Techniques in grafting
BEFORE describing the techniques of grafting, some concepts and terms (terminology) have to be explained for complete understanding of the process and solutions to any problems that may arise.

Both grafting and budding are techniques that connect two pieces of different plants together. Usually they are performed to take advantage of the root system of plants that are well adapted to certain regions, and the cultivation of plants not adapted to these locations. One of the best advantages of grafting and budding is that they break the juvenility of plants, so they start producing much earlier, besides maintaining the quality of the propagated material. Here, juvenility is the capacity to develop only vegetative growth. It can be said of the difficulty of engaging into reproductive growth, and consequently the production of flowers and fruits.

In either grafting or budding, only plants that belong to the same botanical family can be propagated by these techniques. Therefore, mangoes are to be grafted on mangoes, avocados are to be grafted on avocados, and citrus are to be budded on citrus.

Grafting can be defined as the ability to connect two living parts of a plant together, resulting in growth of a new plant. Budding is the same ability, the only difference being using a smaller living plant part, a bud.

The grafted plant is composed of scion and rootstock. The scion is the plant material that is intended to be propagated. It is usually a piece of detached shoot containing several dormant buds. The scion is grafted on the rootstock, which is originally grown from seed, but can also be a cutting that has been rooted.
The vascular cambium is the tissue (group of cells) that surrounds the stems of the plant. It is located between the bark (phloem), also called stem skin, and the wood (xylem).
This is the tissue that is really responsible for the success of grafting or budding. To have successful grafting or budding, the vascular cambium of both scion and rootstock must be in contact with each other. This tissue has the ability of cell division and forming new cells that will connect the graft forming the new plant.
In order to have successful grafting or budding it is important to observe the following points:

•    Choose mature graft with dormant buds. For budding, select buds that are at the middle portion of the branch. Avoid buds from the terminal portion of the branches.
•    Either the grafts or the buds have to show no sign of disease or insect.
•    The scion and the rootstock must have the same diameter, or as close as possible.
•    The scion on the rootstock must have the same position that it had before harvesting. Buds should be budded upside up.
•    There should be a clean and sharp cut on the scion and on the rootstock.
•    After the cuts, both surfaces should be put in contact as soon as possible to avoid dehydration of the surfaces.
•    There should be enough pressure on the wrapping tape to ensure perfect contact between the scion and rootstock, and avoid rain or irrigation water from wetting the graft union.
•    After grafting, the graft should be protected against dehydration. It should be covered with a transparent plastic bag cap.
•    The grafted plant should be allowed to grow for some time under a cool and moist place.

A good practice for ensuring success in grafting and budding is to have the grafting knife as sharp as possible for a sharp and clean cut. There are several types of knife and once they are sharp all of them will work in the same way. Also, the tools used during grafting or budding should be as clean as possible. They should be cleaned with 50% bleach solution and then rinsed with plenty of clean water.

The grafts and bud stick should also be cleaned, using the same procedures for cleaning the seeds. (A quick 1 to 2 minutes wash with a 3% bleach solution (1½ cup of bleach in 10 liter of water) will eliminate possible contamination of the grafts and buds. Immediately after washing, rinse the grafts and bud sticks with plenty of clean water, and leave them to dry in a clean, shaded, and cool place. A clean towel can be used to wipe off the excess water. The grafts should be placed in a clean bucket and covered with a clean, damp towel).

Commonly, a greater number of grafts are harvested than can be grafted on the same day. These grafts can be placed in a cool moist place, away from direct sunlight and grafted next day.  If grafts are to be shipped out or left to be grafted several days later, dip their ends in melted candle wax, cover them with moist newspaper and put into a plastic bag. Wrap the bag with more moist newspaper and keep it in a cool place. Sometimes damp sawdust can be used instead of newspaper. Avoid the harvesting of grafting material at times of high temperature and low humidity, such as from 11 am to 3 pm, as this can result in dehydrated material due to water stress.

Types of Budding and Grafting
There are several kinds of grafting and budding that can be used. The most common methods are:

Splice Grafting. Usually this type of grafting is used for herbaceous stems but it has been used successfully for semi-herbaceous or semi-hard wood plants such as mango, avocado, guavas, etc.
It consists of making a diagonal cut 2.5 to 3.5 cm long on the rootstock (Fig. 1) and on the scion (Fig. 2), placing both cut surfaces of the scion and rootstock in contact with each other and tying them together (Fig. 3). A plastic bag is placed over the graft to avoid dehydration (Fig. 4).

Figure 1: Remove the top of the rootstock at about 25 cm high and make a diagonal cut on the rootstock.

Figure 2: Diagonal cut made on the scion. Observe that the cambial tissue on both scion and rootstock must be in contact with each other. The picture above shows the position of the cambial tissue.

Figure 3: Place both cut sides together and wrap with the grafting tape.

Figure 4: After the graft is made, a plastic bag is placed over it to avoid dehydration of the scion.

Split Grafting, also called Wedge Grafting, is very similar to the previous method; however it is used on woody stems. Diagonal cuts 2 to 3 cm long are made on both sides of the scion (Fig. 5). These cuts must be symmetrical to fit perfectly in the cut in the rootstock and increase chances of success. The picture below shows that after the cuts the scion has an arrow shape.

Figure 5:    In the rootstock, a vertical cut 3 to 4 cm long is made, splitting it into two similar halves.

Next, the scion is inserted into the rootstock, tied with the grafting tape, and covered with the plastic bag (Fig. 6).

Figure 7: Scion is inserted into rootstock.
Below are the phases for split graft method (Fig. 8).

Figure 8: Sequence for Split Grafting.
In both methods above, always keep in mind that the Cambial Tissue of both scion and rootstock must be facing each other. The grafting will fail if these tissues are not put in contact.
As would be expected, most of the time a slight difference in diameter between the scion and the rootstock exists. In this way, to ensure success in the propagation method, at least, the cambial tissue on one of the sides of both scion and rootstock must coincide with each other (Fig. 9). To ensure that the cambial tissue of both scion and rootstock will be facing each other, just match their skins. The picture below (Fig. 19) shows the procedure for grafting scion and rootstock with different diameters.

Figure 9: Scion and rootstock with
different diameters must have at least
one of the sides matched.

Side-Veneer Grafting: This type of grafting (Fig. 10) was very popular at one time. It is used when there is a need for grafting more than one variety on the same rootstock or for the propagation of conifers and dwarf, compact potted plants. This method starts with a vertical cut, 2 to 3 cm long, half way in the stem of the rootstock. The scion receives diagonal cuts on both sides and is inserted into the cut made in the rootstock. They are tied together with the grafting tape and a plastic bag is placed over the scion. The top of the rootstock is cut off to avoid apical dominance. Because the grafting tape does not seal the entire union between the scion and the rootstock, watering should be made directly to the roots of the rootstock to avoid water entering the graft union.

Figure 10: Sequence for Side-Veneer Grafting

Sometime there may be a need to replace the scion of a mature tree. This method of replacement is usually called top-working. Either the splice or split grafting methods may be used for top-working. In this case, the plants are severely pruned at the trunk and the dormant buds grown into new branches. When these newly formed branches are still small, the grafting is performed on them. The procedures for top-working a plant are the same as described for splice or split grafting, only that the rootstocks are the new branches.

Next week we will discuss Budding Techniques.