270 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION 



which it furnishes, causing a more gradual warming of the plants 

 after the frost. At night the lath probably reflects back some of the 

 heat radiated from the ground, and it also shuts in a pocket of warm 

 air. 



PKOTECTION BY AETIFICIAL HEATING 



The cold weather of January, 1913, demonstrated to the citrus 

 growers of Southern California that the only successful way thus 

 far devised for fighting cold weather is the use of orchard heaters. 

 To be sure, success was not universal with those who tried to heat 

 their groves, but there were enough successes to show that where the 

 equipment and supplies are adequate and the work well done orchard 

 heating is effective. 



So much doubt has existed in the minds of many growers as to 

 whether artificial heating is effective and pays that special observations 

 on selected plots of heated and unheated areas were made by several 

 investigators. A report on some of these observations will be given 

 as a separate article in another part of this bulletin. General state- 

 ments only will be given here. 



Acreage and General Results. In all there were several thousand 

 acres in California that had been equipped with orchard heaters for 

 the winter of 1912-13. In a part of this acreage the equipment was 

 entirely inadequate and allowed only a weak and ineffective effort to 

 be made when the cold weather came. In general, however, those 

 who tried to heat their groves obtained results which satisfied them 

 that it had paid. There were many heated groves where the entire 

 crop was saved and where the trees showed no effects of the cold, 

 while neighboring groves which were unheated lost their crop of fruit 

 and suffered such tree damage that it was two years or more before 

 they began to pay expenses. In some lemon groves where successful 

 heating was done the fruit from the first pick, which was made after 

 the freeze, brought enough to pay the entire cost of heating, including 

 the cost of the equipment, and then paid the grower a good profit 

 besides. In addition to saving the fruit which brought in these returns, 

 the young fruit and bloom of these trees was not frozen and there 

 was no injury to the fruiting wood. Results were not always so 

 satisfactory as this, but failure could always be traced to improper 

 equipment, a shortage of fuel, or a lack of vigilance. Failures were 

 seldom complete, however, and the condition of the trees usually 

 showed benefit from the heating, even when the crop was lost. 



Equipment and Material. Most of the heating was done with pots 

 burning oil, many kinds of which were in use in different groves. In 



