Walnuts are light loving tree species, especially after entering the fruiting period, they require sufficient light. The tree shape can be divided into two types: an evacuation layered shape or a natural open center shape. Varieties with strong dryness and those with good site conditions adopt an evacuation layer shape, and the specific requirements and operation process can refer to apples. However, walnuts have the characteristics of late branching, vigorous tree body, and strong back branches. Therefore, in shaping, it is also necessary to grasp the requirements of high fixed trunk height (meters to 1.5 meters) and late fixed trunk period, as well as the distance between layers and the first secondary main branch (i.e. side branch) on the main branch from the central trunk, and not to choose the back branch as the secondary main branch. The crown should also be opened Varieties with weak dryness and poor site conditions can adopt a natural open-center tree shape, with 2-3 main branches selected for each plant, and 3-4 secondary main branches selected from each main branch to fill the space.
The pruning of young trees mainly involves dealing with some branches that interfere with the tree shape. Early fruiting walnuts are prone to producing large star secondary branches and male flower branches, and sometimes also prone to elongated branches. Secondary branches and elongated branches that need to be retained should be promptly picked or cut short, and cultivated into fruiting branches; The rest should be removed as soon as possible. For the back branches that are easy to dominate, those located on the first layer of main branches and auxiliary main branches should be removed from the base; Located on the main and secondary branches of the second and third layers, it is decided to keep the remaining branches according to their needs and growth strength. When the remaining back branches grow vigorously, they can be picked or retracted and transformed into branch groups.
Adults of large trees should promptly remove overly dense and drooping branches on the periphery, and prune and transform auxiliary branches that occupy a large space to improve the lighting conditions inside the tree crown. When the proportion of short branches and male flower branches in the tree crown increases, it indicates that the tree body has gradually weakened and should be updated and revitalized in a timely manner. For the fruiting branch group, weak branches can be removed, strong branches can be left behind, and the elongated branches that occur in the tree crown can be fully utilized for transformation and utilization to increase the proportion of strong and vigorous branches. When scorched shoots or large and medium-sized branches die, it indicates that the tree has become senescent. The backbone branches at all levels can be retracted and updated year by year, taking advantage of the long lifespan of hidden buds in walnuts to rebuild the ability of new crown restoration and fruiting.
Pruning during the dormant period of walnuts often results in bleeding due to poor healing of the cut, which can seriously affect the tree vigor. The optimal pruning period is after harvesting fruits in autumn and before the leaves turn yellow. In addition, it can also be pruned after germination.
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