Wherever the Domestica and Japanese plums can be grown, the native plums are not destined to become popular; but many of the natives are much hardier than others, and are therefore adapted to regions in which the Domestica and Japanese are not safe. Others of them are well adapted to the middle and southern states. The Domestica and Japanese plums are considerably hardier than peaches, but not so hardy as the apple. The northern limit of their general cultivation is the southern peninsula of Michigan, central and southern Ontario, central New York, and central New England.
Plums thrive on a great variety of soils, but they do better, as a rule, on those that are rather heavy and have a considerable content of clay. In fact, many of the varieties will thrive on clay as hard as that in which pears will grow. On the other hand, they often thrive well in light, and even almost sandy soils.
The trees are set when they are two and three years from the bud. It is preferable to have plum trees on stocks of the same species, but it is not always possible to secure them at the nurseries. In the South, plums are worked mostly on peach roots, and these make excellent trees where the climate is not too severe, and especially on the lighter lands on which they are planted in the South. In the North the larger part of the plum stocks are grown on the Myrobalan plum roots. This Myrobalan is an Old World species of plum, of smaller growth than the Domestica. This stock, therefore, tends to dwarf the tree, and it is also likely to throw up sprouts from the roots.
Plum trees are set 12 to 18 feet apart. Many growers like to set them 8 feet apart in rows, and have the rows from 16 to 20 feet apart.
Plums are pruned much the same as apples and pears. That is, the top is thinned out from year to year, and all superfluous branches and broken or diseased wood are removed. If the soil is very strong and the trees are close together, it may be well to head them in a little each year, especially those varieties which grow very strong and robust.
Pests and diseases.
There are four leading difficulties in the growing of plums—leaf-blight, fruit-rot, black-knot, and curculio.
The leaf-blight usually appears about midsummer, the leaves becoming spotted and dropping off. The remedy is to spray thoroughly with bordeaux mixture, beginning soon after the fruits have set, and before the trouble begins to show.
The fruit-rot may be prevented by the same means—that is, by spraying with bordeaux mixture. It is usually best to begin just after the fruits are well set. A very important consideration in the checking of this disease is to thin the fruit so that it does not hang in clusters. If one fruit touches another, the rot spreads from fruit to fruit in spite of the spraying. Some varieties, as Lombard and Abundance, are specially susceptible to this injury.
The black-knot is best kept in check by cutting out the knots whenever they can be seen, and burning them. As soon as the leaves drop, the orchard should be gone over and all knots taken out. Orchards that are thoroughly sprayed with bordeaux mixture for the leaf-blight and fruit-rot fungus are less liable to attacks of black-knot.