Frost-Protection 251 



PBOTECTING PLANTATIONS FROM FBOST 



Having considered (in Chapter II) the relations of 

 location, site and windbreaks to cold and frost, we may 

 address ourselves to a discussion of the means by which 

 injury from local frosts may be averted, in case they 

 threaten to occur. These means are of two types, — ^those 

 that attempt to enable the plant to escape injury from the 

 frosts, and those that attempt to prevent the frost from 

 occurring. Altogether several general means have been 

 proposed for protecting plants from frost, and there are 

 also combinations of the methods. The methods are 

 mulching, covering the plants, whitewashing the plants, 

 adding the vapor of water to the atmosphere, explosives, 

 causing currents of air, making artificial clouds, and heat- 

 ing the air. 



The temperatures at which the fruit-crop may be 

 injured by frost are discussed to some extent in Chapter 

 VIII (page 313); but O'Gara summarizes the advice as 

 follows : "The temperatures at which the principal orchard 

 fruits are liable to be injured cannot be accurately stated, 

 since weather conditions previous to a freeze determine 

 to a very great extent the ability of plants to withstand 

 low temperatures. Not only do the different degrees of 

 cold produce different effects on the same plant, but the 

 same plant will often behave differently when subjected 

 to the same degree of cold. It is well known that plants 

 or parts of plants in active growth are more easily killed 

 by low temperatures than the same plants or parts of 

 plants when dormant. Actively growing plants contain 

 large quantities of water; that is to say, the protoplasm 

 or cell-sap is watery, and, as a rule, the larger the pro- 

 portion of water contained within the plants the more 



