WINTER PROTECTION OF GRAFTS AND SEEDLINGS
It is not enough to make a successful graft and to watch it carefully during the growing season, picking all sprouts off the stock, spraying it so that insects will not chew the tender leaves and bark, bracing it against windstorms and perching birds. Each graft must also be protected from winter injury. For many years I have studied and experimented to find a successful way of achieving such protection. To enumerate my many experiments, from simple to far-fetched, would be to write another book quite as long as this one. My conclusion, now, is that there is little one can do to assist nature in the process of acclimatizing grafted plants and seedlings.
I have repeatedly noticed that the place where most damage is done by the cold is at the union between stock and graft. For example, I observed this on the European walnuts, imported from Poland, grafted to Minnesota black walnut stocks. Although both the buds and the wood of the top remained fresh and green, the unions suffered severe, and sometimes total winter injury. In grafts where the latter occurred, the dead cells soon caused the wood to ferment and sour. Occasionally, a small group of healthy cells succeeded in re-establishing circulation with the unharmed, grafted top and the graft, continuing its growth, would eventually overcome the injury it had suffered. I have seen this occur with grafts of English walnut, apricot and pecan.
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.
My last word of advice in raising what might be termed semi-hardy trees, is to grow them in sod, the ordinary quack grass, June grass, bluegrass or other natural grass sods which can be found on your planting site. Although this will probably hold back your tree development for a few years, until the roots are thoroughly established in the deeper soil beneath the sod roots, it is surprising how many species of trees will thrive in sod and perish on open cultivated ground. I can give no better example of this than relating a circumstance which bears this out in a most convincing way. In 1941 I purchased about 250 filbert seedlings from Samuel Graham of Ithaca, New York. These were planted out on a field site and practically all of the plants made good growth the first year. They were thoroughly cultivated. The next year a second batch of plants of a like amount were purchased from the same man and of the same kind of seedlings. Mr. Graham told me that these were seedling trees from Jones hybrid seeds which he had growing in his orchard. These plants were put on heavy sod ground; all plants were protected by screens, but the plants on the sod ground were subject to a very wet season and it was necessary to build up the soil around some of the plants in order to save them from being drowned out. Today about 45 plants are living on the sod culture and two or three barely alive exist in the open field culture. Although the plants remaining alive on the sod culture plot are almost pure filbert strain they are therefore very subject to the common hazel blight. Some have grown into bushes 10 feet high which later were hit by blight and have been reduced to small bushes. Others are producing good filbert-type nuts and are somewhat blight resistant, but the main fact to remember is that about 1/4 of the plants on sod culture lived, whereas not over 2% are alive of the open field culture plants. The distance between these plantings is approximately 1/8 of a mile. In addition to being placed in sod these filberts which have survived are sheltered by rows of evergreen trees both on the south and on the north side which may be construed as of some assistance but is not altogether the reason for the tremendous difference between the winter protection value of sod and open field culture. This is not the only example that I could cite but is one of the most outstanding ones which has come to my attention. Sod culture is now being recommended to fruit orchardists in this part of the country and in my own experience, I can highly recommend it for apples, plums, pears, mulberries and nut trees.