Understanding Proportion for Bonsai Development

Understanding Proportion for Bonsai Development

Bonsai Design Bonsai Growth Growing

Proper proportion holds the key to understanding the difference between many highly-regarded bonsai and their lesser brethren. More than the simple idea that a bonsai must be a perfect miniature tree, the higher goal - an aesthetically pleasing composition - can only be accomplished when all the elements harmonize in elegant proportion. The balance in the composition is the difference between a sublime bunjin tree and a rangy uninteresting stick. Proportion is the difference between a tree that pleases the eye and one that is merely mediocre.

Keeping things in proportion requires the thoughtful application of a few rules and guidelines. Assume that the trunk of a tree is an established size and shape; then build the branching and canopy to match. The size of that branching is not determined by the whim of the owner but by the relative proportions of the elements of the composition – the nebari, trunk, branches, and canopy. While an owner or bonsai artist may have a wide latitude in selecting the ultimate style of a tree based on rough stock, the proper size of the tree will be pre-determined largely by the trunk size, trunk taper, and trunk angle.

Trunk size 

When reading old bonsai books the rule of thumb is that the height of a bonsai should be typically 6-12 times the diameter of the trunk – a trunk with a 3-inch diameter (above the nebari) would be 18″-36″ tall, while a tree with a 1″ trunk would be no more than 6″-12″ tall. These rough proportional guidelines give a starting point when looking at stock to determine how much can be used, particularly for the beginner. As we learn more we begin to understand the exceptions in both directions to this rule – a shohin tree with a 4″ trunk that tapers to a perfect canopy in less than 8″ gives us a girth:height ratio of 1:2. Another exception – a bunjin tree with a 1″ trunk that is 36″ tall with elegantly spaced branches gives us a ratio of 1:36. Trunk size alone cannot tell us everything about the proper proportions for our bonsai, we still need to take into account a few other things.

Fig 1. Comparison of a typical Japanese maple from nursery stock and a bonsai Japanese maple. The nursery stock (left) has long branching without taper. The usable portion is normally the lowest portion of the trunk (middle). After a few years of branch development the tree can be a good bonsai (right) with proper taper and proportion between the trunk and branching.

Trunk taper 

Taper is perhaps the most important determining factor of height and overall size in bonsai. The trunk that starts at 6″ diameter and tapers rapidly and evenly to 1″ diameter in 12″ of vertical space cannot be extended to a 18″ tall tree while keeping good proportions. The tree needs to be short and fat because the trunk is short and fat; adding a skinny section of vertical trunk above the rapidly tapering section will only make the tree look awkward (see figure 3B). Conversely, a 6″ trunk that tapers to only 5″ in the first 18″ will likely look better as a taller tree – one in the 24″-30″ range (figure 2B).

Fig 2. Trunk taper is one of the keys to a good bonsai trunk. Trunk A is not suitable for a bonsai – with proportions similar to a telephone pole it is very difficult to use this material for a bonsai. The only recourse is to cut it at a height about 1.5x the diameter and hope for buds. Tree B is typical of many collected trees – the trunk has a slight taper leading to a large chop. This material is usable but needs a lot of time to develop into a good bonsai. Trunk C has excellent taper and is a well-suited to bonsai; this type of trunk is normally only found in high-quality nursery-grown stock that is specifically for bonsai.

Trunk angle 

The angle that the trunk makes with the ground helps determine the proportion and also helps indicates the style in the composition. A tree that exits the soil vertically can typically only be a formal upright tree. A tree that makes a steep but noticeable angle to the ground is usually an informal upright. Semi-cascade and cascade style trees typically exit the soil at a 45 degree angle or even lower. The angle of the trunk also interplays with how much movement should be in the trunk of the tree. An informal upright that exits the soil at an 85 degree angle should have only subtle movement while an informal upright that exits the ground at a 60 degree angle should have much more exaggerated movement through the rest of the trunk. If the trunk exits the ground at a 60 degree angle but has only subtle movement then it is more well-suited to a slant-style tree.

Branch and apex details 

The proportion and placement of the branches and apex will form the basis for the eventual silhouette of the tree. The primary branches should always be significantly smaller than the trunk, a problem that is harder to avoid on trees with small trunks. When branches approach about 2/3 the size of the trunk our eye begins to confuse the branch with the trunk line. The taper of the branching should match the taper of the trunk – a short well-tapered tree should have larger branches than a tree that has a tall and skinny trunk.

Length in the branching is somewhat more important than taper – while taper can be overlooked as a minor flaw the length of the branches will determine the silhouette of the tree and thus the overall visual mass in the composition. Consider the visual mass of the entire composition against the visual mass of the trunk. A tree with a thin trunk and a large volume of branches may work for some species like maples while not as well for others like pines and junipers.

The secondary branches should be significantly smaller in most compositions than the primary branches. The branches will look more mature the more divisions you see between the where the primary starts and the tips. In a good bonsai there will be many branch divisions in a short space. Typically this happens over a few to many years by repeatedly removing longer growth in favor of growth with shorter nodes and finer branching. When growing out material with no branches allow the branching to lengthen, then wire the branches and allow them to continue growing. After the branch reaches a good size cut back to start building secondary branching; depending on the species this process may take place over 1-5 years. The process of cutting back will increase the taper in the branching while also stimulating the secondary branches to grow enough to be wired to harmonize with the primary branch.

Fig 3. Good branch placement and proportion can make all the difference in a composition. Tree A has poor taper in the branching and the branches are too long and not matching in angle. The apex is also too tall. Tree B is a poor use of good trunk material; the trunk and branching/apex are dis-associated from each other. The taper is poor because there is good taper in the main trunk section and no taper in the upper trunk section. Tree C has good branch placement and apex formation – they are all in good proportion to the trunk.

While it may make sense as we read these rules to mentally apply them, it is sometimes a bit harder in the process of looking an actual tree to make a decision about how to make it more proportionally appropriate. Starting with the trunk, and even in established material when appropriate, consider removing any sections that have little taper and movement in the upper half. This may mean losing the established crown of the tree! But the trade-off is a tree that will be much more compact with a properly developed crown.

In the branching, particularly on deciduous material, consider starting completely from scratch if the branching is poor; this may only require the fortitude to cut all the existing branches off. Many trees that have branching like figure 3A can become Figure 3C with a few years worth of diligent effort. For conifers the process can be more complicated. Consider grafting on new branching to re-position the crown or to make the tree more compact. While back-budding can be useful on some species of conifers, on others it may be more expedient to simply graft new branches. Heavy bending can also sometimes correct proportional problems. If a coniferous tree has good taper in the lower trunk but poor taper in the upper trunk consider bending the trunk to move the foliage closer to the lower trunk.

Fig. 4 (A) – as a conifer this tree is far out of proportion; the branching is too extensive to allow an appreciation of the trunk line. As a deciduous tree it may be acceptable but in both cases it could be improved. As a deciduous tree such as an elm, remove all the long branching (B) and wait for shoots (C) then wire the shoots and train the branches until a tighter silhouette is achieved (D). As a conifer cutback would need to be in stages, or grafting would be followed by cutback.

The proportions of a tree can go almost as far to the short extreme as you can push them. Extreme trunk taper and small branching are generally considered desirable characteristics. On the other hand, lack of taper leads to overly long branching, uninteresting trunk sections, and apexes that are visually divorced from the most interesting parts of a tree. Taking the time and making the effort to understand how proportion affects the composition will improve your bonsai trees significantly.

(originally published on the Bonsai Society of San Francisco website, written by Eric Schrader)

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