Frost and the Prevention of Damage by It. 13 



completely cut off, which permits of a slow thawing of blossoms and 

 fruit after a heavy frost. This reduces the amount of injury. 



Orchard heaters burned under screens of lath or cloth are more 

 effective in raising the temperature than is the case when they are 

 burned in an uncovered orchard. 



Other Methods. Paper covers may be used to protect small indi- 

 vidual plants or large paper strips may be used to protect gardens 

 against light frosts. Generally speaking, paper coverings do not 

 afford as much protection as those made of cloth. 



Young potatoes and garden truck are sometimes protected by 

 plowing a furrow between the rows and covering the plants with soil. 



Cranberry growers in the marshes of Massachusetts, New Jersey, 

 and Wisconsin flood the marshes with water from large reservoirs 

 when frost is expected. For protection against a light frost it is 

 generally sufficient to raise the level of the water in the ditches. For 

 a moderate frost the water level is raised to the surface of the bog 

 and when a heavy frost is expected the vines themselves are covered 

 with water. In the first two instances protection is afforded by the 

 heat given off by the relatively warm water. 



Devices for Adding Moisture to the Air. Smudge fires of damp 

 straw or manure have been used to create a blanket over the area to 

 be protected, the object being to decrease the radiation from the 

 ground rather than to add heat to the air. It is possible that such a 

 method may be successful when the air is calm and is already nearly 

 saturated with moisture. However, heavy frosts generally occur 

 when the humidity is fairly low and a perfectly calm surface air is 

 seldom met with on cold nights; there is usually at least a slow 

 movement down gently sloping valleys or plains. In a relatively dry 

 atmosphere any moisture thrown off by damp smudge fires will be 

 rapidly lost by circulation and diffusion into the great quantities of 

 air above and surrounding it, and the effect in diminishing the rate of 

 radiation, will be very small. At the same time, if an effective 

 blanket of moisture could be spread over the orchard, a slight breeze 

 would carry it steadily away, replacing it with cold outside air that 

 has been chilled through contact with soil from which radiation had 

 gone on unchecked. 



Spraying of trees to afford protection from frost has been at- 

 tended with some success. However, it is not possible to combat a 

 heavy frost in this way on account of the heavy coating of ice formed, 

 which strips leaves and even large branches from the trees. If the 

 tree is in bloom the water is likely to cause damage by interfering 

 with pollination. These objections do not have so much weight in 

 the case of protection of garden plants, and spraying with water may 

 be very effective where these are concerned. 



