T budding or shield budding is a special grafting technique in which the scion piece is reduced to a single bud. As with other techniques of asexual propagation, the resulting plants are clones (genetically identical plants reproduced from one individual entirely by vegetative means). The plant being propagated (represented by the bud) is referred to as the scion, while the plant being grafted onto is referred to as the rootstock, or simply stock. A small branch with several buds suitable for T budding on it is often called a bud stick.
Successful T budding requires that the scion material have fully-formed, mature, dormant buds, and that the rootstock be in a condition of active growth such that the "bark is slipping". This means that the vascular cambium is actively growing, and the bark can be peeled easily from the stock piece with little damage. T budding can be performed on certain fruit trees (peaches, for example) in June using cold stored budsticks and field grown seedling rootstocks. Many deciduous trees are budded in late July or early August after the current seasons buds have developed fully and are dormant using field grown seedlings that have slipping bark.
|Bud sticks having plump, healthy buds are suitable scions. These budsticks should be on branches that exhibited good growth during the current season, rather than ones from the interior of trees that have slender stems and closely spaced, small buds. Thick water sprouts that grew very vigorously are often poor scions. Leaf blades are clipped from the budsticks, leaving the petiole intact. This leaves a convenient "handle" for holding the bud while it is cut from the budstick.|
|The bud and a small sliver of the wood underneath it are cut from the budstick using an upward slicing motion. The cut should begin about 1/2 to 3/4 inch below the bud, and should go deep enough into the wood so that when the cut is finished about 1/2 to 3/4 above the bud, the bark and a small sliver of wood are cut off. A perpendicular cut across the top of the upward cut will separate it from the bud stick.|
Budding knives should be kept very sharp, so that as little damage as possible is done to the bud. Dull knives strip and tear the wood, leaving cuts that do not heal properly. Buds must be cut from the bud stick just prior to grafting, otherwise they will dry out. Some grafters put the bud in their mouth for the time between when it is removed from the stick and when it is grafted in place, but this practice is not recommended. Speed in grafting is a more suitable solution.
Some grafters make a downward cut as the second cut to remove the bud from the budstick. This works well as long as it does not result in too much of the underlying wood being removed with the bud.|
A vertical cut is made on the stem of the root stock. The cut should be deep enough to insure that the bark will separate at the cambium.
|The "T is then crossed." That is, a perpendicular cut is made at the upper end of the vertical cut. In areas with heavy rainfall during the grafting season, or in species in which the rootstock is likely to "bleed" heavily, an upside down, or inverted T bud can be used to prevent water or sap from pooling in the graft.
|The bark is carefully slipped from the stem of the rootstock exposing a "pocket" into which the bud shield can be placed. Care should be taken not to tear the flaps of bark in the process of spreading them. |
If the bark does not slip easily, this indicates that the stock is not in active growth and the process should be conducted later when active growth has resumed.
An alternative method for budding which does not require the bark to slip is the technique of chip budding in which the bud is cut out with a "chip" of the underlying wood. This requires that a chip of corresponding size be cut out of the stock piece in order to align the cambia for proper graft healing.
|The bud shield is carefully slipped in between the bark flaps. The top of the bark strip on the bud shield is trimmed to fit tightly against the horizontal cut (the cross of the T) so that the bud fits within the "pocket" snuggly.
|The bark flaps are held tightly against the bud as they are wrapped with a budding rubber, grafting tape or other suitable closure. This closure must either breakdown by weathering (as budding rubbers do), or must be removed in 2 to 3 weeks after the union has healed. If the material does not break down, it will girdle the rootstock.|
After the union has healed, the upper part of the rootstock plant can be cut away to force the bud to grow (as would be the case for June budding). If the grafting is done in the late summer, the bud likely will need to overwinter prior to resuming growth. In this case, the upper portion of the rootstock is usually removed during the dormant season, either in late winter or early spring.