CHAPTER XIX 



THE OCCURRENCE OF FROST 



Though spring and autumn frosts determine the geographic Hmits 

 of certain fruits less frequently than minimum winter temperatures, 

 they are nevertheless of no small importance in fruit production. There 

 are some whole sections of the country, as for instance the high table 

 lands of eastern Oregon, where fruit growing is very uncertain because 

 frost may occur at almost any time during the growing season. There 

 are many other sections or areas where spring frosts frequently occur 

 so late that certain fruits such as the apricot or the almond cannot be 

 successfully, or where autumn frosts are so early that late maturing 

 fruits such as the grape do not ripen properly and consequently are not 

 grown. Furthermore, within regions or sections that are suitable for 

 fruit culture there are many sites or locations which, because of their 

 susceptibility to frost, are unsuited for orchard purposes or where, if 

 fruit is planted, it requires expensive artificial protection from frost. 

 Finally, there come years when untimely frosts levy a heavy toll on 

 the fruit crop in isolated places or over wide areas generally considered 

 to be favorably located for fruit production. Early autumnal frosts 

 seldom cause concern so far as the season's crop is concerned, though in 

 grapes and some of the late maturing or everbearing types of small 

 fruits they may be responsible for considerable damage. On the other 

 hand, comparatively few and exceptionally fortunate are the fruit growers 

 who are entirely free, year after year, from concern about possible spring 

 frosts. The cost of full protection from spring frosts of certain pear 

 orchards in the Rogue River valley has amounted sometimes to $40 

 per acre. It is quite likely, however, that many crop failures arising from 

 other causes are attributed to frost damage and it is certain that much 

 can be done to lessen this injury by the careful selection of kinds and 

 varieties of fruit adapted to the particular situation or by selecting 

 a situation suitable to the kinds or varieties of fruit that it is desired to 

 grow. Furthermore, under favorable circumstances much can be accom- 

 plished by palliative methods, such as heating the orchard. 



FROST FORMATION 



Though discussion of the nature, occurrence and prediction of frosts 



belongs properly in treatises on meteorology, a brief outline of the 



more important facts concerning frost formation, so far as they concern 



the fruit grower, seems necessary here because this subject is not studied 



22 337 



