Factors That Influence Nut Production
W. B. WARD, Extension Horticulturist, Purdue University, Lafayette,
Ind.
The profitable production of fruit on nut trees under cultivation has no doubt been influenced by several factors. Assuming that the present-day seedlings and propagated varieties are winter hardy and the tree of bearing age, 10 to 15 years old, one may expect a reasonable harvest. It is somewhat disappointing to the owner of a single nut tree or for the grower on a semi or commercial basis to find that the tree or several trees have failed to set fruit.
The commercial fruit grower of apples learned, many years ago, that certain varieties when planted in solid blocks failed to set satisfactory crops. Rather than lose several years of growth and expense, the better growers top-worked the trees with a good pollinizer. The result was a profitable harvest of red and yellow apples, or varieties of different maturity. The peach grower liked the looks of a very fine peach and after a short trial found that the variety was not hardy enough to withstand the winter and early spring temperatures. The experiences of the commercial fruit growers could be well used by the nut grower. Only trees adapted to local conditions should be planted regardless of the recommendations of the nurseryman. Hardiness of wood and bud, ample production of pollen, reasonable climate during the growing season, and the control of insects or diseases determine, for the most part, the success of the harvest.
Soils and Fertility
The nut trees require good drainage and a good supply of moisture. A reasonably fertile soil should be selected for a planting site but through mulches, manures, and commercial mineral fertilizers any soil may be built up to a high state of fertility. A weak tree has little chance and may come into bearing too late to be of value for the present owner. The annual growth should be checked each year and, unless 10 to 12 inches of growth has been made the previous year, some means of stimulating more growth should be employed. The hickory, pecan and black walnut, as a rule, make little new annual growth while the Persian or Carpathian walnut, heartnut and chestnut ordinarily produce good annual growth and an abundance of good foliage grown where it counts the most, on the new wood.
Those who have observed the growth habits of nut trees know that the catkins are found on last year's growth, or two year old wood, and the fruiting flowers at the end of the present season's growth. There are times when the new growth developed in a matter of a few days to sometimes as long as two weeks. During the period of prolongation of the new growth and the formation and receptiveness of the pistillate flower much can happen. The catkins shed pollen when the temperature and atmospheric conditions are normal. Many times the pollen is dispersed before the pistillate flowers are formed.
Cross vs Self-Pollination
There is no assurance that a nut tree which fruits on the average of eight out of ten years will continue to do so in the future. Occasionally trees take on an alternate year bearing habit that could be caused from injury, insect or disease damage, or the relocation of plant food. The nut trees on their own roots should do better than when grafted or budded. The compatability of stock and scion is yet to be worked out and any constriction at the union may alter the fruiting habits.
The possible sources of pollen for hickory and pecan are from self-fertile trees, seedlings, and various natural crosses that may or may not produce edible fruit. The walnut family, which includes the black and Persian or Carpathian walnut; butternut and Asiatic nut (heartnut) have been used as pollinizers on the Persian walnut with some success. The butternut is the first to shed pollen in Indiana with the catkins dropping, in some years, by late April and the first week in May. Some years the black walnut has produced the peak pollen from May 5th to 12th but during the spring of 1953 the Thomas, Stabler, Rowher, Ohio and Stambaugh dropped the pollen from May 18th to 22nd. The Asiatic walnuts were in full bloom on May 14th and 15th. The above dates do not correspond to observations of other years, except for the butternut. The pistillate flowers on the Persian walnuts were fully opened by May 16th. The catkins of the Persian trees had dried by May 12th. Catkins from the Asiatic walnuts were kept fresh and distributed throughout two Persian walnut trees and by mid-afternoon a heavy rain came. On May 18th a few catkins were again removed from the Asiatic walnut and only enough for one Persian walnut tree were found and hung in the tree. The first tree has no fruit while the second tree has a fair crop in the making.