Growing Fruit Trees
What Alaskan wouldn't like to go out to the backyard, or Back Forty, and pick a juicy apple off the tree? Unfortunately, except for southern Southeast Alaska where Malus diversifolia, the Oregon crabapple, grows, no native fruit trees are found in the state.
What factors prevent the survival of fruit trees in interior Alaska? As you might expect, extremely cold temperatures, coupled with the frequent occurrence of early autumn and late spring frosts, literally nips many fruit trees in the bud. Trees survive winter conditions in two ways--by ceasing growth in the declining days of summer and by hardening, which changes tissues from tender to tough. In fruit trees, different parts of the plant stop growth at different times. Vigorous shoots may continue to elongate later in the season than the buds. While a tree is in rest, the level of hardiness fluctuates. Apparently, decreasing day length and temperatures trigger the metabolic changes that bring about hardiness.
After initial hardening, increasing levels of cold resistance can be achieved, up to a point, by exposure to lower and lower temperatures. As temperatures rise in the spring or during a chinook in the winter, the tree loses its resistance to cold injury. A cold snap in the spring may cause injury at temperatures the tree could easily have withstood during the winter. Unfortunately for fruit growers, flower buds are among the first parts of the tree to lose their hardiness, and as buds develop in the spring, temperature gets more critical. Researchers have found that the difference between slight and severe injury may be only a degree or two at this time. A fruit grower might chance an early fall frost, but should consider taking some protective measures in the spring.
Fruit trees in interior Alaska can suffer from high temperatures also. This type of injury is called sunscald. On a cold winter day, the sunshine may raise the temperature on one side of the tree so high that thawing occurs. When the sun suddenly disappears, the temperature of the thawed portion may drop so rapidly that the cells cannot reharden fast enough to avoid injury.
In spite of all the problems with growing fruit trees, Carrol and Josie Phillips, Jr. of Fairbanks, prove it can be done. After twenty six years of experience, they have found that south facing, mid- to upper-slopes make the best sites for orchards. The use of hardy varieties grafted onto hardy rootstocks is also essential. The rootstock confers cold resistance, while the scion, or upper portion, is bred more for fruiting characteristics. The Phillipses have found Siberian crabapple (Malus baccata) a hardy rootstock for interior conditions, Heyer #12, Rescue, Osman and Anaros are generally good producing, hardy varieties when grafted onto Siberian crabapple. Because sunscald is a problem on south facing sites, they keep the trees bushy instead of pruning them to a single trunk. A smaller-diameter stem is not subject to the rapid thaw-freeze cycle, although support is needed when the branches are heavy with fruit--a problem most fruit growers in Alaska would like to have. The Phillipses protect their trees with steel barrels with the ends cut off. The drums keep out rodents, and keep in warmth around the tree.
