Article 89 – ‘Design: a discussion’ Part 8

Hi welcome to Taiga Bonzai, in this article the last in the discussion on design, we look at the examples of ‘root over rock’ – Sekijoju where the root system encompasses the rock and Ishizuki – ‘root clinging to a rock’.

Disclaimer notice: – this article is not a tutorial on how to produce these two designs, it is a brief explanation on the process of how they are achieved. This art requires certain skills that have been omitted due to their complexity, we are not responsible for any actions taken by others.

Introduction Sekijoju and Ishizuki do take time to construct in order to achieve a balanced composition between the two components tree and rock. Arguably the first step is to decide which to opt for Sekijoju or Ishizuki and to jog your memory Sekijoju is ideal for deciduous varieties as they grow more quickly than conifers, whilst coniferous species can be adapted to both styles. We will use the Ishizuki style for this discussion.

Sekijoju and Ishizuki

Coniferous or deciduous – having made the decision on the species, one has to ascertain it’s possible potential and growth rate, hence a little time spent researching the chosen specimen the better the knowledge. The most important factor at this stage is the size of the root ball, short fat root systems as found on slow growing varieties should be avoided for obvious reasons. The roots need to be robust and extensive more than the total height of the tree; if the chosen specimen does not meet the required measurements, it can be replanted in a deeper pot for a season or two.

So which tree species are suitable, there are many to choose from for example, deciduous can include Ficus aurea, Ficus benghalensis commonly known as the ‘strangler’ fig and banyan tree respectfully as these have extensive aerial root systems that extend to the soil. Others are hawthorn Crataegus, birch Betula nana and cotoneaster family Rosaceae. With conifers these can be juniper varieties of which there are between 50 and 67 to choose from, they include the common juniper J. communis, J. chinensis and J. virginiana.

Whatever the species, the root ball is checked as is it’s configuration a sketch or photograph is is made which is useful when selecting the rock. The distance between the primary and secondary roots is measured, their thickness and pliability especially where they protrude from the base of the tree. This information is written down because it is needed when carving the rock, more time spent on this part of the project reduces the risk of errors later on. When the task is completed, the roots are misted with water and the tree is returned to it’s pot.

Rock choice – there are three main types of rocks igneoussedimentary and metamorphic that are formed by physical changes which include melting, cooling, eroding, compacting or deforming. Common examples are obsidian, granite, pumice, porphyry, calico (laminated sandstone) coquina, (shell limestone) breccia, gneiss, talc schist and serpentine to name but a few of the many that exist. All have different degrees of density, obsidian is soft but prone to fracturing and the shards are extremely sharp. Granite is hard and can be difficult to carve whereas pumice being light weight is easier, see Gaby Pilson’s article on rock types link below.

30 Types of Rock That You Shouldn’t Take For Granite: Pictures and Facts

Carmichael, Robert S. and Klein, Cornelis. “rock”. Encyclopedia Britannica, 19 Oct. 2022, Accessed 5 December 2022.

The hardness of the above rocks as recorded on the Mohs scale of hardness with the number 10 being the hardest are listed here in the order that they are shown. Obsidian 5 – 5.5 – Porphyry – 6 – 7 – Calico (laminated sandstone) 6 – 7 – Coquina (shell limestone) 2 – 4 – Breccia 3 – 6 – Gneiss 6 – 7 – Talc schist 4 – 5 – Serpentine 3 – 6. Others (not shown) include Granite 6 – 7 – Pumice 6 – 6.5 – Quartzite 7 and Slate 2.5 – 4. Before embarking on a rock hunt it would be prudent to research the types of rock that are common in your area, if their appearance does not satisfy the needs then one has to look further afield.

Rock preparation – once the rock candidate is found it has to be prepared by using warm water only, cleaning agents or other chemicals are to be avoided. The rock now has to be sterilized using boiling water for 30 minutes in a clean receptacle in which the rock is submerged. Eye protection is needed as some types of rock are prone to spitting when they break, do not take shortcuts by boiling the rock on the stove because it may explode.

Starting at the rock’s surface (where the tree sits) the root positions are marked out using a permanent marker, the thickness of the roots is checked and depth is noted. This is important because the roots have to just sit in a channel a few millimetres deep no deeper, this is to give the viewer the impression of a natural phenomenon. If this is not done the tree will not correctly fit when anchored down, there should be no gaps between the tree’s base and rock surface.

The trajectory of both primary and secondary roots are marked out, the process is repeated until all the required roots have been marked out. Excessive roots can be removed especially those that interfere or crossover other roots. But not too many as the tree relies on its root system for moisture transportation and sugar reception produced by the foliage. The rock should now resemble a road map full of lines around itself when completed time to begin carving.

The tool needed for this is a Dremel equipped with cutting discs, grinding stones, eye protection and gloves. The Dremel has variable speed and when in motion can cut into the rock with ease depending on the rock’s density, but it can also cut through gloves and fingers; hence a comfortable speed setting is advisable. Carving rocks has its moments, but it is time consuming holding the piece in one hand whilst carving with the other and is often done in stages. Below is an image of our Dremel equipment.

The rock now completed is washed to remove any dust, the channels are inspected for any imperfections and removed if needed. The rock is turned upside down and two wires are fixed to the surface using epoxy resin, these are there to anchor it in it’s intended final ceramic pot. When dry the wires are folded back on themselves so they do not interfere with root growth. Time to marry tree and rock together, plain rafia (not coloured) is needed soaked in tepid water then unravelled. Strands are gathered together and are smoothed out and a knot is tied at one end, the strands are used for binding the roots to the rock.

The tree now out from its container has the soil removed and with the aid of the sketch/photograph the roots are now fitted into the channels, starting at the top working around and down occasionally misting both roots and rock. Wet rafia is tied around the rock to keep the roots in place. Once the task is completed the whole rock is bound again starting at the top working to its base, the rafia is then securely tied.

Grit for drainage is placed in a clean old plastic bucket or wooden box (must have drainage holes) add fresh soil and that which was removed from the tree and it’s container, fertilizer is sprinkled on the medium. (we use granulated pellets) The tree/rock combination is planted just below surface level, watered and left to recover; 2 – 4 years (deciduous) and 3 – 5 years (coniferous) depending on the species.

The approach and methodology in producing the Sekijoju and Ishizuki design discussed here is but one way, other designers will have their own way of producing the same result. And yes we do agree that to venture on an art form such as this takes considerable time, but that is the nature of bonsai or in this case Bonkei. A never ending study of the world’s oldest ‘living’ art form where complicated designs take considerable time to produce, if we are to present a piece of ‘live’ art that is natural in its appearance.

Having read this article there will obviously be a lot of questions regarding these two designs Sekijoju and Ishizuki and we will answer some of them here, you can send us an email ( where you will receive a detailed answer or simply add a comment on our website.

Q. If the Sekijoju style is chosen is there much rock carving to be done if we use the ficus types mentioned or similar species? A. Regardless of the species it is advisable to carve channels to direct the roots in the path you wish them to take.

Q. Can tufa rock be used for these styles? A. Tufa a highly porous sedimentary rock is composed of calcium carbonate, CaCO3 (Limestone) its texture is rough, uneven and full of holes. Although it is not a rock type that we would recommend, there are no rules to say it cannot be used.

Q. Instead of burying the finished piece in a bucket, why not put it straight into its ceramic pot? A. The sculpture will eventually be housed in a shallow pot beit rectangular, oval or round where root run is confined. As the tree has undergone pruning it needs to develop a strong healthy root system therefore, it will develop more quickly in a deeper pot.

Q. Why is the timeline so long? A. Much depends on a tree’s natural growth rate, as stated in the main deciduous develop more quickly than coniferous species, but having said this each particular type of tree beit deciduous or coniferous will have its own growth rate agenda.

Q. Some of the rock types shown are interesting yet a bit too colourful what is the best rock type to use? A. What you are trying to create is an art sculpture that has a natural look a balance between the three entities, tree, rock and pot colour. Porphyry, calico and pumice are fine for deciduous where as granite and pumice are suited to conifer varieties, but you can use whatever you like there are no hard rules.

This concludes the series Design: a discussion, if you wish to attempt these designs we are available to assist, but please remember bonsai requires patience; until next time, BW, Nik.