A blackbird’s nest in the crotch of a small tree suggested to me the most satisfactory guard I have yet found against this greatest of dangers to all exotic, grafted varieties of nut trees.  The nest, which enclosed over half of the graft union, was partly composed of woolen fibers which its builder had gathered from barbed-wire fences that sheep had brushed against.  On the exposed portion of the graft union, discoloration indicated injury and dead cells, but on that part covered by the nest, all the cells were alive and green.  I have improved on the bird’s nest by wrapping a large wad of wool loosely around each graft union.  The value of wool is that it will not collect moisture and so start fermentation.  It allows the cells to breathe, yet protects the union from the shock of temperature extremes.  Birds will inevitably steal some of the strands of wool but this activity in and about the trees means a decrease in injuries from insects—­a worthwhile exchange.

When an unusually large swelling at the graft union appears, it is certain that the plant needs protection such as I have described.  Such swellings result from a too-rapid multiplication of cells, a condition which leaves the union weak and susceptible to injury.  Although a union is never entirely safe, even after many seasons of growth, each year adds to the safety factor by the development of rough, cork-like bark.  I suggest the use of a woolen guard for several winters, by which time this outer bark should be able to do its protective work alone.

A successful but rather expensive method of winter protection, both to the graft itself and its union with its host, is to enclose the entire tree with a box-like structure consisting of four corrugated aluminum roofing sheets set up on their ends and countersunk into the ground about six inches.  The purpose of countersinking these below the ground surface is two-fold:  it stiffens and braces the structure and prevents the intrusion of mice and other rodents, which may also appreciate both the shelter and possible food supply contained therein.  By fastening these sheets together with a stout wire you can depend on the structure to stand up against wind and snow pressures.  Fill the entire inside with forest leaves, oak leaves preferred, as their insulating quality is the best and they are slow to rot and ferment.

When working with semi-hardy plants in a cold climate, avoid fertilizing and cultivating the ground after the first of August.  Doing so stimulates late growth and such growth is very likely to be badly injured during the winter months.  If fertilizer is used, it should be early in the spring, as soon as the ground is free from frost.  Trees which persist in growing late into the fall are more subject to winter injury.  Protective measures to avoid their doing so by inducing an earlier dormancy, include keeping the soil around them dry and exposing, somewhat, the roots near the trunk of each tree.