Plum tree, Prunus. A medium-grown tree which is found in the temperate climates of Europe, Asia, and North America. [1] Its stem is short and rarely upright; its crown is proportionately large but irregularly branching. The bark is uneven due to the fissures which develop early. The leaves are dentate, almost oval, and of an unpleasant green because they are often damaged by inclement weather in spring, and especially by insects. The white, rose-shaped flowers appear in April. The plums which follow differ in size, shape, colour, and flavour according to the cultivar; each fruit encloses a stone with a bitter kernel.

The plum is the most common stone-fruit tree. Its fruit keeps no better than other stone-fruits and must be eaten when ripe, unless it is cooked or dried. The plum thrives only in cultivated soil: in uncultivated ground, it languishes and soon perishes. It springs up in sites of any exposure and thrives in soil which is dry rather than damp, sandy rather than heavy, and above all in black sand. However, it can tolerate damp soil for a limited period. It generally adapts quite well to all cultivated soils because it has creeping roots, but it cannot tolerate clay, in which it makes no progress and bears worthless fruit. In soil which is completely dry and light or sandy and too superficial, it grows feebly and bears only poor, thin, worm-eaten fruit which generally falls before it is ripe. In clay and rich, heavy soil the fruit is less prone to fall or be worm-eaten but is unpalatable.

Plums may be propagated from seed and by grafting. The first method is used only in order to procure suitable rootstocks for grafting, since only a small number of medium-quality plums come true: most seeds produce plums which are wild and degenerate; it is true that a few may prove excellent, but this is a rare and chance occurrence. It is therefore customary to graft this tree in order to obtain the desired fruit, which is also perfected by grafting. The best rootstocks for grafting plums are the cherry and ‘Saint Julien’ plums. One may use cleft grafting or shield budding, but plums take again better and make more rapid progress when the first method is applied. Both rootstocks grow in any soil apart from soil which is too dry, light, or sandy, in which it is preferable to plant plums grafted on to almonds, since they do not grow suckers from their roots, which is burdensome and disagreeable. However, this graft rarely succeeds, because almonds do not take root again readily, especially when they have been transported from a distance. Plums may also be grafted on to peaches and apricots raised from seed, but these trees, since they are more delicate, need to be managed carefully and are not long-lived. See Tree nursery.

Plums can also serve as rootstocks for grafting peaches, apricots, almonds (which often fail), and the double-flowered dwarf almond, which takes again readily. One can also graft Saint Lucie cherries, cherry laurels, etc. on to plums, but the grafts and rootstocks perish the following winter. [2]

When removing plums from the tree nursery in order to plant them permanently, one should choose those which have been grafted for two years. If there are no plums of this age it is better to take maidens rather than trees which have been grafted for three years, since the latter are the least certain to take root again. Plum trees can be shaped into various forms in a garden, most commonly as standard trees, then in espaliers where most plums thrive better than as standards, and lastly as bushes which is suitable for every cultivar. Standards planted in the open ground are spaced at intervals of 12-15 feet, espaliers at intervals of 10 or 12 feet, and bushes at intervals of 15-18 feet, given that bushes grow vigorously and spread out more than plums grown as standards. These intervals should be regulated according to the condition and depth of the soil.

Plums grow good, strong, branching roots, which is why they take root again readily following transplantation. This tree is so hardy and well adapted to the climate of this kingdom that it should always be transplanted in autumn, when it will take root again more reliably than in spring and grow more vigorously in its first year, which is beneficial when establishing the desired shape of the young trees.

Of all stone-fruit trees, plums lend themselves most readily to being pruned. The only precaution one should take is not to prune excessively, for the more one cuts back the wood, the more gourmands it grows, until it becomes entirely exhausted, following which the gum begins to exude and the tree perishes. One should then tend the tree by detaching the gum and moss, removing the cankers and dead wood, suppressing the short, slender branches and branches of ‘false’ wood, and cutting off the diseased wood entirely.

The best plums are reserved for the table when they are ripe, while the remainder are used for making jam. However, by drying the former one can make excellent prunes, for which the largest, sweetest, and fleshiest plums are the most suitable. Damsons and the gum exuded by plums have some medicinal properties.

Plum wood is quite hard and marked with red veins: it is the most beautiful wood in our kingdom, which has caused it to be given the name ‘satiny wood’. However, it is little used because the American woods are infinitely superior in every respect. Plum wood is used for different purposes by turners, dealers in inlaid ware, and cabinetmakers. One may give it a fine red by leaving it to boil in lye or lime water.

Agricultural writers mention more than 250 different plums, of which there are fifteen or sixteen good-quality plums and about twenty which pass for being mediocre. Of the remainder, a dozen or so are good for making compotes or jams while the rest are little valued. The nature of this work does not permit us to enter into detail on the particular qualities of these different plums: see the catalogues of the R.R.P.P. Chartreux de Paris and abbé Nolin.

A few species of plum are of interest to collectors because of their singularity or decorative qualities, such as the double-flowered plum of which the fruit is excellent and the leaves very large, the perdrigon variegated plum of which the wood, leaves, and fruit are variegated, the stoneless plum which encloses a kernel with no bony wall, the English meloniform damson of which the leaf margins are white, and the Canada plum of which the flowers, which are tinged pink on the outside, are striking in spring. [3]

Notes

1. Prunus domestica, the common plum, is a cross between Prunus spinosa and Prunus cerasifera subspecies divaricata, known as Prunus + domestica (Huxley et al., 1992, iii.735).

2. The cherry laurel is Prunus caroliniana.

3. The Canada plum is Prunus nigra.