The primary task of plastic work is to maintain a balanced tree potential and maintain the subordinate relationship between branches at all levels in the crown. That is, the trunk is thicker than the main branch, and the main branch is thicker than the side branch; Among the lateral branches at all levels, the three-year branch should be stronger than the two-year branch, and the two-year branch should be stronger than the one-year branch. If the branches at all levels in the crown grow unevenly, the nutrient distribution will be unbalanced, which is bound to be that the stronger the strong, the weaker the weak; The weak branches will decline early, and the strong branches will grow excessively, resulting in disorder of subordinate relationship and deflection of trees, which will also affect flowering and fruiting. In order to maintain a balanced tree potential and a good tree shape, we should mainly do the following work:

1. Change branch angle

Changing the growth angle of branches can adjust the growth direction of branches. Too strong branches mostly grow upright, and the incident angle is relatively small. We can change their incident angles by pruning, thus weakening their growth potential. For this reason, some large branches can be corrected by means of wooden stick support and pulling rope, and the new branches can be distributed reasonably in the crown by correctly selecting the remaining cutting buds (cutting off the first side buds).

For example, for branches that grow too vigorously, cut buds can be left inside the branches (Figure 13A) to make new lateral branches grow inward. In the crown, the growth potential of inward-growing branches will gradually weaken. When cutting off the weak branches, the buds should be kept outside the branches (Figure 13B), so that the new branches will grow outside. Because this growth direction conforms to the natural growth trend of flowers and trees, the growth potential can be changed from weak to strong.

Figure 13 Choosing different cutting directions can change the growth direction of branches.

A. When the axillary buds are left, the new branches grow inward and the growth potential is weakened. B. when the external axillary buds are left, the branches grow outward and the growth potential is enhanced.

According to the above principle, the distribution of lateral branches in the crown can also be adjusted by selecting incisions in different directions, so as to supplement the branches at the vacant positions and prevent the generation of parallel branches and cross branches.

2. Keep the normal spacing between trees.

In order to make the street trees and shade trees in the garden close together as soon as possible, the spacing between plants is sometimes designed to be smaller when planting seedlings. With the continuous growth of tree age, the lateral branches between two trees often cross and interfere with each other. If it is a mixed forest, some slow-growing tree species will stop growing under the inhibition of big trees. At this time, it is necessary not only to prune the overlapping large lateral branches among the big trees, but also to weed out the poorly growing small trees under the forest and increase the row spacing between trees, so as to provide a place for tourists to take a walk in the shade.

3. Strong branches and strong shears, weak branches and weak shears

Re-pruning the overgrown branches can promote several lateral buds to germinate at the same time, thus dispersing nutrients and weakening the growth potential of the original branches. The weak branches should be lightly cut, which can promote the germination of cutting buds and keep the old branches growing forward, so as to keep the growth balance of branches in different parts of the crown.

For some big branches that grow too long, don't trim too much at one time, but cut them short several times to keep the same length as the branches at the same level. Otherwise, it will stimulate a large number of hidden buds to germinate because of one-time pruning, grow many useless long branches and consume a lot of nutrition.

4. Replace the central leadership branch or the central main branch.

In the case of weak tree potential, most of the lateral branches in the middle or lower part of the crown are rare and there are few leaves. At this time, the flowers and fruits are only planted at the top of the crown, and the number is also small, which reduces the ornamental value.

The best way to solve the above problems is to saw off the central main branch or central main branch of tree species, so as to promote the germination of lateral buds or hidden buds in the middle and lower part of the crown and form a complete crown. This practice is called "head change". Changing the head can not only prevent the crown from being hollow, but also depress the flowering and fruiting parts, change the crown appearance and make it develop around.

5. Handling of auxiliary branches

Except for trunk, main branch, central main branch and big side branch more than three years old, other side branches are called auxiliary branches. If these lateral branches are not too dense or interfere with each other, they should be kept as much as possible in order to make full use of the cavity in the crown to increase the leaf area. Because, the more leaves, the more assimilated nutrients produced by photosynthesis. Only when carbohydrates are quite sufficient can a large number of flower buds form and blossom and bear fruit, and the growth rate of trees will also accelerate.

6. Handling of competing branches

When two large lateral branches emerge from the mother branch at the same time and grow together in parallel, they must compete with each other. At this time, because the local nutrition is scattered, their growth potential is bound to be very weak. In plastic surgery, we should choose a normal growing branch and cut off another competing branch to maintain local balance.