64 MASS. EXPERIMENT STATION BULLETIN 402 



Cox indicated that sand protects from frost better when dry than when wet^" 

 and gave data supporting this view. The writer questions this,^^ and the general 

 experience of cranberry growers is that sand is a better protection when wet. 

 Apparently Cox failed to appraise properly the relations of water to the conduc- 

 tivity and specific heat of soil and magnified the effect of evaporation. Resanding 

 is practiced generally on Massachusetts and Wisconsin bogs, but less elsewhere. 

 It has important uses besides frost protection. ^^ 



Flooding 



Partial flooding where water is available has long been the main protection 

 from frost used by cranberry growers everywhere.^^ Because of its high specific 

 heat, 2 or 3 inches of water everywhere under the vines is enough, for heat passes 

 by radiation, conduction, and convection from the water to the air and keeps 

 the vines from freezing. Some claim the vines must be submerged under extreme 

 conditions, and this may be necessary on rare occasions in April and October 

 when the water is cold. Mere filling of the ditches is never any protection beyond 

 a few feet from the water. If water supplies are limited and it remains cold, the 

 water may be held over on a bog from one night to another for a few successive 

 days up to about May 10 and for a day at a time after that.^"* It may also be 

 held over for a day or two in the fall, but this tends to impair the keeping qual- 

 ity of the fruit. Stop-waters in bog ditches (Fig. 13) often help greatly in effi- 

 cient use of limited water supplies in frost flooding. The service of reservoirs 

 is often greatly extended by pumping the water used in flooding back into them 

 again and again. If the winter flowage is held till May 25, new growth usually 

 will not start enough to be hurt by frost before the end of the month, and harmful 

 frosts come in June only occasionally. This is often a good practice if there is no 

 water for reflooding; but it is better, if possible, to save the winter water for this 

 purpose by pumping. If a reservoir cannot be prepared to hold this water, the 

 bog can often be divided with a dike so that the winter water may be held late 

 on each half in alternate years and be pumped from one to the other for frost 

 protection. 



It is better in the long run to chance moderate losses by frost than to waste 

 water and reduce the crop by flooding too often. Most growers with bogs in 

 warm or even average locations in southeastern Massachusetts will probably 

 fare much better in the long run if they flood only when the difi^erence between the 

 wet-bulb temperature and the dew point toward the coast and inland is greater 

 than that between the dry-bulb and wet-bulb temperatures in the same places. 

 Frost flooding should never be done anywhere when the difference between the 

 dry-bulb and wet-bulb readings is more than one degree greater locally than that 

 between the wet-bulb temperature and the dew point. 



^"Cox, op. cit., p. 61. 



9lMass. Agr. Expt. Sta. Bui. 160, 1915, pp. 92-93. 



92Mass. Agr. Expt. Sta. Bui. 371, 1940, p. 23. 



^^Mass. Agr. Expt. Sta. Bui. 371, 1940, pp. 7, 8, and 22. 



^''Much injury from flooding for 40 hours in the cool and clear weather that usually prevails in 

 a period of frost danger is not likely to occur on most bogs, even with the new cranberry growth 

 in its most tender condition. As a flood of this duration is always an effective treatment for the 

 blackheaded fireworm and other pests commonly abundant on the bogs in the spring, it should 

 be used against frost and insects at the same time whenever there is the chance, unless the bog 

 has a bad record for injury by flooding. 



