This is done by thinning out crowded branches. On the other hand, it may sometimes be necessary to induce lateral branching by cutting off the tips of the larger polelike branches.
Pruning pome fruits
Apple. One- or two-year-old trees are usually planted which may be single-stem whips or branched. They should be cut back to about 4 feet. If the one-year-old plant already has branches, it may be possible to select some of them for the "scaffold" branches.
These will be the main branches and, ideally, should be distributed equally around the main trunk and from 6 to 9 inches apart. Perhaps there will be insufficient suitable branches at the end of the first growing season, but the following year the growth will probably be such that enough branches will be available from which the remainder of the scaffold branches may be selected.
Very little additional pruning will be needed during the next five or six years or until the flowers are formed. One thing to watch out for, though, is a possible development of undesirable crotches.
Pear needs very much the same kind of pruning as Apple except that, because of its tendency to grow upright, the cuts when made should always be to an outward-pointing lateral or bud, or to one which when it grows will fill a gap in the branches.
Quince usually is trained in bush form to insure against the danger of losing the entire plant if attacked by borers. Pruning consists of removal of superfluous suckers and thinning out the top whenever the branches become too crowded.
Pruning stone fruits
Peach, Nectarine, Apricot. When one-year-old Peach trees are planted the usual method of pruning is to cut all lateral shoots to a single bud and shorten the leader to 24 inches. The following year the laterals should be shortened to induce branching. Subsequent pruning consists of cutting out some of the crowded branches to open up the centre of the tree to air and to sunshine. Flowers are produced on the shoots of the preceding year.
Cutting back some of these shoots is good practice, as this is one method of thinning the fruit. Nectarine is a fuzzless Peach and requires the same treatment. Apricot pruning is essentially the same as that of Peach except that fruits are produced on spurs as well as on the wood of the preceding year. Consequently, the spur growths are not cut off so long as they continue to bear.
Plum. There are three principal groups of Plums—European, Japanese, and hybrids. Plums are quite likely to over-bear, which may cause breakage, especially when named varieties are planted; consequently, the modified central leader system of training is preferred (see Apple).
Scaffold branches are selected as soon as possible. Meanwhile the leading shoot should be maintained until a sufficient number of scaffold branches are functioning or until the tree has reached the required height, when it is cut back to the first strong lateral. Weak shoots which are not pulling their weight should be removed annually. Pruning to remove shoots infected with black-knot fungus is commonly necessary.
Cherry. Sweet Cherries and the Japanese Flowering Cherries tend toward an upright habit of growth, which can be maintained by pruning. Some of the varieties seem to bunch their shoots instead of producing them at 6-inch intervals, which is a desideratum. I am inclined to think that it is a regular habit with some types of edible Cherries and the Japanese Flowering Cherries to produce the main branches within a comparatively small compass on the trunk.
Preventing the trees from producing their main branches in clusters can be done to best advantage when they are young. This is accomplished by pinching out most of the branches with thumb and finger when they are no more than an inch or two long. Once the scaffold branches are established little or no further pruning is needed beyond cutting out dead wood. Occasionally it may be necessary to cut back a branch that is developing too rapidly and to thin out crowded branches.
Sour Cherries have a bushy habit of growth. The scaffold branches should be selected as soon as possible. The lowermost branch should start at least 20 inches above the ground line. The leader is maintained until the tree has almost attained the desired height. Then it is headed back to the first strong lateral branch. From time to time, when other branches take the lead, they also are cut back to the nearest lateral and it may be desirable to cut the weaker of two crossing branches.
Blackberry when planted in the fall should be cut back to 6 inches. Blackberries need plenty of room, so set them 3 feet apart in rows 8 feet apart. During the second summer cut off at the ground line those canes which have fruited and cut back the remaining canes about one third. The following spring cut back the laterals about one third and the thin, spindling shoots to the ground line.
Boysenberry, Dewberry, Loganberry, and roungberry are trailing Blackberries which are not winter-hardy in the northeastern states. The fruit-bearing canes are tied to a trellis, but those which are to bear the following year are allowed to trail along the ground. When fruit has been gathered the canes which have produced it are cut away and those which were lying along the ground are tied in their place.
Blueberry. The High-bush Blueberry (Viburnum corymbosum), so far as I know, is the only kind that is extensively cultivated commercially. Often the named varieties have a tendency toward overbearing. This is not good, because coupled with it is the fact that the berries sometimes do not ripen properly. Furthermore, overbearing one year may result in lack of berries the following year.
The remedy is to cut off weak, twiggy shoots and to remove one or two of the oldest branches annually and possibly cut off some of the weaker of the fruit-bearing shoots. This is a case, as always, of using your own perceptions in deciding how much pruning is desirable, because some varieties are more prone to over-bearing. Also they may behave differently in bearing in different environments.
Red Raspberries are planted 5 by 5 feet apart, or when they are grown in a solid row, 3 feet apart in rows 7 feet apart. In the first system the stakes are set at planting time in the spring, while in the row system plants are set 3 feet apart and are tied to wires which are stretched along the row.
The pruning consists of removing, in the summer, the canes which have fruited. This will make room for the new shoots to grow which will provide the fruiting canes for the following year. In the spring the canes are cut back about one fourth before growth starts, and any weak or crowded shoots are cut off at the ground line.
Red Raspberries have a suckering habit which requires the use of a spade to keep them within bounds. The row should not be allowed to exceed 15 inches in width with the canes no closer together than 6 inches.
Blackcap Raspberry. Unlike the Red Raspberry, these do not produce any suckers. The new canes should be tipped when they are about 2 or 3 feet high, which causes them to branch. The lateral branches should be cut back the following spring to about 9 inches.
Purple Raspberry, a tremendously strong grower, is similar in growth habits to the Blackcap, but the top growth is not so hardy as that of either the Blackcap or Red Raspberry. Because of this strong growth, it is not adapted to small gardens. In this same category are the Trailing Blackberries, which are even more vigorous.
Currant. Red, White, and Black Currants act as alternate hosts to the destructive white-pine blister rust. Black Currants are seldom grown in this country, partly because they serve as the favourite alternate host to the blister rust and partly because the fruit does not appeal to American palates.
Pruning of Red and White Currants should be directed toward the maintenance of five or six branches not more than three or four years old. This is done in the spring by cutting out at the ground line, annually, branches four or more years old. When they are planted in rich soil it may be necessary to shorten or pinch out the tips of Red and White Currants about midsummer. Do not pinch out the tips of the Black Currant.
Gooseberries are also on the "black list," because they, too, are alternate hosts to the white-pine blister rust. Pruning involves cutting out branches four or more years old and those which grow so low that the fruit may be spattered with mud during heavy rains.
Fig is fairly hardy with winter protection in climates no more severe than that of Long Island, New York. Figs are produced in the axils of the leaves of one-year-old shoots. Fruits sometimes are developed toward the close of the year, and if they are protected from the winter, they may come through to ripen their fruit early the following year.
Pruning in cold areas is designed to develop a shrub like plant rather than a treelike one, so, when plants are starting in the spring, tips are cut back, which stimulates adventitious buds to grow. The following year the tips of shoots are again cut off to further promote young shoots. In succeeding years crowded branches may be thinned out.
Attempting to grow figs in severe climates is questionable. The amount of work required to protect them over the winter is out of proportion to the value of the crop. Success is more certain when the bushes are espaliered against a wall which radiates heat and thus helps to ripen the young shoots.
This form of pruning is not commonly done nowadays. It consists of the removal, in the spring, of a cylinder of bark from a shoot of the preceding season. The depth of the cylinder varies from 1/10 to 1/16 inch. It depends for its effectiveness upon the fact that, in dicotyledonous plants, the course of the moisture absorbed by the roots from the soil with minerals dissolved in it is upward through the outer layer of the sapwood to the leaves. There it is combined with the help of chlorophyll, sunshine, and carbon dioxide to form starch and sugar, which are carried downward through the phloem (inner bark).
Ringing thus puts a roadblock on the translocation of elaborated food toward the roots. It is done sometimes to bring about early fruiting and sometimes to obtain material for making cuttings which because of the concentration of food are more likely to root. It is believed by some that, applied to Grapes, it increases the sugar contained in the berries and improves the flavour of the crop. This practice should be done with great care to avoid the possibility of permanent injury to the plant. There are some who prefer to use half cylinders by making the cuts about 2 inches apart on opposite sides of the branch.
Thinning fruit is a form of pruning which is important to amateurs as well as commercial growers. In a good year when there are no late frosts to change the picture and it is not so rainy that the bees are kept home, there are usually more fruits set than the tree can take care of. Nature ordinarily takes a hand in this case by what is known as the "June drop"; however, this may not be sufficient to remedy the situation. Thinning may be done by chemicals applied at blossom time (check with your county agricultural agent) or mechanically by removal of the surplus fruit in June.
Before actually picking off any of the fruits, the branches should be shaken to dislodge any insecurely attached ones and any that are infested with insects. Enough apples and pears should be removed so that those remaining are spaced 6 or 8 inches apart, peaches 4 to 7 inches, plums 3 to 4.
Among the benefits conferred by thinning the fruit are the following: the danger of breakage of branches due to the weight of fruit is lessened; it may help to prevent the tendency to become an alternate bearer; in the case of the stone fruits, the proportion of flesh to the inedible pit is higher; it helps to decrease brown-rot disease by promoting better air circulation; it makes it easier to achieve better coverage with pesticidal sprays or dust.
If you are interested in taking prizes for Grapes at the County Fair, thinning the number of berries in the bunch is desirable. Scissors with rounded points are used. Usually thinning is spread over a period of several weeks, starting when the Grapes are about the size of small peas, the idea being to leave each Grape ample room to grow without being crowded by its nearest neighbour.