WEATHER IN CRANBERRY CULTURE 49 



rapid growth before a frost, sap concentration will be low and frost nun- injure 

 more and at a somewhat higher temperature than it otherwise would. If low 

 temperatures, unfavorable for growth, ha\'e prevailed for some time, plants will 

 stand more cold. This rule of plant frost tolerance should apply to the cranberry 

 plant more in the spring frost season than in the fall because of the very new 

 growth; but low temperatures in August tend to hasten the ripening of the 

 berries, thus concentrating their juice and giving them greater frost endurance 

 early in the picking season than they would otherwise have.^^ 



4. The material in tables 1 to 6 seems to indicate that the conductivity of the 

 soil has more influence than its temperature on frost occurrence in the spring but 

 is the less important in the fall. Evidently ready availability of heat rather than 

 a large reserve is necessary in the short nights of spring. Slower conduction 

 suffices in the fall because it has more time to function, but the longer nights 

 call for a greater supply of soil heat on which to draw. Conditions in the deeper 

 soil must therefore enter into this more in the fall than in the spring. 



Dew 



Cold nights are generally less dangerous when the dew point is high than when 

 it is low, the temperature not falling so fast or so far because of the liberation 

 of latentTieat by the condensation of water vapor in the air and the considerable 

 return radiation to the ground. Nights with heavy dews are also generally calm 

 (see discussion of wand, above). The heat of fusion coming from a heavy dew 

 when frost forms is also some protection. Heavy dews therefore deserve some 

 consideration in nights with prospective minimum temperatures at the danger 

 line. They help till frost becomes rather general; but the wetter plants are when 

 they really freeze, the more they are likel\' to be hurt.^^ 



Ground Fog 



The fog or mist common "over cranberry bogs on frosty nights returns radiation 

 to the ground and so has a protective influence, ^i but, as Cox indicated, this is 

 slight.«2 



Bog Resistance 



Spring growth starts more slowly on dry bogs than on bogs flowed during the 

 winter. Partly on this account, but apparently also because of resistance gained 

 by winter exposure, such bogs are hurt by frost rather less easily than others. 

 Only early varieties should be grown on dry bogs so that the fruit may be gathered 

 usually in time to escape fall frosts. 



Vine Growth 



A thick and deep vine growth, especially on dry bogs, much increases the frost 

 hazard, for the following reasons: 



1. The more vines the less the soil they cover is warmed by the sun and the 

 more the heat transfer from the soil to the radiating vine surface is restricted at 

 night. 



5^The time of cranberry ripening also depends greatly on weather conditions in the spring (p. 89). 

 ^"Smith, J. Warren, Agricultural Meteorology, 1920, p. 140; Schoonover, Brooks, and Walker, 

 op. cit., p. 14. 



^^Young, op. cit., p. 8; Allen, op. cit., pp. 288-289. 

 62Cox, op. cit.. pp. 88-89. 



