Detailed Explanation of Key Techniques for Summer Pruning of Walnut Trees

  Summer pruning generally refers to pruning during the growing season, and its main contents include bud removal, pinching, branch thinning, girdling, branch bending, and summer shoot tipping. Its role is to regulate the contradiction between growth and fruiting, improve tree light conditions, cultivate robust fruiting branch groups, and increase the fruit-setting rate. Because summer pruning is carried out during the growing season, its effect is more direct, faster, and more obvious than winter pruning, and it is especially beneficial for flower bud formation, so summer pruning must be taken seriously. Each item is introduced below.

Pictured: walnut

  1. Bud removal and sprout elimination: After budbreak and in the early stage of new shoot growth, remove buds that sprout side by side and new shoots on the back of main branches to save nutrients and improve light conditions. If removed by hand at the initial sprouting stage, they will not sprout again; if they are allowed to grow larger and then cut off, they will still sprout again.

  2. Pinching: During the rapid growth period of new shoots, remove the tender tip 5~10 cm at the top of the new shoot. During the training period of young trees, when the extending new shoots of the main and lateral branches reach 50 cm, pinch them to promote secondary shoot growth and accelerate crown formation. For upright branches or water sprouts inside the crown that can be used but need to be controlled, early pinching can change them from upright growth to oblique growth. Pinching flat and oblique branches when they reach 30 cm is beneficial for flower formation and lowers the node position of flower buds. In September, pinch new shoots that have not stopped growing so that they stop growing, promote fullness, and help young trees overwinter.

  3. Branch thinning: During the growth period of new shoots, remove useless upright vigorous branches and excessively dense branches inside the crown to save nutrients and improve light inside the crown.

  4. Branch bending during the growing season: For growing branches with a small branching angle and upright growth, bend the branches or use spreaders to open the angle, increase the angle of main branches, lateral branches, and other branches, change upright branches into flat and oblique branches, improve light conditions inside the crown, and favor flower bud differentiation.

  5. Summer shoot tipping: During the slow growth period of new shoots, shorten upright branches by cutting off the non-lignified part to control their growth and promote branching. In short, summer pruning of walnut is very important, and generally 3 times are carried out. The first time is before the rapid growth of new shoots, carrying out bud removal, sprout elimination, and removal of excessively dense branches and competing branches. The second time is during the rapid growth period, selecting upright branches with suitable positions and pinching them at about 20 cm to promote secondary shoots. Pinch flat and oblique branches at 30 cm to favor flower bud formation and lower the node position of flower buds. The third time is in June to July, removing excessively dense branches and water sprouts to save nutrients. Pinch vigorous secondary shoots again to promote branch maturity and flower formation.