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Sometimes bonsai or potentsai can have poor quality nebari/surface roots or poor quality lower trunks. This can take the form of too few overly-thick roots, a combination of thick and thin roots or one-sided nebari which can spoil an otherwise excellent bonsai. This problem can be relatively easily and quickly rectified by using layering techniques as described in the Advance Techniques articles on Layering. Layering produces numerous roots that emanate radially from all around the trunk which is ideal for quality nebari.
When using this technique, repot the bonsai into a deeper pot or the ground and leave it unpruned to encourage vigorous growth. New roots can be developed higher up the trunk by either air-layering or if only just a little higher than the existing nebari, the ring-bark or tourniquet air-layering method can be used and the tree planted deeper into the ground or pot so the layering is below the level of the soil.
When the new rootsystem has become well established after one or two seasons, the old rootsystem and trunk base can be removed. A by-product of the tourniquet method is that the base of the trunk above the tourniquet swells resulting in excellent trunk flare. An alternative to using wire as a tourniquet is to plant the tree in the ground through a hole in a ceramic tile.(For more details on this technique, please see Part Two of this article) As the trunk slowly thickens, the hole in the tile bites into the bark and cambium layers (as a wire tourniquet does) and as the trunk swells above the surface of the tile, new roots are produced. Eventually, all roots below the tile can be removed and the tree is left with excellent root and trunk flare, and radially spreading roots which are flat-bottomed making them ideal for bonsai cultivation.
This technique is carried out in early Spring at repotting time if any root disturbance is necessary in order to apply the toruniquet. However it can be carried out at any time of the year, if the tourniquet can be applied and the soil level increased without disturbance of the rootsystem.
These Larix kaempferi/ Japanese Larch were purchased as bare-root stock and typically each had a very poor nebari with thick downward growing roots only.
The first picture shows one of the trees temporarily planted into a pot before being planted into the ground.
After 2 years growing in the ground the Larch were lifted; here you can (just) see the green wire tourniquet, the old root system below it and the new root system above it.