Developing Deciduous Bonsai Branch Structures: Part 1



Developing Deciduous Bonsai Branch Structures: Part 1

The main principles to understand when developing new trunklines (new ‘leaders’) or branches on bonsai are as follows:

The shoots (be they potential branches or leaders) with the most growth will thicken the fastest.

The shoots with the least growth will thicken slowest.

To encourage growth in a shoot, do not prune that shoot.

To encourage maximum growth in a shoot, prune all other shoots on the tree.

To stop a shoot growing, pinch back that shoot.

To minimise growth, do not let the new growth extend (by pinching the new growth as it opens)

Using these 6 basic principles, the bonsai enthusiast can control which parts of a tree grow and eventually become thicker and which parts remain as they are.

Developing a branch structure and new leader on a bonsai using these principles can sometimes be something of a chinese puzzle. However, if one is focussed on which areas of the tree (the leader or the branches or a particular branch) require the most growth and which areas of the tree require the least, it is a solvable puzzle!

Using the Elm airlayer featured in Chapter 12 of Bonsai Inspirations 1, I will now illustrate how these 6 principles are applied to a tree stump in order that it can be turned into a bonsai.

This process, or parts of this process, can be applied to all deciduous trees whether they be completely raw material, a fully formed trunk that requires a new branch structure or even a fully developed bonsai.

bonsai branches

At the beginning of the first year of developing the stump, (assuming it is healthy and vigorous) it will produce new buds all over the trunk. These buds will then begin to open into new shoots as temperatures warm in the Spring.

A bare trunk stripped of all shoots and branches in the Autumn will produce considerably more buds from the trunk during the following Spring. Any existing branches that are left after Autumn pruning will reduce the number of buds that appear on the trunk itself.

bonsai branches

The first step for the enthusiast to take, is to decide which new shoots to keep for development into new branches and trunk leaders, and which to remove. The sooner that unwanted shoots or preferably buds, are removed, the more ‘energy’ the stump is able to divert into growth and development of the shoots that are wanted.

The exact shoots or buds to keep will depend on the future design you have for the tree and if you are not 100% certain whether a particular branch will be required in the future, keep it for the time being. In the future it will always considerably easier to remove a bud or shoot you are undecided upon, than it to regrow it again.

bonsai branches

At this point it is important to understand or remind yourself about apical dominance. Every tree species will have a natural growth habit that will produce different rates of growth in shoots depending on their position on the trunk. At the uppermost part (a) of the tree (be it the top of the trunk and branches at the very top of the tree), growth will be strongest. This means that there will be more buds appearing in this area, the shoots that they produce will be more vigorous and will have a greater growth rate. Conversely, in the lowest areas of the trunk (c), bud production and shoot growth will be weakest. The areas inbetween (area b) will tend to have bud production and shoot growth rates inbetween areas (a) and (c).

This principle is pretty straightforward. However, it should be noted that different tree species naturally have different degrees of apical dominance. For our purposes as bonsai enthusiasts, there is no exact science in explaining these differences. Various tree species are just variously described as being ‘ a little apically dominant’ or ‘very apically dominant’. It is only with experience that one can establish what these descriptions actually mean in practice! There are also a much smaller number of tree species that can be described as being ‘basally dominant’. In these cases it simply means that the base of the tree is the most dominant part of the tree and the top of the tree is the weakest and the strengths and weaknesses of areas (a) to (c), are reversed. So, bearing in mind the growth tendency of the majority of deciduous trees, if the tree stump in this example were to be allowed to grow freely without our intervention, the leader at the top of the trunk would grow the most and thicken the most.

bonsai branches

In this case that is what we hope to achieve, maximum growth in the new trunkleader so that it will thicken as rapidly as possible, creating better taper to the top of the stump. However, without any pruning, the new shoots in the middle part of the tree (area b) would grow faster than those shoots in the lowest areas of the trunk (c). This would produce branches in area b that were thicker than the branches in area c. This is the opposite of the desired effect in bonsai where the lowest branches are also the thickest.

A second important effect of leaving the remaining shoots unpruned is that some of the tree’s resources or energy would be wasted growing these middle branches. Pruning the growth of the middle branches will divert the tree’s resources to the trunk leader to ensure maximum growth.

And so, the correct way to deal with this example tree is allow the new leader to grow freely. To allow each of the middle branches to extend and open 3 or 4 leaves and then pinch out the rest of the new shoot so it will not extend any further leaving the tree’s resources to be diverted elsewhere. The shoots in the lowest parts of the tree need to be thicker than the shoots in area (b) and should therefore be allowed to extend further than the shoots in area (b), and are left to grow until around 8 or 9 leaves before being pinched out.

The result of this pruning or pinching out will be something akin to the diagram on previous page.

bonsai branches

When the new leader has begun to grow strongly it is time to consider carving the top of the trunk to create better taper to the trunk.

The preferred time to do this on deciduous trees is during the growing season, preferably after the first flush of growth has hardened off.

At this time of year the wound resulting from chopping the trunk heals relatively quickly and callus formation (to cover the exposed cambium and to begin the years-long process of covering the large wound) is at it’s most rapid.

Carrying out this work during the dormant season or during early Spring is unlikely to harm the tree itself but healing of the resulting wound will be slow or non-existant if carried out in the Winter.

An imaginary line can be made from the base of the new trunkleader sloping either sideways or backwards (so that the resulting wound is not visible from the front of the tree) using a sharp knife and the excess bark and wood can be removed.

bonsai branches

Actual physical removal of the excess wood can be difficult on thick trunks and requires the use of power tools as well as saws. However, where the top of the trunk has a smaller diameter, knob cutters are often sufficient and the excess wood can be removed bit by bit.

bonsai branches

Actual physical removal of the excess wood can be difficult on thick trunks and requires the use of power tools as well as saws. However, where the top of the trunk has a smaller diameter, knob cutters are often sufficient and the excess wood can be removed bit by bit.

bonsai branches

Note that the more of a downward slope you create when cutting the trunk back, the better the taper you create in the trunk. However… the more taper you create, the larger the wound and the longer it will be before it heals over (if it heals over completely at all).

With some species such as Elm there is a good possibility of new buds and shoots appearing along the line of the wound. However, on species that will not do this, the lack of new buds and shoots in this area can leave a large empty gap in the branch structure.

bonsai branches

September 2005: just a year later and the Elm has grown well.

This Elm stump (pictured above) has been tapered just a week ago and has begun to heal over already. As you can see I have taken the taper from behind the top of the trunk section down to a new shoot; the presence of a shoot at the edge of a large wound will always speed up healing.

Notice that I have used a wound sealant on the edge of the wound to seal the newly cut cambium layer itself but a layer of petroleum jelly is sufficient for this job and is considerably more preferable on trees with resinuous sap such as Pines, Larch and Spruce.

bonsai branches

By the end of the first year of development, (depending on your feeding regime, the vigour of the tree and the species used), the stump will look similar to that shown above.

Due to the pinching out and pruning of the shoots according to their position on the tree, the new trunk leader is the thickest shoot, followed by the lowest branches, with the branches in the middle of the tree being the thinnest.

Note that after pinching out the new shoots in the Spring, each will have been very likely to produce at least two new smaller shoots at the pinching point. If and whenever this occurs during the growing season, the same process of pinching out should be carried out on the newest shoots.

bonsai branches

At the end of the growing season (or in certain climates at the very beginning of the next growing season) the stump’s growth must be pruned back.

Here in the UK, Winter temperatures rarely fall below -7º and never below -10ºC. This allows enthusiasts to prune and wire their fully-hardy bonsai during the late Autumn immediately after leaf-fall. In areas where Winter temperatures drop below -10ºC and bonsai can’t be protected against this degree of cold, it is recommended that pruning and wiring is not carried out until the Spring when temperatures begin to rise.

Cutting back the current year’s growth creates better branch taper in the future; the new shoots that will appear on the branches in the following year will always be distinctly thinner.

New shoots grown in the same growing season as each other will always end up being the same diameter, even when comparing shoots that grew in the Spring and late Summer as each other (as I found out after trying to build branch taper on a small bonsai over the course of one growing season!).

Therefore, if the pruning back of the branches (when developing the branch structure) is not carried out inbetween growing seasons , the lack of taper will be obvious in the future.

More discussion on the principles and technique of branch development and ‘Winter’ pruning is continued later in this Article Series.

The basic principle of pruning this Elm airlayer at the end of the first season of development is to prune according to the apical dominance and the individual development of this tree.

That is, the new trunkleader is not pruned at all as the process of thickening the upper trunk has yet to be finished.

The new branches are pruned according to their position on the trunk; the lowest branches in area (c) are pruned back hard to just 3 or 4 leaf-joints and the middle branches in area (b) are pruned back even harder, to just 1 or 2 leaf-joints.

One important consequence of pruning back this hard is that it will encourage further production of new buds from the trunk and is an opportunity to fill out any empty spaces in the trunk with new branches. Indeed, this maybe the last opportunity for this event to occur without having to remove all of the branches again in the future.

Those that are not required for the future design are removed to divert the tree’s resources into development of those that are.

bonsai branches

New shoots are then pinched out as they extend with no interruption in the growth of the trunkleader, pinching out of the lowest and middle shoots according to their position on the tree.

By this stage in development, it may become noticeable that there will also be shoots with atypical growth rates. It is not unusual to have a very weak shoot in the middle area (b) of the trunk that should not be pinched out as early as the other shoots in area (b) so that it can thicken a little more.

Conversely there maybe a shoot in the lower part of the trunk that is considerably stronger than would be expected considering its position. Such a shoot can be safely pinched out earlier than would be normal.

Notice that I have made no mention of repotting at the beginning of the second year; unless there is a strong reason for repotting and/or root pruning the tree (issues with poor soil, an urgent need to shape the nebari etc), allow the roots free growth to encourage the fastest possible development of the trunkleader.

bonsai branches

By midsummer of the second year an Elm will have had the appearance of the new Spring shoots that have then been pinched out; resulting in a second flush of shoots that should also be pinched out. This process of allowing varying degrees of growth that is then pinched out (and pruned back if necessary) carries on throughout the growing season.

For some vigorous tree species this process can need to be repeated 4 or 5 times between Spring and Autumn, with other species or with weaker trees, there maybe only 2 or 3 new fl ushes of growth in a growing season.

bonsai branches

By the end of year two, the Elm can easily be as well developed as the illustration above. The branch diameters are in accordance to their position on the trunk and the trunkleader is now thick enough to make a convincing trunkline.

bonsai branches

Winter pruning Year Two. The branches are all pruned back hard in accordance to their position on the trunk and their vigour in the same way as they were at the end of Year One. With the Elm airlayer’s trunk leader having reached the desired thickness, all of the top growth is chopped back to a thinner side shoot. By comparing the two images above it is possible to see that by chopping back in the way that I have done, the trunk now has a smooth tapering trunk with good movement.

One mistake that I often see by beginner enthusiasts is to not be brutal enough when they chop back resulting in the top of the trunkline looking too long and taperless itself, while the unnecessary additional height reduces the power and strength of the tree itself.

However difficult it maybe to reduce 2-3 years worth of growth and a metre or two of live wood to just a few centimetres, it is an essential apect of trunk-building to then be able to reduce the growth back properly.

It is important to understand that once the trunkleader has been chopped back and the top sacrificial growth removed, in the future it will not noticeably increase in diameter as growth from the top area (a) will always been tightly controlled to ensure that the uppermost branches of the bonsai remain thinner than those in the middle and lower areas of the bonsai.

If the trunkleader is not thick enough to make a smooth transition up the trunk from the original stump, it should be allowed to continue to thicken. (Note that the process of chopping back the trunkleader can also be made during the growing season, this part of the technique is not limited to the dormant season).

bonsai branches

Year Three: In the Spring, with the trunkleader having been pruned back so hard, a large number of very vigorous buds will appear at the top of the trunk. It is important at this time to be very diligent about removing un-needed buds and pinching out the new shoots.

Now that the trunk and trunkline has been fully developed, the balancing of vigour throughout the tree will change. Development of the uppermost branches (the apex or crown) begins and the shoots that grow here must be thinner and weaker than those in the middle and lower areas of the tree.

This requires that any new shoots in this uppermost area are only allowed to extend and open 1 or 2 new leaves before being pinched out while shoots in the middle area are allowed to extend by 3 or 4 new leaves and the lowest and naturally weakest shoots should be allowed to extend to 5 or 6 new leaves.

This process of redressing the energy and vigour of the tree continues throughout its life and the basic principles concerning growth and thickening of the branches can continue to be applied wherever necessary. Branches that are too thin for their position on the trunk (in particular lower branches) can be allowed to extend (grow) longer in order to thicken them faster than the other branches.

It can also be ensured that branches in the uppermost areas of the trunk do not become too thick by pinching them out.

bonsai branches

Elm stump in June 2006.

bonsai branches

The Elm stump in December 2006 having concentrated growth into the new trunkleader.

From June 2005 through until the Winter of 2007-2008 I continued to develop the Elm as described in this article.

bonsai branches

January 2007.

The new leader was allowed to grow freely for 2½ years until it was thick enough to create convincing taper into the stump and then in early Spring 2008 it was chopped back hard to a thinner shoot low down on the new trunk.

bonsai branches

After chopping the trunkleader in early Spring 2008.

After chopping the new trunk leader in early Spring 2008. note that the very top shoot was being used to graft a new branch into place near the large wound on top of the stump, hence the strange angle of growth!

As can be seen in the image above, I have wired the developing branches into shape and have left some of them unpruned so that they will increase in diameter more quickly next year.

bonsai branches

Autumn 2009.

Autumn 2009 and the tree has continued to develop well during the previous 18 months. As is typical of all apically dominant trees, the branches in the upper part of the branch structure have been very quick to grow and develop.


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November 16, 2022


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