Protection against frost is not only possible, but practicable. The method to be employed depends on the kind of crop, the expense its value will justify, and the facilities at hand. But whatever method is chosen, it must be carried out systematically, intelligently, and with thoroughness if satisfactory results are to be obtained.
Progressive cranberry growers resort to three expedients to ward off light frosts, aside from flooding, which is practiced in the spring and autumn and also when exceptionally severe frosts are expected. These methods are cultivation, drainage, and sanding. By cultivating the marsh and keeping it free from weeds, moss, and other vegetation, the heat from the sun more easily penetrates the soil, and there is, therefore, more heat to be given off when needed to prevent frost during the night. Good drainage decreases the effect of cooling by evaporation, and a dry soil becomes warmer under sunshine than a wet soil, and therefore radiates heat more freely into the air at night when needed to ward off frost. A covering of sand lowers the specific heat of the soil, and thus stores up a large amount of heat during the day to be given to the air at night. In the Cape Cod marshes it is the practice to spread about half an inch of sand over the surface of the marsh each year. These methods, when systematically and carefully carried out, are usually effective in warding off light frosts that are liable to occur between early spring and autumn.
Smudging has been practiced for many years in the trucking sections of the Southwest, as well as in the fruit-growing districts of California and Florida. The object is to cover the garden or orchard with a thick blanket of smoke and vapor, with a view to checking radiation. The success of this method depends upon the care and thoroughness with which it is carried out. The cloud of vapor or smoke must cover the garden or orchard, and be dense. A thin blanket will not be sufficient. The fire should be built on the windward side of the orchard, and such material used as damp straw, prunings, manure.
If the fire burns briskly, it may be sprayed with water to increase the cloud of vapor.
Portable smudges have superseded the stationary smudge in many places. They possess the advantage of being moved from place to place, thus overcoming the effect of a change of wind, which often renders the stationary smudge ineffective. Any sort of a fire-box that can be placed on a stone-boat or sled will answer the purpose.
The most effective method, and the one now practiced by the large fruit-growers of Colorado and California, is the distribution of a large number of small fires, about forty to the acre, throughout the orchard. In this case dependence is placed in the direct heat given off by the fires as well as in the cloud formed from the smoke. Coal is the fuel most generally used in California, while oil is coming into use in Colorado. When coal is used, it is the practice to suspend wire baskets a few feet from the ground, containing ten to twenty pounds of coal, which is lighted when frost threatens. Forty such baskets will raise the temperature of the orchard three or four degrees. The cost depends upon the price of the fuel. In California a ton of soft coal that costs $2.50 was considered sufficient for one acre each night.
Some orchardists have replaced the coal baskets with oil burners. This method is more expensive to install, as the burners are more costly than the baskets, and tanks must be provided for the storage of the oil; but it is said to be much more convenient, and quite as efficient. At the Hamilton fruit ranch, near Grand Junction, Col., the temperature in an orchard of twenty acres was maintained at 33° by the use of oil burners, while a minimum temperature of 27° was registered in surrounding localities. The cost of the protection of this orchard for four nights when frost occurred in the vicinity was approximately ten per cent of the value of the crop. Methods less systematic than the above are usually disappointing. (For another discussion, see Paddock and Whipple, "Fruit-Growing in Arid Regions.")