34 MASS. EXPERIMENT STATION BULLETIN 402 



CRANBERRY FROSTS 



Cultivated cranberry bogs are made from the land of marshes, swamps, swales, 

 pond bottoms, or low meadows. They are always on the lower land in their 

 vicinity, and in Massachusetts they usually are largely surrounded by sand hills 

 (Fig. 3). Such locations are real frost pockets, for the air is often much colder 

 on clear cool nights over bottom lands than it is on adjacent uplands, especially 

 when there is little wind. This is due to the drainage by gravity of the surface 

 air of the uplands, cooled by conduction to the ground and other exposed sur- 

 faces, especially plant leaves, which radiate heat to the cold sky, down onto the 

 lower land.^^ Consequently frosts in May or June often kill vegetation on low 

 land and at the same time do little or no harm on the hills, especially on their 

 higher parts.'* The limit of injury is sometimes conspicuous as a contour line 

 along the uplands. 



It w411 be seen, therefore, that protection from frost is important in cranberry 

 culture. Most cultivated bogs are protected by flooding with water from streams, 

 ponds, or reservoirs. This flooding is done mostly by gravity, but a third of the 

 cranberry acreage of the State is flowed by pumping. Water supplies, however, 

 are often scant and must be used carefully. Also, frequent flooding in the spring 

 retards the new growth and tends to reduce productivity, and in the fall disturbs 

 harvesting. Accurate and timely frost warnings, therefore, are much desired by 

 cranberry growers. To provide them was one of the problems when the cran- 

 berry experiment station was established in 1910. 



The frequent failure of the Weather Bureau in its former predicting was due 

 partly to its lack of familiarity with cranberry frost problems, and the fine work 

 of Cox'^ on bog microclimate and frost conditions on the Wisconsin marshes was 

 a great help. General warnings of frost were inadequate, for they gave no idea of 

 the degree of cold expected. Facts given here about the frost endurance of the 

 vines and berries show how needful this close information is. Obviously, also, 

 frost warnings based on noon and especially on evening observations have some 

 advantage over morning predictions. 



Recent expansion of forecast services has made good advices and warnings now 

 available at the East Boston office of the Weather Bureau at any hour, day or 

 night. 



Spring Frosts 



Figure 4 pictures the dormant fruit bud in the tip of a cranberry branch, cut 

 open to show its center dead and dark from frost injury. The center always 

 darkens within a day after it is killed by frost. The inside of an uninjured bud is 

 green throughout. Except when the vines are winterkilled, these buds seldom fail 

 to stand all the low temperatures of winter. The writer has observed one case 

 and been told of others where they w-ere killed by temperatures below zero in 

 December after a very warm November, their centers turning dark as from frost 

 injury. 



Bogs varj' greatly in starting new growth, and early bogs in cold locations are 

 likely to be hurt by frost late in April. This is especially true of bogs in the 



l^For a full discussion of radiation, conduction, and air drainage in their relation to the formation 

 of a frost hazard, see Young, Floyd D.. Frost and the prevention of frost damage. U. S. Dept. 

 Agr., Farmers' Bui- 1588, pp. 1-4, 1935. (Copies in the Middleboro library.) 



'^^The temperature inversion at the Experiment Station often reaches 10° F. and sometimes 15° 

 in the first 18 feet above the bog surface. See Brooks, Charles F., Bui. Amer. Met. Soc, 16: 93-94, 

 1935; and Franklin, H. J., U. S. Monthly Weather Rev., Supplement No. 16, 1920, pp. 25-26. 

 (Copies in the Middleboro library.) 



l^Cox, Henry J., Frost and temperature conditions in the cranberry marshes of Wisconsin, 

 U. S. Weather Bureau Bui. T, 1910. (Copy in the Middleboro library.) 



