Japanese Plum and hardy hybrids
Deciduous, Edible fruit, Trees
Like their cherry, peach, and apricot relatives, these are stone fruits belonging to the genus Prunus, which is the name you'll find their flowering cousins listed under. For crosses involving plums, apricots, and peaches, see Plum Hybrids.
Three categories of edible plums and prunes are grown in the West: European, Japanese, and hardy. All bloom in late winter or early spring; fruit ripens at some point from May into September, depending on variety and climate.
The two most widely grown groups are European (Prunus x domestica) and Japanese (P. salicina). 'Damson' plum, which is sometimes considered a separate species, is probably a type of European plum (P. x domestica insititia); 'Damson' interbreeds freely with other European plums.
Prunes are European plum varieties with a high sugar content that makes it possible to sun-dry the fruit without it fermenting.
In the dry-summer West, plums are subject to far fewer problems than peaches or apples.
Dormant-season sprays combining horticultural oil with lime sulfur or fixed copper will control the fungal disease brown rot and various insect pests, including scale.Japanese plum
Japanese plums bloom earlier (and so are more susceptible to frost damage) than European plums, and produce fruit in many colors, both inside and out. Skin may be yellow, red, purple, green, blue, or almost black; flesh may be yellow, red, or green. Japanese plums are the largest and juiciest you can grow, with a pleasant blend of acid and sugar; they are mainly eaten fresh.
The trees grow 15-20 ft. tall, with slightly wider spread; but it’s easy to keep these trees 10-15 feet high. There are no truly dwarfing rootstocks for plums, and semidwarf trees are only slightly smaller than standards.
Most Japanese plums require 500 to 900 hours at 45’F/7’C or lower to produce fruit. Some are self-fruitful, but others need cross-pollination to produce good crops. Japanese varieties bear very heavily, producing much small fruit. If the entire crop were allowed to ripen, its weight might damage the tree’ so thin fruits to 4’6 in. apart as soon as they are large enough to be seen.
Where winters are severe, gardeners grow a complex group of hardy hybrids involving Japanese plum, several species of native American wild plums, and the native Western sand cherry (P. besseyi). Those with fruit near the size and quality of Japanese plums are sometimes called Japanese-American hybrids; those with smaller fruit closer in flavor to wild species are often called cherry-plum hybrids. Some of the hardy hybrids are trees; others grow as bushes to about 6 ft. high and at least as broad. The hardy hybrids originated in Canada, the Dakotas, and Minnesota and are exceptionally tolerant of cold and wind. Pollination of hardy hybrids is difficult; ask local nurseries about effective pollenizers.
Most Japanese plum trees are trained to a vase shape, with five or six main scaffold branches; fruiting laterals grow from these scaffolds. Where space is limited, trees can be trained in a more linear fashion (against a wall or fence, for example). Japanese varieties tend to make tremendous shoot growth, and rather severe pruning is necessary at all ages, regardless of training method. Many varieties produce excessive vertical growth; shorten these shoots to outside branchlets. If you grow hardy hybrids, prune them to renew unfruitful branches (on shrubby types, cut older shoots to the ground every few years) and to keep the plant’s center open.
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