It has long been known, especially in Florida, that some varieties flower profusely but fail to develop any fruits. In other instances, though good crops are produced one season, yet the following year there is no fruit, even though climatic conditions may appear to be identical. This peculiar behavior was not understood until Hume showed that it was due to faulty pollination. In the Journal of Heredity for March, 1914, he writes:
1 Bull. 99, La. Exp. Sta.
"It was not until 1909 that attention was called to the true cause of barrenness in D. kaki, and the year following the cause of sporadic fruitfulness was learned. It was known years before to a few that the flowers of D. kaki are of two kinds, pistillate and staminate, but that this fact had any practical bearing on the problem of unfruit-fulness did not seem to occur to anyone. More recently the existence of perfect flowers, i.e., those containing both stamens and pistils, was brought to light. These flowers have no practical bearing on the problem, as they are rare, and from some cause or other not yet clearly understood, their ovaries very seldom develop into mature fruit. Since 1909, the results of more than twenty thousand hand pollinations have fairly demonstrated that pollination will cause fruit to set and grow to maturity, when without it no fruit would be produced.
"The fruitfulness of certain trees or groups of trees in some seasons and not in others, even when pistillate flowers were present in goodly numbers each season, can now be explained by the fact that there are certain horticultural varieties of D. kaki which produce staminate flowers at irregular intervals. They may be found on certain trees one season and not the next. Many seasons may elapse before they appear again. It may even happen that never again are they produced, or they may be produced every other season. Many combinations of intervals or skips in the production of staminate flowers are possible and probable. A number of them have been observed and noted with references to particular trees. The staminate flowers, when they occur on these trees, are abundantly supplied with pollen and fertilize not only pistillate flowers on the same trees, but through the agency of insects the flowers of many trees surrounding them."
It was evident to Hume, therefore, that a variety was needed which could be depended on for the production of pollen to fertilize the flowers of trees which lacked the male element. The search for such a variety brought several to light, and one of them, the Gailey, is now recommended for planting as a pollinizer. By setting one of these trees to seven or eight of other kinds, productiveness is insured. Hume continues:
"It must be emphasized that the behavior of D. kaki in its relation to pollination, or of any other fruit for the matter of that, in any one locality, is no index to its behavior under any other set of conditions. Even though the conditions may appear to be the same, there are differences which we are too dull to detect or too ignorant to understand, but which nevertheless operate on the trees and influence the results. It is a matter of observation that under certain local seasonal and climatic conditions some varieties of D. kaki will set good crops of fruit without pollination (seedless of course) while under another set of conditions they do not do so. One season they may bloom freely and set all the fruit the trees should carry and with an equal amount of bloom in another season the same trees may bring no fruit to maturity.
"To sum up conditions as they are at present in the Lower South, and based on numerous observations extending over more than a decade, it is a fact that trees of all varieties of D. kaki, in good health and which bloom under normal weather conditions, can be depended upon to bear good crops if pollinated and it is equally true (a few varieties only excepted) that they will not do so if pollen is not provided. In the last two seasons it has been amply demonstrated that all that is necessary is to have staminate flowering trees in proximity to the pistillate ones and bees, wasps, flies and other insects will take care of the problem according to nature's own plan.
"What is the owner of an orchard already planted to do if he desires to place pollinizers in his orchard? It is quite easy to bud over branches here and there in properly placed trees. No preliminary cutting back is necessary, as the buds may be inserted where the bark is anywhere from one to three years old. The work should be done just as the leaves are coming out in the spring, using the ordinary method of shield-budding, and tying the buds in place with waxed cloth. The wraps should be left on about three weeks and as soon as the buds have taken, the branches should be cut back, leaving stubs five or six inches long to which the shoots from the buds may be tied as they grow out. These stubs should be removed at the end of one season's growth."
It may be mentioned that Tane-nashi, normally a seedless variety, fruits well without pollination, and it is thought that Tamopan may do the same.
The question of pollination is probably less important in semi-arid regions, such as California, than in the moist climate of Florida. The prospective grower should in any event use care in the selection of varieties, and satisfy himself as to the need of supplying pollinizers for them, before he undertakes to develop a commercial kaki orchard.
Horticultural varieties of the kaki are commonly propagated by budding and grafting. Several species of Diospyros are used as stock-plants.
The Chinese ring-bud or graft their plants upon the ghae tsao (Diospyros Lotus) and other species. The Japanese graft upon D. Lotus, on the shibukaki (an astringent variety of D. kaki), and occasionally on seedlings of the common sweet-fruited kaki. Ikeda states that stock-plants must be three years old and that grafting is done in early spring, using cions which have been stored for some days. Sauvaigo says that in southern France the kaki is grafted upon D. Lotus, D. virginiana (the common persimmon of the southern United States), and one or two other species. Crown-grafting and other methods are used, and the work is done in autumn or spring.
Hume considers that the best stock-plant for the southern United States is the common persimmon (D. virginiana), since it is more vigorous and produces a larger tree than other species. D. Lotus has been used in California but its value is not yet fully determined. Frank N. Meyer says of it: "As a stock, this persimmon may give to its grafted host a much longer life than the native American persimmon seems to be able to, for in China all the cultivated persimmons (kakis) grow much older than they do in America. Of some varieties there, one finds trees grafted on D. Lotus that are centuries old and still very productive."
Bailey writes: "The best method of propagating Japan persimmons is by collar-grafting upon seedlings of the native species (Diospyros virginiana), which are grown either by planting the seed in nursery rows or transplanting the young seedlings from seed-beds early in the spring. The seedlings can be budded in summer, and in favorable seasons a fair proportion of the buds will succeed. Thus propagated, the trees seem to be longer-lived than those imported from Japan. Inasmuch as the native stock is used, the range of adaptation as to soils and similar conditions is very great. As a stock, Diospyros Lotus is adapted to the drier parts of the West, where D. virginiana does not succeed."
Both cleft-grafting and whip-grafting are employed in Florida. Whip-grafting is considered best if the stock-plants are small. California nurserymen use the same methods and make a point of placing the graft as close to the root as possible.
Kaki trees begin bearing when three or four years old, and, proper attention being given the matter of pollination, produce heavy crops of fruit. Indeed, it is usually necessary in California to thin the fruit lest the trees injure themselves by overbearing. Pollination has been discussed on a previous page.