Detailed Explanation of Walnut Tree Pruning Techniques and Methods

  Walnuts mostly bear fruit on the terminal buds of branches. Except to encourage branching, walnut branches generally should not be headed back, otherwise fruiting will be affected. Overcrowded branches and dead branches can be thinned out. Weak branches and branches in sparse areas of the inner canopy can be heavily headed back or cut back to encourage new growth, achieving the effect of three-dimensional fruiting. For mature trees, especially old walnut trees, thinning and cut-back pruning of overcrowded branches should be strengthened. As the branch order of walnuts increases, branch vigor weakens accordingly, fruiting capacity declines, and the dieback rate increases markedly. Through yearly pruning, the branch order should be reduced as much as possible, keeping the tree's branches within the range of 3~4 orders, and preferably not exceeding 5 orders.

  Improved-variety walnuts use the heading-back pruning method more often, which is also the main aspect that differs from the pruning method for seedling walnuts. In seedling walnuts, female flower buds are mostly borne on the top 1~2 buds of the fruiting mother branch, so pruning mostly uses thinning and long-cane leaving, and rarely uses heading back; whereas in improved-variety walnuts, more than 85% of the lateral buds on 1-year-old vigorous branches can form female flower buds and bloom and bear fruit. Heading back can prevent the fruiting zone from moving outward, plump up the base, and also serve to thin flowers and increase the fruit-setting rate. Different degrees of heading back produce rather large differences in pruning response.

  Heavy heading back: For 1-year-old vigorous branches, cut off about 2/3 of the branch length. Generally, 1~2 vigorous branches can sprout below the cut, while the less plump buds lower down either do not sprout or sprout into medium and short branches, and some die immediately after sprouting, especially on excessive water shoots, where this response is even more obvious.

  Light heading back: Cut off about 1/3 of the branch length. Below the cut, 1~3 relatively vigorous branches sprout, and many medium and short branches sprout beneath them. If the branch is thick and strong, with sufficient nutrition, vigorous shoot growth, and a high fruit-setting rate, it can bear good fruit. If too much length is left, with many buds retained and many branches produced, there will also be more fruit, but the growth vigor is dispersed, making the branch prone to weakening, and the small branches at the base die off, soon becoming bare, causing the fruiting zone to move outward.

  Medium heading back: Leave about 1/2 of the branch. The response lies between heavy heading back and light heading back. Below the cut, 2~3 vigorous branches can develop, with strong growth but a low fruit-setting rate, and 3~4 moderately vigorous branches can sprout beneath them, fruiting well, with a high fruit-setting rate and plump kernels. In the training of young trees, medium heading back can be used when pruning the tips of extension branches at all levels, which helps expand the crown and develop fruiting branch groups.