PEAR GROWING IN CALIFORNIA. 335 



Fig. 140. This picture was taken in a pear orchard in one of the 

 colder locations in El Dorado County. It will be noted that the pots 

 were placed midway between the tree rows in the center of each rec- 

 tangle formed by four trees. Usually in addition a double row of pots is 

 placed just outside of the border rows in order that they may receive 

 ample protection, which is made more difficult because of the open 

 exposure. 



Success in the orchard heating work is dependent upon the care 

 that the various operations receive. In the first place the heaters 

 should be filled and placed in the orchard in plenty of time before the 

 frost period arrives, as the placement and filling of pots at the last 

 minute is not conducive to the best results. The heaters must be 

 lighted before the temperature reaches a point where the fruit will be 

 killed. For example-, if thirty degrees Fahrenheit will kill buds the 

 heaters should be burning when the thermometer has reached thirty- 

 four or thii'ty-two degrees. It is much easier to maintain a certain 

 temperature above freezing than it is to raise the temperature above 

 that point after it has dropped several degrees below. Tested ther- 

 mometers should be used in orchards where heaters are used. They 

 must be watched during the danger period by careful men who can 

 be depended upon not to fall asleep just at the critical time. 



Ligliting of the heaters must be done quickly. This is easily accom- 

 plished by means of a torch brought over the surface of the oil in 

 heater, upon which a little gasoline is squirted from a specially con- 

 structed can. With a little experience men can light the heaters almost 

 without stopping as they pass from one to another. Firing must be 

 continued throughout the entire time that the thermometer registers 

 below the danger point, and also for some little time after it again 

 begins to rise. Sunrise is often a fatal time and it is sometimes neces- 

 sary to keep the heaters burning for some time after the sun has 

 risen. 



