Frost and the Prevention of Damage by It. 25 



regard to surrounding topography. For deciduous orchards in the 

 colder sections there should be not less than 100 of the 5 -quart lard- 

 pail heaters to the acre, and if exceptional cold is likely to be expe- 

 rienced frequently, about 140 to the acre should be used. Of course 

 all the heaters are practically never lighted at once ; some are always 

 held in reserve to be used when others burn out. In the warmer de- 

 ciduous fruit regions, where the temperature is not likely to fall be- 

 low 25 at any time, these heaters should be set about 80 to the acre. 



N 



X 



I ^ * * \ * x ' x ** * x " x '*' "*' 



* . * . .*. . x . . x . . .* ' x @X * * * * x " " x " "x* "x 



. x . . * . . x . . x ! . x . X X ! x ." X. ! x " x ' * x 



X . .*. . X . . X . . X . , K . " x . x x ! x * '** *x' x 



. x . ! x . ! x . X ! x ! . x . . x . . x . X * x . x x 

 x . , x . **. . x . . x . ,' x . X x * x ' * x ' * x * * x * * x 

 x . . x . , x ! X X X X x * ' x x ' * x * x 

 x - x . x . . * . x . . x , , x . . x . . x * x * * x " ** 



x x x n x x x x x x*"x'*x* 





FIG. 10. Plan of lemon groves where temperature records shown in figure 11 were 

 obtained. Dots represent lemon trees, spaced 20 feet apart ; crosses represent high- 

 stack oil heaters. Squares marked H and C show locations of thermometers in heated 

 and unheated groves, respectively. 



The number should not be much less if 2-gallon lard-pail heaters are 

 used. The larger heaters have a longer burning time, but the amount 

 of heat released in a given time is not much greater. (See fig. 12.) 



The number of the newer improved type of heater necessary for 

 protection depends on the location of the orchard and on the kind of 

 fruit to be protected. Orange groves on low ground, where tem- 

 peratures as low as 20 may occur as often as every five or six years, 

 should have at least one large capacity heater to each tree. On the 

 higher slopes the number may be reduced to 80 per acre, but if ex- 



