FREEZING OF FRUIT BUDS 



By Frank L. West, Physicist, and N. E. Edlefsen, 1 Assistant Physicist, Utah Agri- 

 cultural Experiment Station 



INTRODUCTION 



Killing frosts occur in the late spring and early fall over large areas of 

 the United States, causing damage to the extent of several millions of 

 dollars annually. The commonest method of protection is to heat the 

 area by burning oil in pots distributed through the section that is endan- 

 gered. Heating is resorted to on a large scale in the citrus fruit sections 

 of California and less frequently elsewhere for the protection of such 

 fruits as apples, peaches, and cherries. The success of this practice de- 

 pends on the economical use of fuel and labor. If the predicted mini- 

 mum temperature is lower than the "critical temperature" by an amount 

 that exceeds the rise in temperature that the heaters will produce, or if 

 the minimum temperature is above the "critical temperature," then the 

 heaters should not be lighted. In order, therefore, to be able to tell 

 when to light the heaters, it should be known how hardy the buds are. 

 This paper gives the methods used and the results obtained from freezing 

 more than 24,000 fruit buds, most of them being apples and peaches, 

 and also the spring freezing temperatures and the yields of fruit in 

 orchards near Logan, Utah, from 191 3 to 1920. 



THEORY OF INJURY DUE TO FREEZING 



Pure water freezes at 32 ° F. Salts dissolved in water cause it to 

 freeze at a lower temperature than this, the amount of the depression of 

 the freezing point depending upon the nature of the salt dissolved and 

 also upon the concentration of the solution. Thus, a 5 per cent common 

 salt solution freezes at 27 , while a 30 per cent sugar solution freezes at 

 only 29 F. W. H. Chandler 2 found that the expressed sap from fruit 

 buds froze at 2 8° to 29 and in no case required a temperature below 2 8°. 

 The sap from Elberta peach twigs, extracted in March, froze at 28. 7 , 

 while but two-thirds of the twigs of the same kind of fruit when subjected 

 in March to a temperature as low as io° froze. It is frequently found 

 that some of the buds withstand temperatures as low as 20 and mature. 



The more concentrated the aqueous solution, the lower is its freezing 

 point, and in 'general the amount of the substance, especially if it is 

 organic, that will dissolve in water is but slightly affected by the sub- 

 stances that are already in solution. This allows the possibility of a 



'Messrs. J. Z. Richardson, W. E. Goodspeed, and Scott Ewing rendered valuable assistance with the 

 laboratory and field work. 



! Chandler, W. H. the killing of plant, tissue by low temperature. Mo. Agr. Exp. Sta. Re- 

 search Bui. 8, 309 p., 3 pi.: chart. 1913. Bibliography, p. 305-309. 



Journal of Agricultural Research, Vol. XX, No. 8 



Washington, D. C. Jan. 15, 1921 



wp Key No. Utah-12 



(655) 



