Key Technical Points for Scion Preparation in Conventional Walnut Propagation

  1. Source of scions - Select superior varieties as mother trees for scion collection and establish a scion orchard. Cutting scions from a scion orchard ensures variety purity. Scion mother trees should be of pure variety, grow vigorously, and be free of pests and diseases. After collecting scions, they must be labeled to prevent mixing, because walnut varieties are relatively difficult to distinguish from branches and tree bodies, and once mixed, they will bring great trouble to future production. Sometimes scions are also cut from production orchards, and attention must likewise be paid to the issue of variety purity; at the same time, the amount of scions collected should be smaller, so as not to weaken the tree body or cause a relatively large reduction in yield. It is best to cut scions from trees that have already borne fruit, as this makes it easier to distinguish varieties. However, in current production, because the demand for nursery stock is large, the practice of cutting scions from young trees is quite common, which often brings hidden dangers of variety mixing and is also unfavorable to the growth of young trees.

  A professional scion orchard requires a clear source of varieties, preferably ones that have already fruited and have no major pests or diseases. As needed, mother trees in the scion plot can be used to collect scions 3 times a year. For scions used for spring grafting before bud break, all one-year-old branches can be heavily cut back, leaving 3~5 buds, to promote new branch growth. After cutting scions, be careful to promptly apply paint to the cut surfaces to protect the mother plant and prevent excessive bleeding, which can weaken the tree body. Collect the second time from the end of May to mid-June, with the amount collected being 60% of the new shoots of the current year; the remaining branches should be left until the following spring for collection during spring grafting. Collect the third time in late July, taking scions from the new shoots that sprouted after the second collection. The scion orchard should have strengthened fertilizer and water management to promote branch growth and fullness and improve scion quality.

  2. Collection of scions for branch grafting. For scions, choose one-year-old branches about 1 m long and 1~1.5 cm thick, requiring full development and a relatively small pith. Cut them off leaving 3~5 buds at the base, then grade them by thickness and length, bundle them 50 pieces per bundle, hang variety labels on them, and keep proper records. Scions collected in winter should be placed in a cellar and buried with wet sand; the scions should be placed loosely so that the wet sand fully contacts the scions. Scions collected in spring should be grafted as early as possible.

  3. Collection of scions for bud grafting. From the end of May to mid-June, select lignified current-year vegetative branches with high bud maturity, plump and full; use them as soon as they are collected. Immediately after cutting the scions, remove the leaves, leaving petioles about 2 cm long; they must not be too short, otherwise the wound will be too large. Bundle the trimmed scions (20 or 30 per bundle), wrap them with a wet cloth, mark the variety, and graft as soon as possible.

  4. Storage and transport of scions. Scions for branch grafting can be transported in early spring or late autumn, when the temperature is relatively low but the scions will not be frozen. During transport, attention must be paid to moisture retention. When storing scions, they can be buried in wet sand in a cellar, with good results. For the method, refer to the stratification treatment of seeds. Note that every scion must contact the wet sand, so stored bundles of scions must not be too large; it is best to bury them loosely so they fully contact the wet sand.

  Scions for bud grafting are best collected and used locally as soon as possible, avoiding long-distance transport. During transport, wrap them well with plastic film, put some wet sawdust inside, and do not seal them tightly; allow proper ventilation. For short-term storage, they can be hung in a water well 10 cm from the water surface, or placed in a cold storage facility, kept above 0°C, and not allowed to freeze. The grafting survival rate of bud-grafting scions decreases as storage time lengthens; generally, the storage period should not exceed 5 days. When grafting in the field, wrap the scions well with a wet cloth and place them in a cool place, avoiding direct sunlight.

  5. Scion treatment. Scions used for branch grafting generally need to be wax-sealed, which can prevent water loss and improve the grafting survival rate. 3~5 days before grafting, take out the scions stored in winter, cut them into 15~20 cm lengths with 3~4 plump buds, with the cut 1~2 cm from the first bud. The branch grown from the first bud in the future will be the best, so special attention must be paid to the quality of the first bud. The wax-sealing method is as follows: put commercially available paraffin (adding a small amount of beeswax gives better results) into a container (an aluminum pot or iron pot is acceptable), heat it over fire to melt the wax, insert a thermometer into the liquid wax, and control the temperature of the liquid wax at 120~140°C. After the wax liquid melts, put the scions into the liquid wax and dip them quickly, shake off the excess wax liquid on the surface, so that the entire surface of the scion is coated with a thin, even, transparent wax film. For a small number of scions, use tongs or chopsticks to hold the scions and dip them one by one; for a large number of scions, use a strainer basket, and when using a strainer basket, 10~20 scions can be treated at one time; do not use too many, to prevent lowering the wax temperature. The specific operation method is: place 10~20 scions in the strainer basket, quickly immerse them in the wax liquid, immediately take the strainer basket out, give it a little shake so that part of the wax liquid falls back into the pot, then immediately swing it with slight force onto the ground covered with plastic sheeting, so that the scions scatter in all directions rather than piling up in one place, which helps heat dissipation and prevents the scions from sticking together. Note that the wax temperature must not be too high or too low. If the temperature is too high, it is easy to scald the scions to death; at this time, remove the container from the heat source to cool it down. If the temperature is too low, the wax layer on the scions will be too thick and prone to cracking and falling off; when the wax temperature drops, it needs to be reheated. Nowadays, using an induction cooker for heating allows convenient temperature control. A small amount of water can also be added to the container and used to heat indirectly, controlling the temperature of the liquid wax within the range of 90~100°C; this can protect the scions from being scalded, but because the temperature is lower, the wax-sealing effect is not as good as direct heating over fire. Freshly wax-sealed scions should not be piled together; they should be spread out to promote rapid heat loss, so as to protect the scions from being scalded. If they are not to be grafted immediately after wax sealing, the scions can be wrapped with a wet cloth and placed in a refrigerator or temporarily stored buried in wet soil in a cellar.

  After bud-grafting scions are collected, if they are to be transported long distances, grafting wax is also needed to seal the cut surfaces to reduce water loss. Those collected and used on the spot do not need wax sealing and can simply be wrapped with a wet cloth.