CHAPTER XII 

 SPRING FROSTS 



OF the numerous considerations which should influence a 

 fruit-grower in the choice of a situation, one of the most impor- 

 tant is the liability of the position to spring frosts. The Woburn 

 Farm offered special facilities for investigating the incidence of 

 such frosts, but, unfortunately, the work initiated on the subject 

 was cut short, owing to the exposure entailed in taking observa- 

 tions having proved nearly fatal to the manager, and other 

 circumstances have interfered with the resumption of the work 

 until quite recently. 



Injury to fruit blossoms occurs whenever the temperature is 

 lowered to such a point that the contents of the cells freeze 

 and the cell-walls are ruptured : this temperature is, accord- 

 ing to Church and Fergusson, 1 27 F. when the trees are in bud, 

 29 when they are in blossom, and 30 when the fruit is setting. 

 A lowering of temperature may occur under two essentially 

 different types of meteorological conditions : either during wind- 

 frosts, or radiation-frosts. In the former, the temperature of 

 the whole air is sufficiently low to cause freezing, and the cooling 

 effect is augmented by cold winds, generally from the north or 

 east ; in the latter, the cooling occurs at and near the ground level 

 only, and is due to heat being radiated into space at night by 

 objects on the earth when the air is clear and still. 



Very little can be done to mitigate the damage caused by 

 wind-frosts, except by sheltering the trees from the winds, either 

 by establishing the plantation in a situation where protection 

 from the east or north is afforded by natural objects, or by 

 interspersing shelter hedges throughout the ground, to act as 

 wind-breaks. Heating the air by fires made to the windward 

 of the plantation is, however, sometimes resorted to in the 

 United States, though the results are poor whenever the velocity 

 of the wind exceeds certain very moderate limits. At the 

 Woburn Farm some thirty shelter hedges were planted, all con- 

 sisting of fruit trees of different descriptions, and all of them 



1 Agric. Expt. Station of Nevada, Bulletin 79, 1912. 



124 



