Introduction – The pruning of a bonsai tree is probably the most important single factor in the forming of its shape, perhaps more so with deciduous than with conifers due to their rather intensive growth. Pruning as such can be divided into four main headings, Root, Heavy branch, General and Leaf. When pruning roots and foliage it is often stipulated that what percentage removed from the roots should be reflected in the foliage and visa versa, because this reduces stress maintaining a balance between the tree’s two sections.
Nonetheless, there are those who disagree they contend that some deciduous species can have their foliage completely removed in the growing season to encourage new growth. This Ginkgo biloba spends the colder months (October to May) inside under LED grow lights with a constant temperature of 24 degrees C. Complete leaf drop occurs when it goes from inside to outside (late May) but, within 4-5 weeks it is back in leaf. This situation repeats itself when it is returned indoors, (mid September) thus the tree loses its foliage twice in a relatively short space of time; an 8 to 10 week period of no foliage, which does not effect the tree’s health. The reason why leaf drop occurs twice is due to environmental change – not the plant entering dormancy.
To further this discussion a Himalayan juniper Juniperus squamata was obtained in early spring 2021, according to the fact sheet this plant should be located where it receives full sun; a minimum of 5 to 6 hours per day. We decided to experiment by adopting a different approach, a round Japanese bonsai pot was selected, but as the tree had a large root ball, 60% of it was cut away in order for it to fit the pot – none of the foliage was pruned resulting in an imbalance between root and foliage. The plant was then placed in a location that has full shade and as the image shows, the plant is thriving with no ill effects; this juniper will be left for a few years before styling begins.
The argument of maintaining an equal balance between root and foliage has theoretical logic and in many cases may prove to be correct with certain species of plant but, as we have demonstrated here there are instances where such logic does not apply nevertheless, debates on this subject will no doubt continue.
Root pruning – is carried out periodically because bonsai grow in small containers. Such confinement forces the root system to encircle the entire pot area saturating it in a dense mass, the result is the plant becomes ‘pot bound’. In this situation it begins to suffer because the much needed nutrients have been exhausted, circulation of air in the root mass is restricted and watering retention is increased. Deciduous species can be rigorous in their growth, hence it is prudent every 2 to 3 years to lift the plant out of the pot to check the roots ball’s condition whereas, coniferous species can be checked every 5 to 6 years, but much depends on the species and variety.
Foliage pruning – In 2017 we acquired a common juniper Juniperus communis which was trained as a cascade, (Kengai) it was left to grow and conform to its new design until July 2021 when pruning was much needed as the cascade appearance was masked by excessive growth. Branches had intertwined and were invisible, foliage was dense creating a hiding place for unwanted minibeasts moreover, it restricted air flow. Below are two images of this plant – before and after.
As one can note there is a marked difference in this tree’s appearance and arguably there is improvement, but there is a lot more work to be done pruning wise. In addition, those with a keen eye will notice that this tree lacks a ‘top knot’ or crown, the original 3 branches at the top succumbed to the 2017 winter period and were later given a Jin or shari look. However, there is a small shoot protruding out from underneath the upper most bend that hopefully will replace those that were lost.
The next plant to be given hard pruning is this Sea Buckthorn Hippophae rhamnoides being trained in a Literati or Bunjin style. In the left image the foliage is masking the branches of which there are 3 as shown in the right image with the top one the main branch. This branch when dormancy arrives will be wired into shape and allowed to extend further down towards the container, the other two branches will probably be reduced and wired into new positions; and the ‘top knot’ will be allowed to develop. This Sea Buckthorn is only a young tree, (6 years old) but has the potential to become a Bunjin.
Pruning in general – Heavy Branch Pruning – with trees obtained from nursery sources or from the wild, pruning can be carried out immediately however, with established trees waiting till the autumn to prune is more convenient as the form or shape of the tree, especially with deciduous varieties, can be visualized more easily.
The rules for initial heavy branch pruning are not written in stone, they are more of a guideline. Having decided what the material or plant’s potential may be, one can start work. But before brandishing the shears, a good tip that some bonsai enthusiasts undertake, is to either (a) take a photograph, which can be downloaded to a computer where the style can be enhanced via a suitable program, or (b) draw a sketch of the plant; doing this allows you to finalise the design.
The ‘hand drawn’ image below shows a plant selected to be grown as an informal upright. (Moyogi) Working from the bottom of the tree, a low branch protruding at the front has been removed, as has the opposing branch above it. Further up, the tree has developed a cartwheel effect meaning that more than two branches appear at the same height on the tree; in this case two branches were removed. At the top, the branch on the right had possibly been damaged at some time and rather continuing to grow to the right, had grown across the front of the tree and this was removed. The illustration shows the effect of this initial pruning.
Different styles of bonsai require different forms of heavy pruning, as a general rule dead, damaged, or diseased branches are removed. But with conifers such branches are formed into Jins or Shari, which gives the tree a more aged-look. Jins and Shari are branches that have been stripped of their bark and cambium layer then coated in lime sulphur, which bleaches the branch. With heavy pruning, there will be wounds and these are susceptible to disease, some bonsai enthusiasts advocate the use of expensive cut pastes to seal the wounds, some use petroleum jelly (Vaseline) a fraction of the cost; whilst others do nothing allowing the tree’s natural defences to heal itself.
General Pruning – is carried out throughout the growing season and with most varieties it begins almost immediately they begin putting on the new season’s growth. New growth of all trees can be pinched or removed with the fingers, but if a tree is left until this growth has begun to lignify or harden off, then sharp shears will be required. Pruning is done to maintain and improve the shape and symmetry of the tree and ramification, it is also necessary for the tree’s health.
Leaf pruning – is a method of increasing leaf coverage and fine twig-lets it also assists in reducing leaf size, but it should only be carried out on trees that are healthy and are growing strongly; in some cases more mature trees are less vigorous in their growth for this treatment. June (Depending on the climate zone) is the time when all the leaves except for the petiole (leaf stalk) are removed and after a period of time, approximately 2 to 3 weeks, new leaves and branches will form. However, it should be noted that leaf removal is restricted to deciduous trees, never with conifers, flowering or trees bearing fruit. The above illustration shows how leaf pruning is carried out on pines, junipers, maples and zelkova. (N.B. if you wish to contact us email information is in the ‘about’ section.) Until next time, BW, Nik.