Grafting

Grafting is the horticultural technique of binding together different parts of a plant so that they fuse into a unit that continues to live. It involves grafting a piece of one plant, a one or two year old branch, known as the 'scion', on to another plant usually of the same species, known as the 'stock'. The stock has the task of forming the roots and the lower trunk, and the scion will form the crown of the bonsai tree and the upper trunk. The fused plant pieces form a new plant although at the same time each retains its individuality. This can clearly be seen in the different types of shoots above and below the grafting point, the varying thicknesses of trunk, and very often the different patterns on the bark of the scion and stock. For the bonsai enthusiast grafting has a variety of uses-he can use the technique to cultivate his tree, then to improve it and again to maintain it. Trees whose roots have been damaged can be prevented from dying by grafting techniques; flowering trees can in the same way acquire flowers of different hues.

Plants that with other methods would be difficult or impossible to cultivate can be propagated by grafting. Experience has shown that white pines have grown much more quickly after a graft; that is, with the aid of a different root. That is why in Japan nearly all white pines are grafted on to black pines.

Another advantage of grafting is in producing a variety of plant strains, for although the plant will always correspond to the scion in appearance and color, seeds sown from the same plant may produce a great number of varieties.

However, there are also some disadvantages to grafting. The spot where the graft was carried out may not seal up attractively and unsightly shoots may start growing below the spot. The grafting technique itself needs skill and a certain amount of experience. The most important types of grafting as far as the bonsai-grower is concerned are lateral grafting, wedge grafting, crown or rind grafting, bud grafting and branch grafting. As a general rule plants are grafted at the beginning of spring before active growth has resumed. However, evergreen trees may also be grafted in late summer.

Lateral grafting

This is carried out in summer and is applied chiefly to evergreen broadleaves and conifers in order to cultivate new plants. The point where the graft is made should be as low down as possible on the lower trunk area so that it does not show up later on; if possible it should be hidden by earth. Cut the scion into a wedge about 3-5cm long, make a slanting incision of the same length on the trunk of the stock and insert the scion. Tie the scion to the stock with raffia and seal the grafting point with grafting wax (used for all types of graft), as this will stop the wound drying out and prevent water and pests from entering.

New growth from the scion the following year will tell you the graft has taken, at which point the stock should be cut away at an angle above the grafting point. If you do not want to use this method to create an entirely new tree, but perhaps only to insert a branch on a trunk that seems too long, then remember to keep one side shorter on the scion when you're shaping the end into a wedge. This shorter side should lie next to the trunk when you insert it into the stock so that the scion will stick out from the trunk with a natural curvature.

Crown, or rind, grafting and wedge grafting

Wedge grafting is attempted by bonsai experts only on fairly thin branches and trunks. If a trunk is more than 3cm thick the crown, or rind, grafting method is preferred. Crown, or rind, grafting enables you to form multiple trunks, or to create anew rather elderly trees with a sound root system. An inferior or damaged crown can be repaired by removing the crown of the tree from the stock and inserting new branches.

With crown grafting the scion has a much smaller diameter than the stock. First of all the stock has to be sawn through neatly and smoothed off with a knife-this helps the cut to heal better. Next make a vertical incision 2-5cm long down the side. Gently tap the two folds of bark until they come loose then insert the ready prepared, pre-cut scion. Using the same technique several scions can be arranged simultaneously round the trunk. Secure the grafted area with raffia to keep the scions firmly in place, then apply wax both here and to the cut surface of the stock.

Wedge grafting entails making a slit in the stock about 3cm deep parallel to the direction of growth of the trunk. Then insert at the side either one scion, 5-7cm long, previously sharpened into a wedge, or two scions one at each edge.

After securing with raffia, once again seal the graft with grafting wax. Wedge grafting enables you to insert new branches.

Bud grafting

With bud grafting, instead of a scion, only a small piece of bark with a well-formed heel is cut from the scion and inserted in the stock. This heel is the dormant bud lying at the join between the trunk and the leaf axil. This form of grafting is particularly good for inserting new branches.

The best time of year for bud grafting is summer, when the bark, complete with heel, will easily come away from the trunk. The bud should always be taken from the current year's growth area. Choose a fairly cool, rainy kind of day as this will help prevent the graft from drying out too quickly. Using a sharp grafting knife, make a T-shaped cut in the stock. Make the vertical cut first, about 2cm long, through to the xylem and not any deeper, then make the horizontal cut. Now loosen the bud from the scion, leaving a piece of bark about 1cm in diameter round the heel. If there is a leaf with the heel, remove it and only leave the leaf-stalk attached.

Using a knife, carefully peel back the bark of the T shape, open up the bark flaps and slide the heel in from above, using the leaf stalk as a lever if necessary. Then secure the graft with raffia or a rubber band, leaving the heel free. The graft will have taken once the leaf stalk has fallen off and a new branch has grown the following spring.

Bud grafting is particularly suited to fruit trees, such as apricot, cherry and peach, as well as roses. For the bonsai grower this technique is to be particularly recommended if he wants to turn a dioecious plant into a monoecious one, e.g. as with sea buckthorn and prunus-leaved holly. These plants form fruits only if both the male land female tree are present. By inserting a bud from a male, non fruit-bearing plant into a female, you can develop a tree that will fertilize itself and produce fruits.

Branch grafting

In this case the scion is not cut off straightaway; instead it is left attached to the parent plant for as long as it takes to fuse with the stock. This type of graft is suitable for all species of bonsai and is often carried out on the one plant, that is with both scion and stock part of the same plant.

Firstly cut away a strip of bark about 3cm long both from the stock and the scion, making sure that the cut sections match up well. Place them together and secure firmly with raffia or a rubber band, before sealing with grafting wax. The graft won't take till perhaps late autumn of the same year, assuming the graft was carried out in the spring. Only then should the scion be separated from the parent plant, the cut being made as close as possible to the stock to keep the swelling small. The wound will heal better and more quickly if wax is applied. You can prepare your tree for branch grafting by letting a branch grow near the spot where you want one and later on bending it down for grafting.

General advice on grafting

With conifers and evergreens the scions are removed from the parent plant directly before the grafting; with deciduous trees you must wait till growth has ceased in autumn and winter, before cutting the scions. Choose a frost-free day. Stick them in damp sand and keep in a cool place out of reach of frost.

Usually scion and stock are selected from the same species of plant to ensure the graft will take. Bonsai growers can carry out all the techniques described with a sharp knife-no other tool is necessary.

It is very important to carry out all grafts quickly and with the highest degree of cleanliness to stop any bacteria getting into the wound. That is why it is also important not to touch the wounds with your fingers.

After grafting stand your bonsai plant somewhere out of the wind where temperatures are constant-in a hotbed propagator or under a plastic film wrap. After the graft has taken the plant should gradually be acclimatized to normal environmental conditions. Remove the raffia after another year has passed.