FORCING AND FORCING STRUCTURES 77 



The crops are removed as soon as mature ; the soil is spaded 

 up and, by the addition of sterilized manure, fine ground bone 

 and lime may be kept in very satisfactory condition for three or 

 four years. 



Disinfecting the greenhouse. The houses, however, should be 

 thoroughly disinfected during the summer months when they are 

 empty, by burning sulphur and by spraying them thoroughly with 

 a solution of i part of formaldehyde to 50 gallons of water. It is 

 also a good idea to whitewash or paint all of the exposed parts of 

 the woodwork. Fumigation with cyanide of potassium is one of the 

 most effective methods of disinfecting empty greenhouses. 



In many large plants the annual renovation includes sterilizing 

 the soil of the houses by the method described on pages 23-26 or 

 by means of perforated steam pipes buried a few inches beneath 

 the surface. Live steam at a pressure of from 60 to 80 pounds 

 is forced into the perforated pipes for a sufficient period to kill all 

 organic life and germs in the soil. 



Construction of benches for bottom heat. There are many types 

 and methods of constructing greenhouse benches. A satisfactory ar- 

 rangement is to provide carriages made of 2 x 4 inch or 3 x 4 inch 

 dimension stuff, and so arranged that a front board can be placed 

 outside the support next to the walk, in order to provide a smooth 

 wide board next to the walk, as shown in figure 24. This can be 

 accomplished by using 2x4 inch or 3 x 4 inch stuff for legs and 

 ripping it to the depth of the bench so as to leave a portion i inch 

 thick to carry the side boards. Saw out the remaining portion at the 

 proper height above the walk for the bottom of the bench and place 

 the bench carriage on the shoulder of the leg so produced. The 

 bench leg on the other side of the carriage should be constructed in 

 exactly the same manner except that the side board should be placed 

 inside rather than outside the leg, as shown at A, figure 24, the leg 

 itself being placed against the side wall of the greenhouse. By this 

 arrangement an air space i inch wide is secured between the back of 

 the bench and the side wall of the greenhouse. This is of great ad- 

 vantage where an even distribution of heat is required and where a 

 low temperature is maintained in the greenhouse at night. Benches 

 which are arranged tight against the side wall and close to the glass 

 are apt to be much colder at the wall side than they are near the 



