ORCHARD HEATING 21 



blanket or the liberation of heat of condensation at tempera- 

 tures above the freezing point. 



But all these "signs" are only so many admonitions to be on 

 one's guard in a matter where the price of success is eternal 

 vigilance; they may be ever so helpful, but they are not infal- 

 lible, (m) . 



Automatic frost alarms that can be purchased for about $45 

 may be set for a definite temperature and when this thermome- 

 ter in the orchard cools to this temperature a bell will ring in 

 the house. 



WHEN TO LIGHT THE FIRES 



It has been observed that after the temperature of the 

 orchard has fallen below the danger point it is very difficult to 

 raise its temperature, but if a moderate amount of heat is sup- 

 plied at a temperature of about 30o F. and this amount be 'grad- 

 ually increased as the temperature outside the heated area falls, 

 the temperature in the orchard is thereby kept constant and 

 above the danger point and thus the chances of the crop being 

 saved are greater. At first only every second or third row of 

 pots is lighted and then the thermometers are read. The others 

 are lighted as they are needed. If heating is done at all it 

 should be done with care and intelligence. The facts are that 

 the buds are much hardier than most people think and many 

 people have heated their orchards when the crop would have 

 been saved without heating. 



"A reading of the popular literature on the subject is likely 

 to cause one to infer that the buds have a certain freezing tem- 

 perature and that when they arrive at this temperature, they 

 all freeze. This, of course, is wide of the truth. There is a 

 range df four or five degrees between the highest temperature at 

 which two or three per cent of the buds are injured, and the 

 temperature at which all the buds are killed. It should be re- 

 membered that on the same branch are often found buds that 

 have swollen but slightly when others are in full bloom. A 

 freeze or two in the early spring will usually do no harm ; they 

 simply serve to thin the buds out, for it is generally known that 

 there are many times more buds on the trees than actually 

 mature into fruit. The number that one can allow to freeze and 

 yet not heat the orchard will naturally depend on how many 

 there happens to be on the tree at this particular time. It is 



(m). Papers on Frosts and Frost Protection in the .United States, 

 Monthly Weather Review, p. 565. Oct. 1914. 



