Pruning and Training to a Central Leader
Figure 4.3. Response of trees to different heading heights: (A) the cut is too low; (B) the cut is at the proper height of 20 inches; and (C) the cut is too high.
The purpose of pruning a young tree is to control its shape by developing a strong, well-balanced framework of scaffold branches. Unwanted branches should be removed or cut back early to avoid the necessity of large cuts in later years. Currently, the preferred method of pruning and training nontrellised trees is the central leader system.
Pruning should be done in late winter. Winter pruning of apple trees consists of removing undesirable limbs and tipping terminals to encourage branching. Summer training is most beneficial if done in early June and early August.
First Growing Season
Figure 4.3 (B) shows the proper height, 30 inches, at which to cut back the tree at planting. Heading back the tree to this height will bring the top and roots back into balance and cause buds just below the cut to grow and form scaffold branches.
Cutting lower, 24 inches (A) will result in excessive vegetative growth. Cutting too high, 36 inches (C) will result in weak growth in the top of the tree as well as in lower areas.
After a few weeks, trees that are headed may appear as in Figure 4.4A. The shoots are vigorous and upright growing with very narrow crotch angles. To prevent this, you need to force the new shoots to a more horizontal growth pattern. When 2 to 3 inches of growth have occurred, position wooden spring-type clothespins between the main trunk or branch and the new succulent growth (4.4B). The clothespins will force the new growth outward and upward and form the strong crotch angles needed to support the fruit load in years to come. Allow the most vigorous upright branch to remain growing straight up—this will become the central leader. You should plan to keep approximately four to six of the developing shoots with the goal of having them separated equally around the trunk and arranged vertically within a 4- to 10-inch distance. Looking downward on the tree the arrangement would appear as in Figure 4.5.
Figure 4.4. Natural tree growth (A); placement of clothespins (B); and tree response at end of the growing season (C).
Figure 4.5. View looking down on an apple or pear tree and effects of spreading the tree limbs.
It is important that the limbs are spread when they are young. If a limb is not spread as in the picture above, a bark inclusion can develop. This occurs when the bark of the trunk and the branch have been pressed together. This structure weakens the branch and serves as an entry point for pathogens. The wide-angled branch on the right, however, allows for growth and expansion of both the trunk and the branch and produces a much stronger branch that can withstand future heavy crop loads.
One Year Old
A number of branches should have developed after the first growing season; if they were clothes pinned, they should have good crotch angles.
The objective now is to develop a strong central leader and framework of two to three sets of scaffold branches. Remove any broken limbs or limbs growing vertically. Head the central leader about one-third the length of the shoot that grew the first year. Several shoots should develop just below the heading cut. If the first set of scaffolds is vigorous and begins to grow too upright they should be spread through the use of wooden spreaders, weights, or string. Tie or spread the limbs down to a 45- to 60-degree angle.
Second Growing Season
During the second growing season, develop a second layer of scaffolds 24 to 36 inches above the scaffolds you established the year before.
Be sure to clothespin the second level to develop wide crotch angles. Remove any undesirable shoots that are too vigorous or in competition with the central leader during the growing season.
Two Years Old
Limb spreaders can aid in bringing about earlier fruit production, improved tree shape, strong crotch angles, and improved fruit color. Spreaders can be either short pieces of wood with sharpened nails driven into each end or sharpened metal rods.
Always spread the tree before pruning, which consists of entirely removing undesirable upright limbs and reducing the length of new shoot growth by one-quarter. Limbs should not be spread below a 60-degree angle from the main trunk. Limbs spread wider tend to produce vigorous suckers along the top of the branch and might have reduced terminal growth. The spreaders should remain in place for 1 to 2 years until the branch "stiffens up."
Figure 4.6 is an illustration of what the tree might look like after a couple of years. The objective is to try to leave only four to six main scaffold branches spaced around the tree. A second set of branches above the first is then developed the following year. Always make sure that the ends of the scaffold branches are below the end of the central leader after they have been pruned back.
Figure 4.6. An apple or pear tree trained to a central leader system after three growing seasons.
At maturity the overall appearance of the tree should be a pyramid with the largest and longest branches in the lowest and first set of scaffolds followed by 2 to 3 additional sets that are progressively smaller in diameter and shorter in length.
Three to Four Years Old
Continue to head back the new terminal growth by one-quarter each year and remove any upright limbs.
Any broken or diseased limbs also should be removed. Always maintain the central leader as the highest point on the tree. The ends of the primary and secondary scaffolds should be kept below the top of the tree. Prune the trees every year in late winter (February or March). Keep the leader dominant by shortening competing branches. Remove branches that form narrow crotch angles. Remove weak, twiggy growth.
Once the trees begin to bear fruit and no later than when they reach their fifth winter, discontinue heading back the new terminals. Pruning for the rest of the life of the tree will be done to maintain the conical structure.
Remove vigorous upright or downward-growing shoots. A good image to guide your pruning is to try to create two-dimensional scaffold branches. This means the branches will have a single terminal point and will spread out in a triangle back into the center of the tree but will not have any shoots growing up or down (Figure 4.7). Try to retain only shoots that are horizontal. Periodically thin out the branching structure to allow adequate light to penetrate the interior and lower portions of the tree.
Maintaining a three-dimensional Christmas tree form and a two-dimensional branch form
Always maintain the central leader as the highest point on the tree. The ends of the primary and secondary scaffolds should be kept below the top of the tree. Prune the trees every year in late winter (February or March).
TitlePruning and Training to a Central Leader
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