The Horse plum was formerly used as a stock by nurserymen a great deal but is now wholly superseded. Indeed, it is so nearly lost to the trade as to make it almost impossible to really know what the plum of this name is. Some describe it as a small-fruited Domestica, others as an Insititia similar to the St. Julien, but the majority of the trees shown by old nurserymen in the nursery region of New York, about the only place in which the stock was used, show it to be a Cerasifera but not Myrobalan. Some of the named varieties of Cerasifera probably sprung from sprouts of this stock. It seems to have had no qualities which would make it worth while to attempt to re-establish the stock.
The testimony of a large number of nurserymen is in favor of the peach as a stock for plums. Budded on the peach, plums of many varieties are grown very successfully on the warm sandy and gravelly soils so well suited to the peach. This stock enables the tree to make a quick growth and come into bearing early, and the roots do not produce sprouts. The budding with the peach is easily done, the young trees make a vigorous growth in the nursery and plums on peach roots can probably be grown at a less cost than on any other stock. Triflora plums in particular make excellent trees worked upon peach stock, the roots are as hardy as the tops and the union is sufficiently congenial to make the resulting tree long-lived. For the Domestica and Insititia plums the peach stock is not so valuable, for with some varieties a good union is not secured and the roots are less hardy than the tops. Among the varieties which nurserymen say will not unite with the peach are: Lombard, Damsons, Yellow Egg and Washington. Peach borers are sometimes troublesome when plums are budded on peach stocks.
Mr. Kerr, in his statement regarding stocks, on [page 115], says that it is his practice to whip-graft the plum on “whole-root” peach roots obtaining eventually the plum on its own roots. This method is certainly well adapted to Mr. Kerr’s conditions but whether it would do in heavier soils and a colder climate is doubtful. One would suspect that some varieties of Domesticas and Insititias at least would sprout badly.
In the South, more particularly Texas and the Southwest, Marianna stocks find favor, though their use seems to be on the decrease. The advantages of this stock are such as appeal to the nurserymen rather than to the plum-grower. These are that the Marianna readily strikes root from cuttings and the growth in the nursery is all that can be desired. Cuttings strike more easily in the South than in the North, hence its popularity in the first named region.
For the colder parts of the Great Plains and as far east as to include Wisconsin, Americana seedlings are the only stocks that will withstand the winter. In this region Americana stocks are, of course, used only for the native plums and data seem to be lacking as to whether other plums cultivated for their fruit could be grown on this stock or not. The W. & T. Smith Company of Geneva report that they are now using Americana seedlings for native plums for their eastern trade, speaking of them as follows: “We think we get a larger growth and a better root system by using the native (Americana) stocks. We also consider that the Flowering Almonds, Prunus triloba and Prunus pissardi, make a better growth on native stocks.” From the last statement one would suspect that it would be feasible to grow other orchard plums than the native species on this stock. As yet Americana seedlings are expensive, and until they cost less their use in competition with the Myrobalan and peach stocks will be almost precluded. The chief fault of the Americana stock is that the trees sucker rather badly.
Besides the plants discussed above various nondescript members of the genus Prunus are used as stocks for cultivated plums under particular circumstances or for particular purposes. Seedlings of Munsoniana plums are supposed to be preeminently adapted for low wet lands. J. W. Kerr believes that seedlings of Prunus hortulana are excellent stocks for native plums as they never sucker.[152] The Sand plum (Prunus angustifolia watsoni) offers possibilities as a stock for dwarfing larger growing species. According to Hansen,[153] who reviews the literature and describes several experiments of his own, the western Sand cherry (Prunus besseyi) dwarfs varieties worked upon it and has the merits of being extremely hardy and of producing trees which bear early and abundantly. As stated in the discussion of Subcordata, stocks of this plum have been used on the Pacific Coast and discarded because it dwarfs trees and suckers badly. According to Wickson,[154] the apricot and almond are sometimes used as stocks for plums in California and in some instances with considerable success.
Lastly, suckers are not uncommonly used by plum-growers for certain varieties. Thus in the western part of New York, the plum-growing region of the East, several varieties as the Reine Claudes and some of the Damsons are propagated from sprouts taken from the base of old trees. This method can be used, of course, only when the trees are grown upon their own roots. The writer was told by plum-growers in Germany and France that most of the plums in gardens and small plantations, constituting the majority of the plums in the two countries, were propagated from suckers. This method has small merit except that it enables a grower to get a few trees cheaply and perhaps gives a better tree of some varieties for a heavy soil. Beyond question it gives trees with a tendency to sucker—an undesirable attribute.
In the horticultural literature of the time recommendations for top-working plums are rather frequent. It is true that many varieties of plums grow slowly and make crooked growths, especially in the nursery, but in the attempts at grafting in New York the failures are more conspicuous than the successes. If top-working is decided upon, the earlier in the life of the tree it is done, the better. For the Domesticas at least, the Lombard is probably the best stock. The method of top-working is to graft in early spring or bud in late summer. Grafting ought to be used more often than it is to renew the tops of injured trees, as the difficulties in doing this are not much greater than in the case of apples.