Horticultural News
       
        M. Elena Garcia,  Horticulturist

Grafting and Propagation Agreements

At this time of the I often receive requests for grafting techniques either to remedy rodent damage or to top-work trees to a newer cultivar.  The following is  a review of grafting techniques, not only as means to repair the tree but also as means to replace an existing cultivar would be an appropriate subject for this newsletter.  The information on  grafting techniques to repair damaged trees was published on the March 98 issue of this newsletter.  If you need this information let me know and I will send it to you. 

Basic grafting terms
Grafting:   The art of joining parts of plants together in such a manner that they will unite and continue to grow as one plant.
Scion: The twig or bud that will become the top part of the new plant. It is what is grated unto the stock.
Stock: The root, trunk, or branch upon which the scion is inserted. It may be a young seedling plant or a large tree
Cambium: A thin layer of living cells between the bark and the wood from which bark and wood tissues are formed. It is the source of all girth growth in woody plants, woody stems. As the cambium cells divide bark is produced to the outside and wood towards the inside. During the healing of wounds, such as those incurred during grafting, the cambium produces callus cells which will join the scion and the stock. Eventually, theses callus cells differentiate, forming the vascular connections between the stock and scion.
Graft union: The place where the scion and stock grow together.

Requirements for a successful grafting operation.

1. The stock and the scion must be compatible. In other words, they must be capable of uniting. Usually, the more closely related the plants the better the chance of the graft taking. For example, apple to apple is much more successful than apple to pear
   
2. The cambial region of the scion must be placed in close proximity with the cambium of the stock.
   
3. The cut surfaces must be held together tightly by wrapping, nailing, wedging, or some similar method.
   
4. Rapid healing of the graft union is necessary so that the scion may be supplied with water and nutrients from the stock by the time the buds start to open.
   
5. The grafting operation must be done when the stock and scion are in the proper physiological stages. Usually, the scion buds need to be dormant whereas the stock needs be capable of producing callus tissue for the healing process to occur. For apples, dormant scion wood is collected during the winter and kept inactive by storing at low temperatures. The stock may be dormant or active depending on the grafting method used.
   
6. Immediately after the grafting operation is completed, all cut surfaces must be protected from desiccation. The graft union may be covered with tape, grafting wax, or with moist materials covered with some type of grafting frame .
   
7. Proper care must be given to the grafts for a period of time after grafting. Care must be taken that shoots coming from the stock below the graft do not choke out the desired growth from the scion. It is recommended that the scion be supported to prevent breakage due to the wind or the weight of the fruit.
   
8. The knife needs to be very sharp. A grafting knife needs to be razor-sharp to insure success.  A utility knife can be used instead of a grafting knife.  Advantages of a utility knife over a grafting knife include cost and no sharpening.