Leaning or Slanting Trunk Style

by Siggy Franz

Since I have been asked to write about the above style, it is only natural to start by identifying what is meant by leaning or slanting trunk style and it is here that I ran into my first problem. The classification of Bonsai according to trunk angle started with Yuji Yoshimura in the early 50s. He suggested that trunks which departed up to 20° from the vertical should be referred to as informal upright, and those between 20° and 45° were slanting trunks. More than 45° from the vertical should be called semi-cascade ( he did not mention that the branches of this style had to reach the level of the upper pot rim). The late Mr Yuji Yoshimura was a very dear old gentleman with profound knowledge and highly respected throughout the bonsai world. It was certainly not his intention that growers style their trees by degrees, but he tried to create some standard terminology by which the basic style of a tree could be described and the listener had some idea what was meant. I would not be surprised if the whole idea of classification did not come about in order to please the western mind.

Unfortunately many people in the West have deduced a system of "style by numbers" and in Koreshoff's book we even find the advice that slanting trunks lean between 11°(!) and 45°. These "measurements" are taken from the tip of the apex to the centre of the nebari. I don't think one should take any of the above too seriously since this classification was never intended to analyse each tree in detail and pigeon-hole it.

Starting with a straight trunk tree two things are important in order to retain visual stability when the trunk leans to one side. The roots should portray the strength necessary to support the tree at its angle. This means that they should appear suppressed and buttressed on the side of the lean and more exposed and horizontally pulling on the opposite side. The degree of this one sided rootage increases with the angle of the lean. This somewhat one sided rootage may enable us to make use of a tree that would not look good when planted more upright.

leaning-bonsai-fig1Figure 1

The second requirement to retain visual stability is the direction and length of the branches. If the lean is only slight, the branches should have more or less the same angle to the horizontal on both sides of the trunk. I can think of several large examples of Norfolk pines in Hermanus, maybe 30m tall, straight as a ruler and growing at an unstable angle, but their branches are horizontal all around.

leaning-bonsai-fig2Figure 2

If a straight trunk tree has its branches at the same angle to the trunk the tree will look unnatural as if it has just been pushed sideways.

leaning-bonsai-fig3Figure 3

As the lean increases, the branches opposite the lean would have to be longer in order to balance the visual weight of the trunk. Being longer and therefore heavier they usually grow at a more downward angle than the shorter branches on the other side. This happens in nature because the branch growing above the leaning trunk gets more sun and rain. As the foliage on this branch increases, sap circulation is increased which leads to further vigorous growth. In addition the extra weight of rainwater or snow will lower this branch even more.

leaning-bonsai-fig4Figure 4

leaning-bonsai-fig5Figure 5

Stability can also be achieved by one or two small secondary trees at the base of the trunk or some carved jin section opposite the lean. Sometimes a very low feature branch is used to add visual weight.

leaning-bonsai-fig6Figure 6

leaning-bonsai-fig7Figure 7

A tree with a slanting trunk and a very high first branch can form a large empty space under the trunk. This can be made interesting with the addition of a rock or even a landscape.

leaning-bonsai-fig8Figure 8

This visual stability is most important. Without it the tree will never look good. It may be useful to consider how and why trees should grow at an unnatural angle. In high and exposed rocky mountains trees can grow at any weird angle ( even cascades ) since their angle depends on predominant wind pressure at different times of the year. Other factors like the size of the available soil pockets or snow and/or falling rocks at a particular growing spot will shape the tree. This is the great attraction of yamadori (collected trees).

In more gentle surroundings the trees at the edge of dense forests invariably grow outwards towards the light and the sun. Similarly trees growing at the edge of lakes or rivers tend to grow at an angle over the water because of greater humidity due to evaporation and light reflected from the water into the branches above.

leaning-bonsai-fig9Figure 9

Then we have trees which once grew more upright but were dislodged due to storms, rockfalls, wash-aways or falling nearby trees. This last example occurs more often than one thinks. We have seen a number of once straight trees growing at a precarious angle in indigenous forests near Hogsback and Stormsriver. They were brought down by falling trees but caught at some angle by others, their tremendous rootball half torn out of the ground. When this happened a long time ago, one can see that those roots which had still retained contact with the soil grew thicker and stronger, while others which were hanging in the air simply rotted away. Over time a one sided rootball grew which was able to support the one sided weight of the slanting trunk. Available light and sun adjusted the branches after some years.

Most trees growing at an angle for some reason or another will tend to revert back towards upright, forming an upwards curve. When a tree has grown clear of a competing one or clear of a building etc. it follows its natural trend to grow straight up ( see Fig. 6). Strangely enough this is not the case with Norfolk Island pines. Once set at an angle (I assume up to a point) they grow like a ruler.

Describing how nature produces slanting trunks brings me to trees which according to their trunk angle should be called leaning, yet are "called by a different name".

Firstly there is the windswept group. This leaning trunk may be straight or curved, often the bark on the windward side has been sandblasted away by the wind or has dried out exposing some jin.

leaning-bonsai-fig10Figure 10

leaning-bonsai-fig11Figure 11

leaning-bonsai-fig12Figure 12

leaning-bonsai-fig13Figure 13

If the angle is caused by persistent wind pressure, the trunk is inclined to curve away from the wind, thus forming a curve opposite to that described above.

It is of course the branches and foliage which give windswept trees their typical looks. And since these are the dominant visual features, they are usually referred to as windswept rather than slanting style. If one wants to be pedantic, one could of course use both terms.

Similar reasoning applies to weeping species. A weeping willow at the edge of a lake with a curved but leaning trunk and the branches hanging long over the water will always be referred to as weeping style, because the weeping branches are the dominant visual feature.

leaning-bonsai-fig14Figure 14

The same applies to root-over-rock style and of course to literati. Descriptions like weeping, windswept, root-over-rock and literati really say something about the character of a bonsai, while the classification according to trunk angle only does that, namely describe the angle of the trunk. This does no more than give an approximate visual image of the kind of tree one is talking about, no more. One should certainly not design to fit into a known style. Just walk in nature and try to assign a style to each tree you see.

leaning-bonsai-fig15Figure 15

leaning-bonsai-fig16Figure 16

This is the reason why the Chinese resist any kind of classification. For them the feeling of ancient wisdom, successful struggle for survival and a strong suggestive feel of what the tree had to endure is important. They only admire what we might call the aura of the bonsai / penjing. Their trees generally are such that they defy western classification. Figs. 15 and 16 show some example of what a "Chinese slanting style" might look like.