by 



FROST AND THE PREVENTION OF 

 DAMAGE BY IT. 



CONTENTS 



Frost defined 



What is frost? 



How frost is formed 



When to expect frost 



Influence of soil and vegetation 

 on minimum temperature 



Protection from frost 



Conserving heat 



Stirring the air 



Adding heat 



Is orchard heating profitable? 



Maximum cost of firing 



Average cost of firing 



Page. 

 8' 

 3 

 4 

 8 



10 

 11 

 11 

 14 

 14 

 30 

 32 

 32 



Is orchard heating profitable Con. 

 Best methods of handling or- 

 chard heating 



Frost and -minimum temperature 



forecasts 



Injurious temperatures 



Influence of humidity on rate of 



freezing 



Deciduous fruits 



Citrus fruits 



Meteorological instruments and ex- 

 posures 



Measurement of atmospheric 

 moisture 



Page. 



34 



36 

 36 



37 

 38 



42 



46 



FROST DEFINED 



WHAT IS FROST? 



The words "frost" or "hoar frost" are used to designate the 

 deposit of feathery ice crystals which usually form on the ground 

 or other exposed surface whose temperature has fallen to 32 F., the 

 freezing point of water, or lower. In a larger sense, the occurrence 

 of any temperature of 32 F. or lower, whether accompanied by a de- 

 posit of ice crystals or not, is called a frost. 



Frosts are spoken of as light, heavy, or killing, depending on the 

 degree of damage to growing crops. Since the same temperature 

 that kills young tomato plants may not injure fruit blossoms, a 

 frost that would be called " killing " by one person may be regarded 

 as " light " by another. During the growing season a period of 

 extremely cold weather accompanied by strong winds, when the air 

 for a considerable distance above the earth is chilled, is sometimes 

 called a " freeze." True frosts occur only when the surface air is 

 relatively calm. 



In order to understand the underlying principles of frost protec- 

 tion it is necessary to know something of the methods by which the 

 ground surface and lower air cool during the night. 



150830 20 Bull. 1096 2 3 



