TUALATIN VALLEY NURSERIES, SHERWOOD, OREGON 
WINTER INJURY 
Weather conditions have killed and injured more fruit trees than 
all other causes combined. We consider the most dangerous season of 
the year to be in very early spring when we have bright, warm sunny 
days, followed by frosty nights, the warm rays of the sun starts the sap 
on the south sides of the trees. These clear days of February and early 
March are followed by frosty nights, the frost clinging to the bark chills 
the freshly risen sap, which soon becomes sour, often bursting the bark 
on the south sides of the trees and causing a gum-like substance to issue 
forth. This is soured sap, caused by thawing and freezing and may be 
prevented to some extent by shading the south sides of the young trees 
with a board or shake. These should be 5 inches wide, 3^2 feet high, 
% to 1 inch thick, sharpened at one end and driven into the ground 
about 6 inches from the tree, always on the south side so as to keep the 
sun rays from starting the sap prematurely. These protectors should 
be used for the first three years, after which the bark on the trees will 
have become thicker and will better withstand the sudden changes of 
temperature. The protectors may be removed during the summer 
months, or after danger of frosts is over. Sweet Cherry, Apricots and 
Peaches are the most easily affected. However, no harm will be done if 
the protectors are used on all young fruit trees. 
The Oregon Agricultural College advises a liberal coat of whitewash 
as a protection for orchard tree through the winter. This may be ap¬ 
plied on the larger limbs as well as the body, but in young trees would 
suggest that you also use the board or shakes in order to keep the sun 
off of the south sides, for we are certain that the premature action of 
the sap, caused by the sun is the start of the damage caused by the 
freezing that follows. By using both the whitewash and the boards, one 
would have double protection. 
Block of young Apple Trees, taken when half grown. 
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