According to the growth and fruiting habits of American plums, the tree shape suitable for American plums mainly includes natural joy shape and "V" shape with many main branches.
The natural happiness of many main branches accords with the natural growth of trees, with light pruning, easy shaping, good ventilation and light transmission, quick forming, early fruiting and high yield.
V-shaped trees are suitable for close planting with good ventilation and light transmission, but it is difficult to shape and master the opening angle of branches. If the angle is too large, it is easy to draw strong bars on the back and disrupt the tree shape.
The trunk height of young American plum trees is 40 ~ 50 cm. Among the new branches sprouting under cuttings, 3 ~ 4 new branches with healthy growth and suitable direction are selected as main branches. When it grows to about 60 cm, pick (cut) the tender part with the apex of 10 cm to promote growth and branching. The extended branches leave outer buds, and the rest branches are lightly cut or slowly put according to the space size and density. When competing branches appear on the back, they should be thinned as soon as possible, and at the same time, the buds that may germinate the clustered branches on the back should be removed. When pruning in winter, the extension branches of each main branch should be shortened by about 50 cm, and 2 ~ 3 lateral branches should be selected on each main branch, and the rest branches should control excessive vegetative growth and promote flowering and fruiting.
After the plum tree began to bear fruit, the tree shape basically formed. Pay attention to control strength when pruning. Extending branches at the periphery, and selecting weak branches to take the lead; Lateral branch extension branch, with anticline side or dorsal branch as the head; Deal with competitive branches in time; Flat and oblique branches on backbone branches at all levels, as well as branches with medium growth, should be placed as slowly as possible, and then retracted or thinned according to the situation after flowering and fruiting.
After entering the full fruit stage, the flower quantity and yield increased greatly. The extension branches at all levels can leave short sections of 40 ~ 50 cm, and the weak branches can be used as heads to reduce the peripheral tension. When competitive branches are found, they should be thinned or controlled in time. For the main branches with too small opening angle, methods such as bracing and pulling can be used to continue to open the angle to about 60 degrees to alleviate their growth. For auxiliary branches with strong growth, methods such as supporting branches and pulling branches can be used to open corners, slow down growth and promote flowering and fruiting. For weak branches that bear fruit for many years, some strong branches can be properly thinned or cut off, and for moderate branches with inner cavities, light pruning can be used to promote flowering. When they enter the late stage of full fruit, they should be refreshed and rejuvenated in time to prolong the life of full fruit.
The main task of plum pruning in summer is to open big branches and pick new shoots. The opening time of the main branch is from mid-May to mid-June. The wood of Prunus americana is brittle, and it opens at other times, which is easy to cause branches to diverge. The opening angle is about 60 degrees. Too small and easy to be strong, poor ventilation and light transmission, low yield. Too large an angle can increase the yield, but the branches are easy to break when there are many fruits.
When the new shoot length is about 60 cm in summer, the tender part of the shoot tip is about 10 cm, which can control the overgrown vegetative growth, promote branching and form flower buds.