36 MASS. EXPERIMENT STATION BULLETIN 402 



The latest spring frost generally harmful to Cape Cod bogs came the night of 

 June 20-21, 1918, when the temperature fell to 26%° F. at the experiment sta- 

 tion bog and to 23° on some bogs. It reduced the cranberry crop prospect over 

 half (estimated) and so hurt the vines on some areas that their 1919 crop was also 

 curtailed, all new growth being killed. 



Frosts causing slight or local injury on Massachusetts bogs have occurred as 

 late as July 3 and 4 (1927 and 1929). 



Fall Frosts 



Bogs in cold locations sometimes suffer from frost late in August. The earliest 

 late-summer frost recorded as occurring on Cape Cod bogs came August 16, 1912, 

 when the bog temperature at the observing station at South Carver fell to 28° F. 

 The next earliest frost on record came August 22-23, 1923, the lowest bog tem- 

 perature observed being 27° at Norton. Bog temperatures ranged down to 25° 

 on August 24-25, 1940, and it was estimated that frost took 5,000 barrels of 

 cranberries. 



The earliest fall frosts to cause severe and general cranberry loss on the Cape 

 occurred the nights of September 10-11 and 11-12, 1917. Bog temperatures 

 ranged down to 22° F. at cranberry observing stations and to 18° in other places. 

 Because of a backward spring and early summer, cranberries were very late in 

 ripening and were still green or only partly colored when these frosts came. The 

 estimated cranberry loss was 60 per cent in Massachusetts and 25 per cent in 

 New Jersey. 



Cranberries in the whitish state that precedes reddening usually endure a 

 temperature of 28° F. without hurt, but 26° often harms such fruit greatly. 



Some softening among ripe Earl)' Black or Howes cranberries usually' follows 

 exposure to 22° F., but none results from 23°. Ripe Howes are so resistant that 

 under bog conditions often only 10 per cent are softened by 16°, only 20 per cent 

 by 14°, and only 55 per cent by 9°; but sometimes 25 per cent are softened by 18°. 

 With Early Black and Centennial berries the loss at these temperatures is always 

 much greater. 1^ Ripe McFarlin, Bugle, and Smalley Howes berries endure frost 

 as well as Howes. 



Unripe, even wholly whitish, cranberries down among thick vines are hurt by 

 frost much less than well-colored ones in the tops of the same vines, the reduction 

 of radiation of heat from the under-berries by the vines and top berries over them 

 and their greater exposure to conduction, convection, and radiation from below 

 more than balancing* the difference in resistance due to unequal ripeness. For 

 this reason, crops of cranberries well hidden among the vines escape injury from 

 more severe frosts than crops jnore exposed.'* Berries of thin vines, lying on or 

 very close to the sand, are protected by heat conducted directly from the soil and 

 are not easily injured. With other things the same and within varieties, the small- 

 er berries are softened by frost more readily than the large ones and single berries 

 alone than those in clusters. 



l^These are air temperatures at the tips of the vines. The true freezing point of cranberries 

 ranges from 24.6° to 29.4°, but they will undercool a good deal without freezing if they are not 

 inoculated by jarring. Shaw Success (Massachusetts) and Metallic Bell (Wisconsin) have lowe r 

 freezing points than the other varieties so far tested. (U. S. Dept. Agr. Circ. 447, 1937, pp. 4 and 5. 

 Copy in the Middleboro library.) 



l^Conditions in this regard vary greatly from bog to bog and from year to year, vine coverage of 

 the crop sometimes being complete. Chances with expected minimum bog temperatures of 20° 

 to 21° F. may well be taken in October when this coverage is good. 



