There is no genus of flowering trees which contributes so much to the beauty of English gardens in March, April, and early May as Prunus. Following the now generally accepted signification of the word, not only the plums (or Prunus proper) are dealt with under this heading, but the almonds and peaches (Amygdalus), apricots (Armeniaca), cherries (Cerasus), bird cherries (Padus), and the cherry laurels (Laurocerasus) also. With even this extended interpretation the genus is well distinguished by its fruit, which is always a one-celled, one-seeded drupe. The leaves are alternate, either deciduous or evergreen; the flowers white or rose-coloured, rarely yellowish; petals five, calyx five-lobed, stamens numerous.
In order to facilitate recognition of the species it will be necessary to denote the characters roughly distinguishing each subgenus and section. It should be said, however, that some species (perhaps hybrids) are of uncertain position.
Plums and Apricots
Axillary buds solitary. Terminal bud present. Flowers solitary or in clusters of two to four, sometimes more. Fruits grooved down one side. Stone usually flattened.
Sect. 1 Prunus. Plums. – leaves convolute in the bud (i.e., each half of the leaf is rolled inwards). flowers stalked, solitary or in clusters of two or three. fruits bloomy. stones sculptured. confined to the old world.
P. cerasifera, P. cocomilia, P. consociiflora, P. domestica, P. salicina, P. simonii, P. spinosa.
sect. 2 Prunocerasus. American Plums. – Leaves usually conduplicate in bud as in the cherries (i.e., the two halves of the leaf are folded together lengthways like a sheet of notepaper). Flowers stalked, in clusters of three or more. Fruits as in sect, i, but the stones usually smooth.
P. alleghaniensis, P. americana, P. angustifolia, P. hortulana, P. maritima, P. nigra, P. orthosepala, P. subcordata.
sect. 3 Armeniaca. Apricots. – Leaves convolute in the bud. Flowers and fruits very short-stalked. Fruits velvety. This section is treated as a distinct subgenus by some authorities, or even as a separate genus – Armeniaca.
P. armeniaca, P. brigantina, P. mume, P. sibirica (P. dasycarpa is probably a hybrid between this group and sect. Prunus.)
Almonds and Peaches
Axillary buds three, the centre one vegetative, the laterals producing flowers. Terminal bud present. Leaves conduplicate in the bud. Flowers and fruits very short-stalked or sessile. Fruits downy (except in the nectarine), stones grooved or pitted. This subgenus divides into two groups, each of which is treated as a separate genus by some authorities – Persica, the peaches, with a fleshy fruit; and Amygdalus, the almonds, with a dry fruit.
P. argentea, P. davidiana, P. dulcis, P. kansuensis, P. mira (stone smooth), P. persica, P. tangutica, P. tenella, P. triloba.
Leaves conduplicate in the bud. Flowers in clusters, sometimes racemelike, or in corymbs. Fruits not grooved, usually without bloom, and with a smooth and not flattened, usually more or less globose, stone. The cherries fall into two main groups:
(a) Dwarf shrubs, having the axillary buds in threes, as in the almonds and peaches. This is the section Microcerasus, which in Ingram’s view should rank as a separate subgenus – Lithocerasus (Orn. Cherries, p. 78).
P. besseyi, P. glandulosa, P. humilis, P. incana, P. jacquemontii, P. microcarpa, P. prostrata, P. pumila.
(b) Trees or mostly large shrubs, with the buds solitary in each leaf-axil.
P. apetala, P. avium, P. campanulata, P. canescens, P. cerasus, P. concinna,
P. conradinae, P. dielsiana, P. emarginata, P. fruticosa, P. incisa, P. litigiosa, P. mahaleb, P. maximowiczii, P. nipponica, P. pensylvanica, P. pilosiuscula, P. rufa, P. sargentii, P. serrula, P. serrulata, P. speciosa, P. subhirtella, P. tomentosa.
Leaves conduplicate in bud. Flowers in racemes which are terminal on leafy branchlets.
P. cornuta, P. cuthbertii, P. grayana, P. padus, P. serotina, P. ssiori, P. virginiana. (P. maackii is anomalous in having short axillary racemes, borne on the previous season’s wood, but is usually placed here.)
Evergreen. Flowers in racemes like those of the bird cherries, but produced from the axils of the still persisting leaves of the previous year.
Prunus ilicifolia, P. laurocerasus, P. lusitanica.
The cultivation of Prunus generally is somewhat varied owing to the wide variety of the species composing it. Generally they are very hardy; where they are not, the fact is noted. All the deciduous species enjoy full exposure to sunlight; it is on this more than anything else that the flower crop depends. They all thrive on loamy soil, and most of them, the plums especially, are at home on limestone formations.
Many of the species, or most, can be increased by cuttings. This method of propagation is well worth trying for those that are found to be shortlived when grafted or budded. The cuttings should be made of young wood getting firm, with a heel attached, and put in gentle heat. Peaches and almonds are usually grafted or budded on plum stocks because of the greater hardiness of the plum. The various cherries may be worked on P. avium, and the bird cherries on P. padus. The cherry laurels may be increased by cuttings.
The species and cultivars of Prunus do not in general need annual pruning, the main exceptions being P. glandulosa and, when grown against a wall, P. triloba. But the ornamental peaches and apricots will flower better and be more healthy if the plant is kept open by cutting back old wood to a suitable young growth and removing growths that are badly placed. This should be done after flowering. Grown as a hedge, P. cerasifera and its hybrid P. × cistena should be trimmed after flowering, and the leaders should be shortened each year until the desired height is attained. See also P. laurocerasus.
The ornamental members of the genus are susceptible to many of the diseases that attack their orchard relatives, and works on fruit-growing or the R.H.S. Dictionary of Gardening should be consulted for an account of these. The only disease that calls for preventive spraying is the Leaf Curl disease of peaches and almonds, caused by the fungus Taphrina deformans, which over-winters on the bud-scales and attacks the young leaves, which become red, thickened and contorted, and eventually die. The plants should be sprayed in the autumn before leaf-fall with Bordeaux mixture at the rate of 1⁄2 pint to two gallons and again in late winter before the buds expand. It is pointless to spray in spring or summer after the disease has been noticed, but the affected leaves should be picked off and burned. The witches’ broom disease – Taphrina cerasi – must be mentioned, as it is fairly common on some ornamental cherries, especially on P. subhirtella ‘Autumnalis’ and hybrids with P. subhirtella in their ancestry. The disease causes the tree to produce dense bunches of shoots, which are thicker than normal, come into leaf earlier, and bear no flowers. Once the disease has taken hold it is difficult to cure and the tree, apart from producing few flowers, becomes very unsightly. The witches’ brooms should be removed as soon as noticed, and burned. Spraying with Bordeaux mixture as the leaves unfold is said to check the disease, but badly affected trees are best removed.
From the Supplement (Vol. V)
The Manual of Japanese Flowering Cherries, published by The Flower Association of Japan in 1983, gives an account of all the native species and hybrids, and their cultivars, with detailed descriptions. The publication of this book, obviously the fruit of much devoted labour, is a welcome sign that, after several decades of rapid industrialisation and social change, the Japanese are now making a concerted effort to preserve what remains of their great floral inheritance. It is well illustrated with 194 colour photographs.