PROTECTION AGAINST FROST 365 



Injury to pear flesh apparently must extend well away from the core to prevent 

 the development of the fruit, though it conceivably may interfere to some extent 

 with the so-called "secondary effect" of pollination. 



Impaired germination of pollen of pear, plum, cherry and peach on 

 exposure for 6 hours to a temperature of — 1.5°C. has been reported. ^^^ 

 Chandler^* found that pollen of the Jonathan apple after exposure to 

 — 3°C. showed a germination of 33 per cent, as compared with 84 per 

 cent, for unfrozen pollen, and pollen of the Cillagos apple frozen for 

 30 minutes at — 8°C. germinated 25 per cent, as compared with 67 per 

 cent, for unfrozen. 



Frost Injury and the Size of the Crop. — Finally it must be considered 

 that the damage from a given frost is a varying quantity. Some peach 

 trees on which 1,000 peaches would be a good crop bear 20,000 or more 

 fruit buds. Obviously, with other conditions favorable, a loss of 80 

 per cent of the buds would not interfere with the production of a full 

 crop and in a commercial sense this frost would not prove damaging. 

 If, however, the same trees were bearing only 8,000 buds a loss of 80 per 

 cent might become a serious matter. 



It should be apparent that no set rules of procedure as governed by 

 observed temperatures can be given. Probably the safest course for the 

 grower when freezing occurs is to try to keep the temperature above 

 29°F. if he is heating his orchard and after a frost it is best to proceed on 

 the assumption of a full crop unless the evidence to the contrary is 

 convincing. 



AVOIDING FROST THROUGH LATE BLOSSOMING VARIETIES 



The relatively wide range in blossoming dates of the many kinds and 

 varieties of fruits is often important in determining the relative danger 

 from frost to an orchard on a given site. Conversely, the blossoming 

 dates should have bearing on the decision as to the type of fruit to be 

 planted. On a very large scale the limiting factor in the growth of 

 apricots and almonds is not their lack of hardiness to winter cold, since 

 some varieties are probably as hardy as, or even hardier than, the peach, 

 but rather their extremely early blooming. 



Blossoming Range Varies with Earliness. — The earlier the average 

 date of blossoming in any section the longer is the spread of the ordinary 

 season of bloom. In the north the time between the first peach and the 

 last apple to blossom is frequently shorter than the interval in the south 

 between the first and the last peach. Consequently the relative earliness 

 or lateness in blossoming of a variety may be more important in some 

 regions than in others. Table 69 shows the difference between peaches 

 and apples in the number of times heating might be necessary at various 

 places in Utah. The difference between a total of 263 heatings for the 



