Pruning Methods for Different Types of Branches on Walnut Trees

  1. Pruning of skeletal branches: Promptly retract crossing skeletal branches. For overly weak skeletal branches, retract them to well-grown lateral branches growing obliquely upward, so as to raise the angle of the extension branch. For trees reaching a height of about 3.5 m, promptly drop the head.

  2. Training and renewal of bearing branch groups: The training of bearing branch groups in walnut is an important measure for increasing yield, stabilizing tree vigor, extending the full-bearing years, preventing the bearing part from moving outward, and preventing premature senescence. The methods for training bearing branch groups include: growing long first then retracting, cutting back first then growing long, and transforming auxiliary branches.

  (1) Growing long first then retracting: That is, 1-year-old vigorous branches are left unpruned and bent down; generally they can produce more than 10 new shoots with bearing branches, and in the second year they are retracted to train them into bearing branch groups. The distribution of branch groups should be even in density, dense but not crowded, with large, medium, and small ones matched together. Generally, in the inner part of the main branch, there should be one large branch group about every 1 m, one medium branch group about every 60 cm, and one small branch group about every 40 cm. At the same time, growing long, thinning, cutting back, and retracting should be combined to continuously adjust size and vigor, maintaining good ventilation and light penetration within the canopy, so that branch groups grow robustly and bear many fruits.

  (2) Cutting back first then growing long: When the space is relatively large and a large bearing branch group is to be trained, first moderately cut back a 1-year-old vigorous branch, and in the second year thin out 1 to 2 vigorous branches at the front end while letting the other branches grow long, thereby training a bearing branch group. Alternatively, in early June, pinch the new shoots to promote branching, then retract again during winter pruning, and a bearing branch group can be trained in 1 year.

  (3) Transformation of auxiliary branches: For auxiliary branches that have space, after their auxiliary role is completed, they can be trained into large branch groups by retraction. Generally, the method of growing long first then retracting is used, and the position of the branch group is best on an obliquely upward branch. On the upper side of the branch, only small branch groups should be kept, and no branch groups should be kept on the underside. The spacing between branch groups should be controlled at about 60 to 80 cm.

  The renewal and rejuvenation pruning of bearing branch groups has as its core the adjustment of the contradiction between vegetative growth and reproductive growth within the branch group, and the regulation of the ratio of vegetative branches to bearing branches, so that branch development, flower bud differentiation, flowering, and fruit set remain in a dynamic, virtuous cycle. When pruning, consider the position of the; weakly branches should be promptly retracted, and vigorous branches should be appropriately deferred, so as to maintain the bearing branch group in a state of robust growth.

  3. Pruning of bearing branch groups: After bearing branch groups are formed, some medium and long bearing mother branches should be cut back to varying degrees each year to control the fruit load, prevent alternate bearing, and promptly thin out overly dense branches, slender weak branches, and some male flower branches. Upright-growing bearing branch groups should not be left too tall when pruned; few branches should be retained, only 3 to 5, and they should be controlled within a certain range to prevent excessive expansion from affecting the growth of the main and lateral branches. For obliquely growing branch groups, if there is relatively large space, more branches may be appropriately retained to make full use of the space. Promptly use retraction and thinning methods, removing the lower and keeping the upper, removing the weak and keeping the vigorous, and renewing bearing mother branches so that they always remain robust in growth and prevent the inner part from becoming bare and the bearing part from moving outward.

  4. Handling of branches on the underside: After walnut trees bear heavily, the growth of branches on the upper side weakens, while the growth of branches on the underside becomes vigorous, forming the phenomenon of the main and lateral branch heads being "pulled backward" to seize the head. If the original branch head has a small opening angle, the original head can be cut off and replaced by the underside branch. If the original branch head has a suitable or relatively large opening angle, the underside branch should be promptly retracted or thinned out.

  5. Handling of water sprouts: In the early bearing stage, water sprouts are generally not retained, so as to avoid disrupting the tree shape. In the full-bearing stage, when there is space, appropriately select and retain them, and promptly adopt methods such as cutting back and pinching to transform them into branch groups.

  6. Handling of secondary branches: Improved walnut varieties easily form secondary branches. Because secondary branches sprout late, grow vigorously, and are not plump, with a long section at the base lacking buds and forming a bare zone, they should be promptly handled. When there is space, remove the weak and keep the vigorous, and pinch in June to July to control vigorous growth and promote the formation of bearing mother branches. When there is no space, promptly thin them out.