38 Diseases of Greenhouse Crops 



a depth of one foot to insure an open, porous con- 

 dition. The water is heated in an ordinary boiler 

 such as is used for heating the greenhouse, no extra 

 equipment being needed. It is moved by a small 

 pump operated by a motor and gasoline engine of 

 a small horse power. The water comes out under 

 forty pounds pressure, which insures considerable 

 penetration into the soil. It is piped from the boiler 

 through the center of the greenhouse in i^-inch 

 iron pipes. Most growers take the water from the 

 bottom of the boiler rather than from the top, the 

 object being to keep the temperature high but to 

 avoid the steam which is objectionable. A ther- 

 mometer is screwed into the main outlet pipe and 

 is read frequently; the temperature should be above 

 201 degrees F., but if it goes much above 215 de- 

 grees F. the outlet pipe spits steam and is difficult 

 and dangerous to use. To this iron pipe in the cen- 

 ter of the house is attached a one-inch rubber hose 

 fifty feet in length. This hose is replaced annually 

 to decrease the danger of blow-outs and burns. 

 Most growers sterilize once a year, some twice. The 

 rubber hose is attached at the other end to a Y 

 joint which is in the middle of a five-foot iron pipe 

 one inch in diameter. The upper half of this pipe 

 is plugged at both ends, serving simply as a handle, 

 and from the lower half the water is delivered to 

 the soil. A few feet back of this exhaust pipe the 

 rubber hose is wrapped with burlap so that it may 

 be carried over the shoulder of the workman. Some 



