Suggested Means of Control
Since it is impossible to control temperatures and precipitation, it is perhaps a vain hope to expect complete immunity from winter injury to the English walnut. It is possible, however, to lessen the degree of injury by certain measures of precaution. These are as follows:
(1) Plant only the hardiest varieties.
The past winter showed very clearly that the commercial varieties of English walnut or seedlings as grown in this state are not hardy enough to endure the severe cold that periodically occurs in Michigan. This limits the choice of varieties to those from central Europe or north China where rigorous climatic conditions prevail. As already pointed out, the varieties that endured the past winter were from the Carpathian region in Poland or western Russia and north China. These varieties have not been widely distributed in this state and it may be found that even these will have a limited range in Michigan. Their behavior, however, shows that they are somewhat hardier than varieties from western Europe or England. Unfortunately the supply of trees of these apparently hardy kinds is limited and it will take some time to work up a stock of the best strains. In the meantime, those who desire to plant the English walnut had better wait until a supply of the hardier kind is available or plant some other hardy species such as the black walnut.
(2) Thoroughly drain all soils intended for nut trees. Well drained soils favor good root development and seem to lessen late growth, thus reducing to a slight extent at least the severe killing back that is noticeable on such growth.
(3) Use nitrogenous fertilizers in moderation.
Fertilizers rich in nitrogen may stimulate the late growth and predispose the tree to killing back.
(4) Do not cultivate the soil around nut trees late in the summer.
Late cultivation stimulates late growth and prevents the trees from properly ripening their buds and wood. This late growth invariably suffers more severely from winter cold than growth that is well matured.