62 The Fruit-Growers Guide-Book 



about 20 degrees would be the point of danger. When the 

 petals are beginning to fall, 28 degrees above zero is cold 

 enough to cause uneasiness. When the petals are off they 

 can stand 30 degrees above zero. When the "shucks" 

 (calyx tubes) are beginning to fall off, 32 degrees above 

 zero is the danger point. 



The United States Department of Agriculture makes 

 the statement that the danger point for apples when they 

 are showing pink is 20 degrees. above zero; in full bloom, 

 26 degrees above; pears showing pink, 20 above zero; in 

 full bloom, 27 above zero; peaches showing pink, 23 above 

 zero; in full bloom, 28 above zero. 



Professor P. J. O'Gara stated that in southern Oregon 

 the temperature at which apricot is injured when in the 

 bud is 28 degrees above zero and at 30 degrees when in 

 blossom; cherries are injured at 29 degrees just before 

 the blooms open, and plums injured at 30 degrees above 

 zero when the flowers begin to show white. 



These figures are not absolute, and will vary slightly 

 from year to year and with the conditions of the bud, but 

 they will serve to indicate that the buds will not be in- 

 jured when the temperature falls below the freezing point 

 for a couple of degrees. Bearing this in mind it will be 

 apparent to the orchardist that it will not be necessary to 

 start up the heaters until the temperature has reached the 

 freezing point, and if the prospects are for only a few 

 degrees of frost it will not be necessary to light up all of 

 the fires in the orchard, but to hold some of them in re- 

 serve. 



In heating the orchard it is not necessary to run the 

 temperature more than to the freezing point, or at most 

 a couple of degrees above, as there is nothing gained. In 

 fact it may be even objectionable through causing the 

 buds to grow a little and become even more tender than 

 they would be if the temperature is held close to the frost 

 line. To be certain as to the departure of the temperature 

 above or below the freezing point it is necessary that the 

 orchard be provided with several thermometers located at 



