by Colin Lewis

This article appears on the author’s web site and is reprinted with permission of the author - ED

One of the initial fascinations with bonsai is that of their age. But just how important is the true age of a bonsai, and can true age be simulated?

Natural aging of trees

Trees don’t age in the same “linear” way as animals. Animals transmute from infancy to senility in a strict chronological progression. Their physiological age - as marked by factors such as body shape, skin texture, hair color etc. - and their “reproductive” age are precisely controlled by their chronological age. Animals have, in a sense, only one growth phase - from birth to natural death.

Trees, on the other hand, have separate chronological, physiological and what Dr Peter Tredici of Harvard University’s Arnold Arboretum refers to as “ontogenetic” aging processes. The three phases of maturity develop independently, and at different rates in each individual tree, and even at different rates on different parts of the same tree.

For example, the chronologically oldest part of any plant is the cotyledal node, the section below where the first two “seed leaves” were borne. Ironically, this is also always and permanently the most juvenile part.

Conversely, if we take as an example a hawthorn which flowers regularly, the flowering spurs are the newest (chronologically youngest) parts of the tree, but they are ontogenetically the oldest or most mature. As an array of twigs begins to flower, they transmute from ontogenetic juvenility to ontogenetic maturity. There will no longer be the annual flush of extension growth unless the mature sections are cut back to the juvenile buds at the base of the twigs. At the top of the same tree, however, there may well be areas where annual extension still occurs. In these juvenile areas there will be no flowers.

With some species the growth pattern is an indication of maturity - but not necessarily of age. Larch, cedar and ginkgo all have two types of shoot growth: vigorous extension shoots and short “rosettes” of foliage borne on spurs, which only extend by a millimeter or less each year. Young seedlings have almost all extension growth; a sapling will have many rosettes but still produces vigorous annual extensions. An old tree will bear almost entirely spur growth.

Simulation of age in bonsai

Some of the most common questions asked by the public at any bonsai exhibition or nursery are, “How old is that tree?” or, worse still “How old are some of these trees?” After the umpteenth time, it’s difficult not to become a little irritated. John Yoshio Naka once came out with the perfect reply: “But sir, you never ask a beautiful woman her age....”

This encapsulates the significance of age in bonsai - at least as far as aesthetics are concerned. It is how old a bonsai looks that is more important than old it actually is. If the design is intended to represent a 500 year-old pine, then the bonsai should have all the characteristics of a 500 year-old pine: fractured bark; fine, tight foliage; open branches with angular bends; and, of course, a domed (rather than pointed) crown.

Of course it helps a great deal if you can start with a plant that already has some or all of these characteristics. Old yamadori provide the quickest route, but they can have their drawbacks. As often as not, it is necessary to do heavy cutting and carving to reduce the size and to disguise the removal of heavy branches. This is extremely difficult to do convincingly, and once done badly, can never be rectified. Additionally, the new branches that are grown and trained by the artist are inevitably more juvenile in character, so the problem is still not entirely solved.

There are some techniques which can be used to increase the apparent age of a bonsai - some taking more time than others to have an effect. None of them are quick-fire solutions.

However, when we talk of the appearance of age in bonsai terms, we are generally referring the apparent evidence of physiological aging. These can be distilled to five characteristics:

1. A domed crown
2. The poise of the branches
3. Angular branch ramification
4. Distinct, separated foliage ‘clouds’
5. Mature bark texture how bark is formed adding character to bark

The first four are relatively easy to impose with wiring and pruning, so they don’t need to be discussed in great depth here, but a few words may prove useful. Then I will deal with bark texture in greater depth.

The Crown

To create a domed crown, it’s necessary to forget the concept of “wiring in a new leader”. This is only done while the trunk is being developed. Once that is finished all thoughts of a leader are abandoned. The apex should then be thought of as a central, apical branch. It should be constructed in precisely the same way as any other branch, with one difference - the limb that supports the apical branch structure approaches from below rather than from one side.

Branch Poise

Although the principles of branch positioning are straight forward, it is something that is often compromised during the initial design stages in the rush for a finished image. Old conifer branches sweep downward and old broadleaved branches are more or less horizontal - at least in the simplified world of bonsai. In neither case will arching branches convey the impression of age. All too often this realization comes years after the branches have set and have become too thick to change. The best advice is to get the branches right at the outset.

Ramification

There’s fine ramification and there’s fine ramification. A broom style bonsai may have millions of tightly packed minute shoots. It will look well developed, mature, but never ancient. It simply isn’t that kind of image. So ramification alone doesn’t achieve the appearance of age, but HOW the branches ramify does. Sharp angles, switchbacks, dramatic taper, are all indications of age. The absence of thin laterals growing from the inner portion of the main limbs, short distances between bends and forks, and restricting short foliage-bearing shoots to the peripheral areas also contribute. Old trees do not have long central branches with alternate laterals forming a triangular framework, any more than they have pointed apices. Such branches are fine for the initial stages of building a bonsai but they should be cut back at the earliest opportunity. These are all points to consider, not just during the initial shaping, but every time you prune or wire. Regardless of the age or developmental stage of the tree, there will always be opportunities for improvement.

Foliage Clouds

As time passes and ramification increases, the foliage on a mature bonsai can become one solid mass if not properly attended to. A solid green “blob” typifies a shrub or, at best, a young tree - no matter how the trunk and branches are formed. In general, as a tree reaches old age, the foliage masses become sparser and more isolated from each other. Each individual “cloud” also becomes more fragmented, appearing to consist of many smaller clouds. Spend some time studying some of your more established and well-developed bonsai, and consider whether removing one or two branches, or thinning out the clouds to fragment them a little might not improve the image and add apparent age. You’ll be surprised at what you discover.

Bark texture

Mature textured bark is arguably the most precious feature of almost any bonsai. With immature bark, few bonsai can appear mature. The exceptions are species such as many acers. taxus, fagus etc., where the bark remains smooth throughout the tree’s life. But most species produce a characteristic mature bark as they mature, usually adopting a fissured or plated texture. Others, such as pseudocydonia and platanus have bark which flakes in patches to reveal many subtle shades of pink, green and buff. Betula and many prunus species allow their bark to peel in colorful layers.

How bark is formed

New layers of bark are formed annually in much the same way as the annual rings are formed beneath them. The singlecell thick cambium layer produces new wood on the inside (the xylem) to conduct water and nutrients to the leaves, and new tissue on the outside (the phloem) to conduct sugars from the leaves to the rest of the tree. As each new layer of phloem is formed, the outermost dies and becomes bark.

The reason why mature bark differs between species is complex, and not yet fully understood. But in bonsai terms, we’re more concerned with discovering how to accelerate its development.

Speed of growth is not the controlling factor. If a tree grows very rapidly, it can reach a considerable size and age but not display mature bark. The dying phloem remains elastic, and the ‘stretching’ process associated with rapid trunk expansion retards the development of bark texture. There are two main influences on early bark maturation, one internal and one external.

Internally, it is the amount of phloem laid down annually in comparison with the trunk expansion that determines how quickly the bark will mature. A slowly expanding trunk, but with a heavy annual deposit of phloem, will produce more bark. The bark becomes thick because it is not being stretched. The amount of phloem produced is governed by the amount of foliage, so a tree whose growth is retarded by external forces, but which bears copious amounts of foliage will produce mature bark rapidly.

We can use this knowledge when we grow material in open ground. Allowing unfettered extension to thicken the trunk is only half the story. Once the trunk has more or less reached the desired thickness, let it stay in the ground a few more years. Build up as much weight of foliage as possible without allowing long, vigorous leaders to grow. When you finally pot up, you’ll have material that has mature bark character that would take decades to develop in a pot.

Adding character to bark

Externally, the immediate environment around a trunk seems to have an effect on the bark. With the exception of Betula, which are colonizers of open ground and develop silver bark when grown with their trunks exposed to full sun, most trees develop mature bark quicker when their trunks are surrounded by vegetation. The constantly moist ambient, where the bark is protected from the scarifying effects of the elements, can dramatically accelerate the process - and more so when trunk expansion is slow, as it is likely to be when the tree is competing with the surrounding vegetation for nutrients.

We can simulate these conditions on a bonsai of any age or size to improve the bark texture by following the three steps of the “Sphagnum Wrap” technique:

ONE: With a piece of coarse abrasive paper, very gently stroke the trunk in a vertical direction once or twice to penetrate the outermost “skin”. Don’t go as deep as the cambium, and remember that you’re not trying to remove the skin, just to score it in a few places. Go as high on the trunk as you can and, if possible, include any heavy lower branches.

TWO: Take some moist sphagnum moss (or any other dead, water retaining vegetable matter) and pack 20mm layer LOOSELY around the scored area. Hold the moss in place with twine, wire or open mesh of some sort, making sure it’s not compacted at all.

THREE: Keep the moss wet at all times, even if this means placing the tree in the shade and heaping extra moss around the trunk in dry weather. Inspect the trunk every month or so to make sure you’re not inadvertently layering the trunk! If you see roots forming, break them off and remove the moss for a couple of days, replacing it as soon as the bark appears dry.

This procedure prevents the normal drying and erosion of the outer “onion-skin” layers and allows moisture to soak into and expand the still porous spent phloem. The time required for fissures to appear will depend on the thickness of the existing bark itself and the amount of new phloem produced during the process, but be prepared to keep the “sphagnumwrap” in place for up to two years, possibly longer. Allow the tree to bear as much foliage as possible to maximize the phloem production. Balancing this need with the need to maintain shape can be tricky, but even if you have to spend a year or two re-refining the branches, the improvement that mature bark will bring to your tree will be well worth the wait.