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Hotbeds. Low glass structures in which plants arc started or grown, usually heated by fermenting vegetable substances, such as stable-manure, although fire heat is occasionally applied, steam, hot water and flues being used. Their usual place is some spot sloping to the south, where they are protected by buildings, evergreen screens or board fences, from the north and west winds (Fig. 1911). The frames are made either of plank or boards and may be portable, or built in place, the former being taken down and packed away except when needed. A tight board fence 6 feet high, as a windbreak, is desirable, as it will also serve as a support for the shutters, mats and sash when they are removed from the bed, and it will answer best for this purpose if it inclines a foot or so to the north.

When movable frames are used, they are generally constructed of 2-inch plank, the side pieces being from 9 to 12 feet and the ends 6 feet in length, to receive either three or four ordinary sash, which are 3 by 6 feet. The north side of the frame is made 15 inches wide, while the south side is but 9 or 10 inches, thus giving a slope to the south, which will permit the water to run off and favor the passage of the sun's rays through the glass. The end pieces are 6 feet in length, and in width taper from 15 inches at one end to 9 or 10 at the other, so as to fit the side boards. The plank for portable hotbed frames may be held in place by means of stakes, or iron rods or bolts may be fastened to the ends of the side pieces so that they can pass through the holes in the ends of the frame, which can then be secured by keys or nuts. As supports for the sash and to hold the sides of the frame in place, cross-strips of board 3 inches wide are sunk into the upper edge every 3 feet, and another strip with a width equal to the thickness of the sash is fastened on edge to the center of its side. Frames of this size require a slightly deeper mass of heating material than would be necessary for larger frames, and when they are to be used during the winter, it is well to excavate to the depth of 2 ½ feet and for a space 2 feet longer and wider than the frame, and after the hole has been filled with heating material, the material should be well tramped down. The frame is then put in place and manure is banked about it.

For permanent frames, rough 1-inch boards may be used, although 2-inch plank will be found far more durable. Stout stakes should be driven into the ground about 4 feet apart, where the north line of the bed is to be located. These should project above the surface from 12 to 15 inches, and should be boarded up from a point just below the level of the ground, so that the stakes will be on the north side of the frame. A second row of stakes should then be driven at a distance from the first row equal to the length of the sash, which is usually 6 feet, although other lengths are sometimes used. The south wall of the frame should then be boarded up so that it will be 5 or 6 inches lower than the north wall, after which the end should be closed and cross-pieces should be fitted, the same as for the portable sash. To prevent frost from working into the frame, soil should be taken from the inside and banked against the boards outside, so that it will reach two- thirds of the way to the top of the frame, and when the bed is ready for use, 3 or 4 inches of horse-manure should be spread over this. The frame should be placed about 3 feet from the fence, and if other rows are needed, there should be alleys about 7 feet wide between them.

Instead of boards or planks, concrete may be used for the walls of permanent frames. Forms should be set so that the lower part of the wall will be 4 inches thick but it may be only 2 ½ or 3 inches on the top. The excavation for the wall should extend about 1 foot below the surface and to prevent the settling of the concrete walls, when the excavation for the bed itself 

is made, concrete piers about 6 inches square should be built every 6 feet for the wall to rest upon. They should extend nearly 2 feet below the wall. The walls of the excavation will serve as a form for the piers and if care is taken in making the excavation for the wall itself, there will be no need of making a form for the outside of the walls below the surface, but plank should be set up for the inside of the walls, and for both sides of the wall above the surface. For making the grout, use four parts of gravel, two parts of sharp sand and one part of cement. Mix the sand and gravel and then after adding and thoroughly mixing the cement, pour on water enough to make a "wet mix." Pour the grout into the form, thoroughly packing it, and then allow the form to remain until it has set.

Hotbed sash.

The size that has been found most satisfactory for hotbed sash is 3 by 6 feet, as when larger than this they are not readily handled by one man. While pine and other native lumber may be used, cypress is generally preferred, as it is much more durable and costs but little if any more than clear pine. The sides and upper ends of the sash are made from 3 by 1 ½ -inch strips, grooved to receive the glass, while the lower end is about 1 by 5 inches. The center strips are 1 by 1 ½ inches. For glazing hotbed sash, single-strength 10 by 12 glass is commonly used, as three rows of this size will fill a sash 3 feet wide. While double-strength glass will be less easily broken, the increased weight is an objection to its use. The use of double-glazed sash is often advised, but aside from the extra cost, it will be found that the sash will be heavy to handle and, if used near where soft coal is burned, the bottom rows of glass will soon become nearly opaque and it will be necessary to re- glaze the sash in order to wash the glass. Where there will be no trouble from soot and the sash is to be used for the covering of half-hardy plants in the winter, double-glazed sash may be used with satisfaction. The sash should receive two coats of paint, and after the glass, which may be either lapped or butted, has been set, it should be given a third coat.

Mats and shutters.

For covering the frames on cold nights during the winter and early spring months, straw mats are often used, although those made of burlap are generally preferred. The burlap may be either single or doubled, or it may be stuffed with straw, excelsior or other materials. Quilted mats filled with combination wool are very warm and quite durable. During the winter, wooden shutters are also desirable to place over the mats, as they assist in holding the heat, and by keeping the mats dry, aid in preserving them.

Heating material for hotbeds.

To provide heat for the beds decomposing horse- manure is generally used. While a large amount of straw is not desirable, the presence of urine-soaked bedding with the manure to the extent of one-third its bulk is not objectionable, as it will lengthen the heating period of the manure. Unless straw is mixed with the manure, it will be well to add forest leaves to the amount of one-third to one-half the amount of the manure. The heating material should be forked over and placed in a pile 5 to 6 feet wide, 3 to 4 feet high and of any desired length. If the manure and straw are dry, it will be well to moisten them with a fine spray. In case there is but a small amount of manure, it will be best to use warm water, though in all cases the soaking of the manure should be avoided. Within four or five days the giving off of steam will indicate that heating has commenced. The pile should then be forked over, working the outer portions into the center.

The amount of heating material that will be required for a hotbed will vary with the crop, as well as with the location and season. For zero weather, there should be at least 18 inches of heating material after it has been well packed down, and 24 inches will be desirable in midwinter in the northern states, while 6 to 8 inches may answer where only a few degrees of frost are expected. For 18 inches of manure, the excavation should be made to a depth of 28 inches below the level of the south side of the frame, and 31 inches below that of the north side. After the manure has warmed through for the second time it should be placed in the excavation, spreading it evenly and packing it down with the fork, but leaving it for a few days before tramping it. Care should be taken to have the corners well filled, that an even settling may be secured. After the manure has again warmed up, it should be thoroughly tramped.

The bad is then ready for the soil, which should be quite rich and contain a large amount of sand and humus, a compost of decomposed pasture sods with one- third their bulk of rotten manure being excellent for the purpose. The thickness of the soil should vary from 5 to 7 inches, the greater depth being desirable for radishes and other root crops (Fig. 1913). When boxes of plants are to be placed in the beds, the depth of soil need not be more than 3 inches. For a few days the bed will be quite warm, but when the temperature of the soil has dropped below 90° the seeds may be sown or the plants set out.

In severe weather the mats and shutters should be placed on the bed at night and should be removed in the morning. When the sun is shining, or if the bed is very hot, it should be ventilated by raising (Fig. 1914) or slipping down (Fig. 1912) the sash, the amount depending upon the season and the condition of the bed. By the middle of the afternoon the sash should be closed and the covering should be replaced before night. When used in the winter time, the hotbed should be either sunk in the ground or well banked up with soil or manure, so as to keep out the frost.

Fire-heated hotbeds.

Especially if the beds are to be used during the winter months, and where there is an abundance of wood for fuel, it is advisable to use artificial heat for hotbeds. The simplest and cheapest method of heating is by means of hot-air flues. These do not differ materially from greenhouse flues except that they run underground and 6-inch sewer-pipe is used for them. The best results are obtained when the beds are built on the slope of a hillside, as this improves the draft. A 
small furnace or firebox is constructed of brick or concrete at the lower end of the frames from which one or more lines of hotbeds may be heated. As a rule, it is not best to heat more than two rows of frames from a furnace.

The flues are placed so that they will be 10 or 12 inches below the surface of the soil in the frames and they should rise gradually toward the farther end, where they should be connected with a pipe which will serve as a chimney. The height should vary from 6 to 10 feet, according to the length of the frames. For use in the winter, there should be two flues in a frame 12 feet wide.

When the hotbeds are located near a greenhouse heated by steam or hot water, it will be found satisfactory, particularly if the beds are higher than the heating plant, to put in either hot-water or steam pipes for heating them. While beds 6 feet in width may be heated in this way it is better to make them about 12 feet wide, with a ridge in the center and a row of hotbed sash on each side. To heat such a frame with hot water, a 2 ½ -inch flow-pipe should be run just under the ridge and there should be one or two 2-inch returns on each of the side walls. For use in the spring, one return on a side would answer, but in the winter months two will be necessary in sections where the mercury reaches zero, unless the beds are covered to prevent the escape of the heat. When steam is used, the feed pipe should be 1 ½ or 2-inch and 1 ¼ -inch pipe should be used for the returns.

In the northern states, it is seldom desirable to use hotbeds of any kind for the growing of winter crops, as not only can better results be secured in greenhouses, for which the cost will be but little more, but the work of handling the hotbeds in cold, stormy weather will be very disagreeable and unsatisfactory. In the South, however, hotbeds answer very well for winter use, both for growing plants for the truck-garden and for the forcing of various vegetable crops, although even there the simply constructed greenhouses would be more satisfactory.

Coldframes.

As an adjunct to the greenhouse when one is growing truck-crops, or bedding-plants, a coldframe will be found very helpful. These differ from hotbeds only in relying upon the sun for their heat. The surface of the soil should be from 6 to 12 inches below the glass.

If plants are to be grown in the soil of a frame, care should be taken that it is adapted to the crop and that it is well stored with available plant-food. In many cases the frames are merely used for the hardening of plants which have been grown in the greenhouse, or for the carrying of half-hardy plants through the winter. For these purposes the soil m the frames should be of a sandy or porous nature.

Glass sash should be used for covering the frames in the winter but, in the spring, canvas and other substitutes answer very well, particularly when the frames are to be used for the growing of seedlings. A long strip of canvas may be stretched lengthwise of the bed as a covering at night and upon cold days, and removed in whole or in part in pleasant weather. Oiled paper and water-proofed muslin are also used as substitutes for glass in hotbed sash.

Management of hotbeds.

If the weather is mild during the latter part of February, the manure can be procured and prepared for use so that the hotbed may be started about the first of March. If properly constructed they will provide heat for two months, and can then be used during May as coldframes, thus making it possible to take on two crops in the spring. Although it is not often practised, they may be used in the fall for growing a crop of lettuce or other vegetables, which can be matured before the first of December.

If a greenhouse is not available for starting the plants, seeds of lettuce, radishes, cabbages and other of the hardier plants may be sown in the hotbed in the spring as soon as it is ready, in rows 4 or 5 inches apart. When the first true leaf appears, the radishes should be thinned and the other plants transplanted to about 2 inches. Later on, the lettuce plants should be placed about 8 inches apart each way. If the weather is so cold that the bed should not be kept open, the seeds may be sown and the first transplanting may be in flats or boxes, which can then be placed in the beds. Aside from proper ventilation, covering and watering, the beds should occasionally be weeded and the soil stirred. About the first of April, tomatoes, cucumbers and similar plants may be started. As soon as one crop is taken off another should be placed in the beds, and by deepening the soil they may be used during the early summer for growing cauliflower, tomatoes and cucumbers. 
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