Methods for Improving Inferior Varieties of Sichuan Pepper and Key Technical Points
To improve inferior varieties of Sichuan pepper, grafting is generally used. Grafting methods for Sichuan pepper include cleft grafting and sub-bark branch grafting, among others. Because the sub-bark branch grafting method is simple and tends to give good results, it is currently the method most used in production. In actual operation, the following points should be done well.
1. Timely Collection
Properly Store Scions. Starting from winter pruning, collection is best done around the time of Awakening of Insects. From the outer middle-upper part of the canopy of superior mother trees, select vigorous one-year-old branches with plump buds and no pests or diseases as scions. Scions of Sichuan pepper are not easy to store; if temperature and humidity are not properly controlled, they may sprout early or lose water and lose vigor. Therefore, collected scions should be promptly tied into small bundles and placed in a cellar or buried in soil in a shaded place. If conditions permit, storing them with full wax sealing gives especially good results.
2. Timely Grafting
Generally, grafting can be carried out in spring after the rootstock bark slips, but the best period is between Grain Rain and Beginning of Summer. This is because if grafting is too early, the temperature is unstable and the scions are easily harmed by late frost; if too late, rising temperatures are unfavorable for scion preservation and affect the survival rate.
3. Careful Grafting
1. Cutting the rootstock: For young trees, choose a flat surface about 5-10 cm above the ground and cut off the top; for mature trees, choose a flat surface from the lower part of each scaffold branch or vegetative branch and cut off the top. At the same time, remove all sprouts and prickles to facilitate binding and healing.
2. Cutting the scion: Select a scion section with 2-3 strong buds, cut off the prickles, and cut the lower end of the scion into a 3-5 cm “horse-ear-shaped” large slant. The knife should enter somewhat steeply, and after reaching the xylem, cut straight and level, achieving “long, thin, and flat.” Then cut a small slant of 0.5-1.0 cm at the lower end of the back side, sharpen the lower end of the scion into an “arrowhead shape,” and gently shave off the epidermis on both sides until the inner green bark is exposed. Then hold it in the mouth or place it in clean water to prevent contamination and water loss.
3. Cutting the rootstock and inserting the scion: Make a vertical cut in the flat upper part of the rootstock, reaching the xylem, with a length equivalent to the long cut surface of the scion. Then face the long cut surface of the scion toward the xylem and insert it along the cut until the white is slightly exposed, so that the cambium on both sides of the scion fits tightly against the inner bark of the rootstock.
4. Binding the graft union: Use a plastic film strip to wrap tightly and tie smoothly from bottom to top, so that it does not leak air or let in water. Then bury the rootstock and scion in wet soil within an earth mound to retain moisture and prevent freezing, which also helps keep the newly sprouted shoots from breaking easily.
4. Strengthening Post-Grafting Management
1. Promptly wipe off sprouts on the rootstock to prevent them from competing with the newly grafted branch for nutrients.
2. Loosen the binding material at the right time; generally loosen the binding 20 days after survival, and completely remove the binding material after about 30 days.
3. Tie the trunk and protect the branches to prevent wind breakage. Generally, when new shoots grow to 20-30 cm, promptly tie the trunk and protect the branches.
4. Strengthen water and fertilizer management. Apply quick-acting fertilizer as a top dressing and water to promote growth. However, in the later season (after August), water and fertilizer should be appropriately controlled; foliar spraying of potassium dihydrogen phosphate can be adopted to promote early lignification of new branches and prevent freezing damage in winter.