EFFECTS OF FREEZES ON CITRUS IN CALIFORNIA 277 



off to depreciation has varied according to the equipment and the 

 usage that it received. The depreciation on the oil heaters has usually 

 been as high as 25 per cent and that on the other equipment probably 

 about 10 per cent. 



The cost in the groves where the best work was done ranged from 

 5 l / 2 to 6 l /2 cents per gallon of oil consumed; or, figured on the acre 

 basis, from $50 to $100 an acre was spent in these groves. With 

 increased experience and improved equipment, it ought to be possible 

 in the future to lower these costs. At present the items of labor and 

 of depreciation contribute too large a percentage to the total cost. 

 The equipment of the future will probably last longer and require 

 less attention during its operation.* 



FACTORS INFLUENCING RESISTANCE OF TREES TO COLD INJURY 



It has already been noted that there was a marked difference in 

 the resistance that different citrus trees showed toward the cold 

 weather. Trees side by side were often very differently affected. 

 It was evident that these differences were not always due to differences 

 in temperature, and a search was made to discover why certain trees 

 should have withstood the cold so much better than others. 



Dormancy of Trees. Trees that were dormant and inactive were 

 able to stand much more than those which were growing and where 

 the parts of the plant were actively functioning. Orchardists recog- 

 nize this fact by their expression that trees in a "sappy" condition 

 are more easily damaged than trees which are more "mature." 



The treatments that stimulate a tree to growth or to activity, there- 

 fore, should be omitted, if possible, when cold weather is to be expected. 

 This applies particularly to young trees. Some growers feel that with 

 lemons, at least, it is more profitable to keep the trees growing through 

 the cold weather and protect them from damage by heating. 



Some of the things which influence the dormancy of citrus trees, 

 as recorded by the freeze, are dryness and the time of irrigation, 

 pruning, and, in young trees, the time of planting. 



Time of Planting. Young trees which were planted so late in the 

 fall that they had not started to grow at the time of the freeze were 

 much hardier than trees similarly located that had been planted in 

 the summer or in the spring and were growing. In one young grove, 

 that was set in the spring of 1912, most of the growing trees were 



* The California Cultivator, Los Angeles, June 26, 1913, gives some excellent 

 articles on the protection of citrus groves against cold. 



The Pacific Rural Press, San Francisco, May 24, 1913, has an excellent state- 

 ment on cost of heating. 



The Monthly Bulletin, State Commission of Horticulture, vol. 3, no. 1, has an 

 article giving costs of heating a large acreage. 



:ITRICULTTJ:RE 



