442 VEGETABLE GARDENING 



Ordinary hotbeds are often used in propagating the 

 plants. The amount of manure required depends upon 

 the locality. A depth of I foot of fresh manure is usually 

 sufficient. The soil is not added until the bed has begun 

 to heat. 



In some sections through the northern area of the 

 sweet potato district flue-heated beds are employed. 

 These are very common in New Jersey. Figure 101 

 shows such a structure with the canvas covering re- 

 moved. The canvas is kept over the beds during the 

 early stages of rooting and removed later when weather 

 conditions permit, but replaced in cold or frosty weather. 

 The flues may be built of wood, tile, concrete or brick. 

 The walls of the bed are of any desired construction, 

 and frequently sash are used for covering instead of 

 canvas. 



Pipe-heated beds are popular in some sections. Beat- 

 tie (U. S. D. A. Farmers' Bui. 324, p. 12) gives the fol- 

 lowing description of this method: "Where a steam or 

 hot water boiler is in use for greenhouse or residence 

 heating, a very satisfactory plant bed can be constructed 

 by burying four or five lines of pipes in the soil beneath 

 the bed and supplying the heat from the boiler. This 

 has been found to be an ideal method, as the lines of 

 pipes can be controlled by valves and the temperature 

 of the soil in the bed kept at the desired point. If hot 

 water heat is used the pipes should be laid with the soil 

 in direct contact with them, but for steam the pipes 

 should be surrounded with 3-inch or 4-inch tiles to pre- 

 vent too rapid passage of the heat and the consequent 

 burning of the soil. The pipes should be placed 10 or 12 

 inches below the bottom of the special soil in the bed, 

 and 14 to 16 inches below the line of the seed potatoes. 

 If the pipes are laid 18 inches apart, an even distribution 

 of heat will be secured. For hot water heating, 2-inch 

 pipes should be employed, but i^4-inch pipes will be 



