WINTER INJURY 273 



242. Topography of land. — While it would seem patent 

 to all careful observers that low lands suffer much oftener 

 from frosts and freezes than the higher elevations, yet many 

 orchards are located unfavorably in this regard. While 

 the average temperature of the air decreases at the rate of 

 1° F. for each 300 feet of elevation above sea level, yet it 

 does not follow that more injuiy from low temperatures 

 occurs at the higher elevations. The disturbing factor of 

 wind and the fact that cold air will settle and flow down hill 

 accounts for the apparent contradiction. Here again, or- 

 chards located on high elevations are sometimes injured more 

 than those at lower levels during severe winters; however, the 

 reverse of this is true on the average. Frost pockets, coves, 

 and flat low lying lands are to be avoided for orcharding. 



In some of the western fruit sections, the reverse of this 

 principle holds true, owing to special conditions. In some 

 of the narrow river canyons, the fruit-trees suffer less from 

 injury in the winter and from spring frosts and ripen their 

 fruit from one to two weeks earlier than those planted on 

 the land along the "rim rock" or at a distance from the can- 

 yon. This phenomenon is explained by the fact that the 

 rocks of the canj^on walls hold the heat, are dark colored and 

 hence absorb a maximum of the sun's rays, and that there 

 is a "draw" of air down the canyon that wards off frosty 

 conditions. 



243. Winds. — While winds play an important role in 

 frost prevention, they also are a factor in augmenting win- 

 on the coast. Yet in the severe winter of 1917-18, the effect of the 

 water was insufficient to prevent the winter-killing of a well-cared-for 

 young orchard within sight of the open water. The slope was a gentle 

 one to the coast line, yet such hardy varieties as Wealthy and Mcintosh 

 were killed as readily as the tender ones, such as Baldwin and Wagener. 

 The ground was bare at the time of the low temperature in December, 

 and hence the root-killing was extensive. 



