from the furnace the smoke and the fumes will be sufficiently cooled to permit dis charging into the air space without danger. An inch or two more of soil, however, should be placed under the plants in that part of the bed directly over the furnace and over the discharge of the tile flues. No wood construction can be used in touch with the furnace. The end wall has to be built of brick or stone. To avoid digging a pit in which rain may collect, it is best to place the bed just at the crest of the hill, allowing the furnace end to extend over the crest.