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.
After removal of the old root system and the trunk below including the tourniquet. Here it is possible to see how the new rootsystem is shallow and consists of many lateral roots. It is also possible to see the increase in trunk diameter of the trees after only 2 years growing in the ground.
Dave Paris read this article and applied it to a pomegranate. A year later and he has kindly sent some images of the great success he has had.
'The tree is a Dwarf Pomegranate; Punica granatum cv. "Nana Emperor" and was procured from Bill Valavanis at International Bonsai in Rochester, NY, USA. It traces its lineage back to cuttings taken from a tree owned by the Emperor of Japan (hence the "Nana Emperor" cultivar name). The trunk on the tree in the images is between 5/8" and 3/4". '
'The tourniquet was applied approx. 1/2" above the existing, weak nebari and was created from 2mm anodized aluminum wire, tightened sufficiently to cut into the bark. The tree is currently potted in an 8" nursery "bulb" pan filled with coarse bonsai soil and roughly 20% (by volume) sphagnum peat to retain moisture so the new roots don't dry out as the top of the bonsai soil dries.'
Here is a further example of using a tourniquet, this time to create a new nebari on a field maple/Acer campestre;
This tree was planted in the ground as a young sapling and has been grown on for 3 to 4 years. Unfortunately, it has a very poor trunkbase/nebari so before being planted back into the ground, a wire tourniquet is applied in order that a new nebari can develop over the next few years.
After two more years growing in the ground, I lifted the tree and found that there were plenty of new roots growing just above the layering point/tourniquet. I pruned the old rootsystem very hard to promote stronger growth in the new roots.
This is the appearance of the same tree 3 years after the tourniquet was applied. As can be seen, the new surface roots have numerous fine roots to help support the health of the tree and the old root sytem has barely healed or developed since it was pruned back a year ago. This means that the tree is being supported solely by the new roots. The entire base of the trunk (below the tourniquet point) can now be removed.
The old root system has now been removed using a saw. The trunkbase of this tree is around 2"-3"/5-7cm in diameter. The wound at the base of the trunk is given a thin layer of vaseline but in all honesty, it is not necessary to try and 'protect' or 'seal' the exposed wood.
PART TWO OF THIS ARTICLE Creating New Nebari on Bonsai Part Two Developing a Multi-Trunk Bonsai on a Tile or Board