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.
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.