Plum, Prunus species - pruning
WHY The flowers of most varieties are borne on spurs. The pruning of the Plums and Prunes is thus performed to favor spur production. The training is essentially the same as that suggested for Apple trees, except that the trees should be trained to a vase or funnel shape, not with a semi-pyramidal or central axis. This type of shape will result in having the center of the tree well covered with stubby spur-development which will produce fruit year after year.
WHEN Pruning is done during the dormant period, preferably in late winter or early spring.
HOW After the young trees have been cut to form a short trunk from 18 to 24 inches with a scaffold of 3 to 5 laterals with good crotch angles, very little pruning should be done other than the removal of dead, rubbing and crossing branches, until the tree begins to bear fruit. Wood growth is much less in mature trees. Pruning then consists of keeping the vase shape of the tree, removing dead or damaged branches, shortening or cutting back the current season's growth to keep the young twigs in a vigorous growing condition and to thinning out spurs to prevent overbearing. If the trees are becoming taller than desired, there is no harm in heading back, usually cutting back to vigorous side branches. Many advise allowing the long slender branches of some varieties to grow, permitting them to remain until they have produced a crop, which they will do in the second season. When these slender whips bend too low and possibly interfere with the tree, they are cut back to the crown from which they are replaced by new slender shoots. Some advise clipping the new growth of the top of the tree 2/3 to 3/4 of its length, until the tree is about 10 years old and has the desired form. New branches, they suggest, should be removed entirely if they are of no benefit to the form of the tree. The ideal shape is to have the branches about 1 foot from each other, thus making for easier picking and permitting light to penetrate. Since the spurs are in the center of the tree, they should be well protected; it is best to harvest the fruit from a ladder instead of standing on limbs within the tree.
Native plums make a good barrier fence if they're sheared tightly. Treat them like hawthorns and crab apples. Plant them two or three feet apart.
If necessary, prune this right after blooming, and shear it as needed during the summer to keep it in shape. Most of these don't bear any fruit.
Some trees grow twiggy naturally, and certain apple varieties such as Jonathan, as well as many varieties of cherries, plums, peaches and apricots, need additional thinning of their bearing wood to let in sunshine to ripen the fruit.
Trees bear their fruit either on the limbs or on short, stubby spurs between the branches. Pears, plums and cherries grow mostly on spurs, peaches grow on one-year-old limb growth, and most varieties of apples are produced both on spurs and on limbs.
Because spur-type fruit trees make less limb growth, they need less pruning. Since this means considerably less labor for the orchardist, scientists have worked on breeding trees that produce mostly on spurs, and there are now many varieties of this type of fruit tree available.
When too many fruit spurs develop along a branch, cut out some of them to encourage bigger and better fruits on the rest. After a few years of experience, you'll be able to judge about how many spurs are right for the tree. Each spur will usually produce for several years, but then you should cut it off to allow a replacement to grow. You'll be able to spot the older spurs by their aging appearance.
Pruning Simplified Book: Prune plums carefully to help them produce well and to allow the sun to ripen the fruit before the first frost hits. Due to their straggly habit of growth, plums are almost always grown to an open center.
Follow the usual directions for pruning when planting. One-year-old whips, from four to seven feet tall, are the best choice if you're planting European and American plums, and two-year-old, slightly branched trees are preferable if you are planting the Japaneses varieties. Cut back the whips about a third, to a fat bud, and cut off any side branches until you've removed from a third to a half of the total wood area.
European plums need very little pruning and an occasional thinning of the older wood is usually all that is necessary. Most American plums and hybrids of American plums need only moderate pruning to keep them bearing well; however, some varieties, including some of the cherry-plum hybrids, grow very long branches that hang on the ground and should be shortened. Prune the tree to keep it in balance. Many plum roots sucker badly, so periodically cut off the small trees growing from the tree's roots unless you keep the area under the tree well-mowed.
If your plum trees have a habit of bearing a large crop every other year, you may want to thin out some of the fruit to limit the large crop, to increase fruit size, and to encourage annual bearing. Trees producing large plums especially benefit from thinning. Pick off the extra fruits when they are still tiny in early summer so that the plums are five inches apart.
Some varieties of plums, especially the European kinds, are quite susceptible to a disease called black knot. Thick excrescences form along the twigs and are especially noticeable in winter. As there is no spray available to control this problem, pruning is necessary. Attack it with your pruning shears whenever the infection appears during the summer. Disinfect the tools as you work, and burn or dispose of the diseased parts promptly to prevent any spreading of the trouble. It is also a good idea to remove any infected wild plums or cherries growing nearby.