This figure shows how important it is to keep your trees away from a frost 
pocket. By watching a row of thermometers all winter a United States Weather 
Bureau observer got these remarkable facts from a California hillside. 
The 
figures above the curve, which represents the slope of the hill, show the average 
temperatures at the different elvations for 45 clar nights. Figures below the 
line show temperatures for one clear cold night. The temperatures near the top 
show the “Thermal Belt” so common on mountain slopes. 
From Men & 
Resources, an interesting book by J. Russell Smith, Harcourt Brace & Co., N. Y. 
Trees in a frost pocket will have 
their leaves killed in the autumn so 
that they cannot mature their fruit, 
while the trees on the nearby hill can 
breathe on for two or three weeks 
longer and finish up their year’s work. 
These early autumn freezes that 
catch a tree while still in active growth 
are particularly destructive because the 
tree, being full of sap, may freeze and 
Split the bark. One year I had this 
happen to a number of Stayman Wine- 
sap apple trees under the following 
conditions. A careless stableman had 
manured them repeatedly through the 
summer because they were near the 
barn, and September had 11 inches of 
rain; in late October, an unusually 
early freeze. The heavily manured 
trees perished; the ordinary orchard 
escaped. But a few trees at the outlet 
of roadside drains had benefitted by 
an accumulation of soil and repeated 
soakings at every rain. They also per- 
ished of “winterkill.” Winterkill is usu- 
ally springkill or autumnkill. 
Second cause of winterkilling—late 
growth in autumn. See page 14 on 
English Walnut. 
The third reason why we cannot 
speak yet authoritatively about the 
northern limit of the Chinese Chest- 
nut is that different trees may differ 
in the length of the required rest pe- 
riod of the tree. Nearly all of our frost- 
climate trees need frost to put them to 
sleep in the autumn, and then they will 
stay asleep until they have had a cer- 
tain number of hours of cold weather. 
Now different species vary in the length 
of the required rest period. And in 
some species the different trees within 
the species vary in this respect. For 
example, the Elberta peach requires 
1000 hours of temperature at 45° F., 
or lower, during the winter to complete 
the rest period and resume normal 
growth under favorable spring temper- 
atures, while the Hiley and other va- 
rieties require 700 hours of tempera- 
ture of 45° F., or lower, in order to 
finish the rest period, which means 
that the Hiley will start growing in a 
warm spell in February, while the El- 
berta sleeps on, in warm winters. 
It seems to be true that some varie- 
ties of the Oriental Chestnuts have a 
shorter rest period than the American 
Chestnut. It will take a number of 
years and much experimenting to find 
out the exact facts in this field. In 
the meantime we cannot say for cer- 
tain that the Chinese Chestnut will 
grow in the exact northern limit of 
the American Chestnut. But I am pro- 
pagating one variety from a tree that 
has stood unharmed for many years 
in southern Connecticut, and another 
that stood the terrible Armistice Day 
