Developing Deciduous Bonsai Branch Structures

Part One: Building a Branch Structure: Page 2 of 2

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This series of four articles first appeared as part of Chapter 12 of my first book Bonsai Inspirations 1 and this excerpt contains what I believe to be essential information on how to design, build and improve the branches and branch structure of a deciduous or broadleaf bonsai.

Note that extensive information of how to build the branch structures of coniferous bonsai, such as Juniper and Pine, are contained within Bonsai Inspirations 2

Part Two>> Autumn/Winter or Structural Pruning and Wiring

Part Three>> Shaping Deciduous Tree Branches

Part Four>> The Importance of Branch Taper in Bonsai


Page 2 of 2:

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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).

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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.

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Elm stump in June 2006.

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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.

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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.

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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.

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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.