First Step: Pruning for Improvement
When it comes to large trees that need to be replaced with better varieties, the first step is to design the tree shape based on its specific conditions. Big branches should be arranged in a structured way, and any unnecessary ones at the base should be removed. The remaining branches should be cut to stimulate latent buds to sprout, and according to the tree's growth needs, permanent extension buds and temporary spare buds should be selected carefully.
It is best to prune the tree before the start of the growing season, as this minimizes sap bleeding and promotes strong germination of latent buds while helping the wounds heal faster. The number of cuts should not be excessive. For medium-sized trees, the first layer should be above the main branch, with the central leader pruned to about 60 cm, and the first layer’s main branches pruned to around 50 cm. For tall trees, the second layer should be above the main branch, with the central leader pruned to 30 cm, the second layer’s main branches to 20 cm, and the first layer’s main branches to 50 cm. All pruning cuts should be flattened and covered with a protective film to prevent cracking and speed up healing.
After pruning, it is essential to select the right bud to grow. That means choosing the central bud on the upper left side of each branch, leaving a secondary branch to extend backward, and a lateral spare bud. On the main branches of the first layer, leave an extension shoot at the tip, and one on each side. If there are no existing branches, it is important to leave some empty buds. Any unwanted buds should be removed promptly to reduce nutrient consumption. The selected extension buds and spare buds should be topped to about 20 cm for grafting purposes.
Second Step: Grafting
Choose high-quality walnut varieties suitable for your region and perform grafting in the year following the pruning or in June of the next year. The grafting method can vary: experienced individuals may use block budding, while others can opt for I-shaped budding. A blade made from two pieces of wood is ideal for making a rectangular block (3 cm wide and 2 cm thick), which helps create a double-edged knife. This ensures a clean, even cut and proper alignment of the graft. Regardless of the method used, the graft should be connected once, and the interface should be aligned in the direction the graft needs to grow. After grafting, wrap the area tightly with transparent tape wider than the interface to ensure a secure seal, which significantly increases survival rates.
After grafting, proper care is crucial. If grafting is done in July, it is important to prevent the buds from sprouting prematurely. After grafting, only the original branches should be removed, and other branches and leaves should remain untouched. Do not cut the scion or remove the bandage until spring when the buds begin to grow. For grafts done in June of the following year, focus on controlling the growth to ensure the graft has enough development to survive the winter. After grafting, leave three compound leaves to cut off the scion. After 10 days, check the graft’s survival, remove the compound leaves, and eliminate other buds to concentrate nutrients and promote bud growth. When the graft reaches 10 cm, cut the scion and release the bandage to encourage rapid growth. Once the shoots reach late August, control their height and strengthen the lower parts. Also, although walnuts have strong healing abilities, the newly grafted leaves are heavier than those of other fruit trees. Therefore, it is advisable to tie the top of the graft with sticks to prevent wind damage.
Third Step: Positioning and Shaping
By the third year of the update process, the new grafts are usually about 80 cm long, and the cultivation technique for Weibei dryland walnuts begins. It is important to position and shape the tree correctly to help restore the canopy quickly. The method involves leaving healthy, upright extension branches in the center and shortening them to about 80 cm. Promote the second or third layer of main branches and pull other branches into horizontal positions as supporting branches. Shorten the second-layer branches to 60 cm to encourage side branches. Do not cut or release the lateral branches. If an extension branch is damaged, replace it with a nearby spare branch. Leave other temporary spare branches to produce early results. In summer, you can adjust the azimuth angle of the main branches using techniques like bending, pulling, or lowering.
In the following summer, continue adjusting the azimuth of the main side branches by selecting the second or third layer of the main branch on the central branch and thinning out the rest from the base. Gently release the extended branches of each layer and make a full-bud cut on the lateral branches to encourage branching. Remove temporary spare branches that do not affect the main branches and allow the rest to grow naturally. At this point, the basic structure of the new tree is complete. Over the next few years, continue adjusting angles, removing useless branches, and controlling back branches. All branches will eventually grow naturally, and temporary spare branches should be managed appropriately to avoid interfering with the main branches.
Field experience has shown that this three-step method not only renews old branches and improves the variety but also rationally modifies irregular tree shapes. For example, in areas like Gansu, this technique has enabled the first year of fruit production within three years and reached full yield in five or six years, doubling the original output. (Gansu Science and Technology News - Ma Haisheng)
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