Leaves: Part 2 – Reducing the leaf size in bonsai

By September 23, 2017 No Comments


The size of leaves in nature plays an important role, since they works like a solar panel, the bigger they are, the more light they absorb.  This absorbtion of light along side other factors briefly discussed in the previous blog encourage photo synthesis.  Nature balances itself, and this balance is every where.  A plant or tree balances itself by balancing the foliage with the root system.  A tree with large leaves is also balanced with another tree with smaller leaves, so while the first one has less leaves, the second tree has more smaller leaves, (refering to healthy trees).

Trees grow upwards

Each tree will do it’s utmost to maintain herself healthy, growing upwards searching for more light, mostly if that particular tree is surrounded by other species.  The location plays an important role in the growth of the tree.

  1. A tree growing in a flat area with no competing trees captures light from all over, so it has an equal growth around the tree.
  2. Trees that forms part of a forest has limited light, and this limitation will force the tree to grow longer in search of more light.  This is the reason why trees at the core of a forest are longer than trees at the edge of the forest.
  3. Apart from light in the trees location there are other factors such as wind and snow that shapes the tree’s growth.  Although such trees might be surrounded with light, but strong winds and snow will challenge how the tree grow, bending and twisting it to grow in an irregular and unnatural way.


The meristems helps the tree to grow.  In a tree or plant, there are three different meristems:

  1. The ‘Apical Meristem’:
    1. Are found at the apex of the tree or plant, and are responsible to growth in height.
    2. The meristem at the tips of the roots are also called apical meristem.  The are responsible for the growing of the roots length wise or as also known as the primary growth.
  2. The ‘Axillary Meristem’:
    1. The axillary meristem are responsible for the lateral growth of the tree, and these meristems grows from between the stem and the leaves, resulting in branches.

The three different meristems

The meristems can grow to a new bud that helps the tree or plant to grow longer or wider.  They are also responsible for the new growth of flowers and leaves.

The Tree Calendar

Trees will encourage new growth in spring and will let fall leaves during the dormant season.  What makes this phenomenon?

The light of day gets shorter as soon as autumn will approach and the temperature will decline.  These are the signs that makes trees to go dormant.  On the other hand, the longer the day of light and the rise in temperature will encourage the tree to start producing new buds in the spring time.  The most important is the shorter day time and equally important is a longer night time.  In such situations, trees starts to shut down to dormancy.

Protecting the buds from the harsh weather in winter time by hardening the buds is part of the dormancy process.  These buds will start to grow again in spring.  There might happen that hot sunny days might occur in later autumn and some of the buds will emerge out of season.  Since they grew out at the wrong time, and the hot days are short, they will die back.

Seasonal changes on deciduous trees

Smaller leaves and shorter internodes

The tree is in constant motion to maintain the balance between the foliage and the root system.  The balance happens in spring when the tree pumps the stored energy in the root system to produce new buds and flowers.  In summer, this processed is reversed, when leaves will supply the root system with sugar.  These two systems together encourage top and lateral growth.  During winter time, the leaves will stop producing the necessary sugar, but food previously produced will continue to move towards the stem.  This will help the roots to grow and increase their size, as a reserve, to restart the process again the next spring.  The roots will stop growing when the soil temperature will go below 60 degrees.

Let’s translate this process to a bonsai language.  Removing essential buds during the dormancy period, will unbalance the system, and when new buds emerge in spring, the over stimulation of food stored in the roots will encourage longer internodes and large leaves from the lesser number of buds available.

Shorter internodes creates a better looking bonsai

On the other hand, if you trim off the root system, that is the food supply, during the dormant season, the result is that the tree will encourage shorter internodes and smaller leaves.  The tree will balance itself between the root system and the foliage.

The partial removing of the root system should not be very aggressive.  Tress store energy in their root system, so by removing a large amount of roots, the necessary energy the tree needs to continue it’s cycle will be thrown away and eventually dies.   It is recommended that less than 20% of the whole rooting system will be removed in one go, and that means while repotting: which is carried out every three to five years.

Even the removal of the 20% of the root system is not a fixed number.  One should consider the age and density of the root ball of each tree.

Fertility level

Those who have olive trees as part of their bonsai collection, might have noticed that every year, these trees does not grow all together and they will vary their growth differently every year.  The reason for this is that each tree has its own fertility level, and this varies according to many factors.  One factor we will mention is that after a repotting, the fertility level of an olive tree lowers down, since it needs to gather necessary energy lost during pruning or the branches and roots.

Fertiliser and leaves sizes

Constant feeding will result in normal sizes leaves and internodes, so although not really recommended, less fertiliser will help in the reduction of the leaf size and internodes.  This should be carried on young trees to produce close internodes in the lower part of the trunk.  When feeding, nitrogen is the nutrient responsible for leaf and internodes growth, so when we said less fertiliser, it means less nitrogen to the tree.  This can be carried out in two ways:

  1. Add less percentage than recommended on the packaging
  2. Extend the date between fertilising

Fertiliser is divided into three main parts: N – P – K

Pruning as a way to decrease leaves and internodes size

On pruning, the tree will be losing the food factory (photosynthesis), so the stored energy in the root system will have to produce a set of new leaves all at one go.  So energy has to be divided into all the new buds,  producing smaller leaves and shorter internodes.  This is only carried out on deciduous trees such as olivaster, ficus etc.

Defoliation helps to reduce the leaf size

On juvenile trees, this process needs to be carried out twice a year:

  1. Mid to late April: after the first buds have settled
  2. Early to mid September: when it is still time for the tree to make a set of new buds

On matured trees, this process should be carried once a year:

  1. Mid to late April: after the first buds have settled


Make sure that defoliation is carried out ONLY  on healthy trees.  The best way to defoliate a tree is by using a sharp sterilised shear to cut away the leaf from the base, leaving the stem attached to the branch.  The stem will fall naturally once it dries out.

A set of new leaves will sprout all at once and just after few days, 7-10 day.  After a month you will notice that the leaves are smaller in size and the internodes are shorter.

It is important to keep the tree in bright sunlight.  If kept in the shade, the tree tends to search for more light, so the internodes will become very long than normal.

Defoliation is carried out on healthy trees

Other benefits

There are other benefits that defoliation offers to a tree.

  1. The defoliation stress of is spread out for months
  2. Ensures excellent condition of foliage at the lower zone of the tree
  3. By removing the large leaves normally found at the end of the branch, light is permitted to pass more freely to the lower zone and inside the tree, encouraging vigour to unhealthy branches in those areas
  4. Defoliating the apical zone will help to reinvigorate the lower zone of the tree

Olive tree after defoliation

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Martin Abela

Author Martin Abela

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