These are two ocean eroded lava rocks with interesting surface textures.  If a tree was planted between and the roots filled the gap between the two rocks,  it may appear to be a single rock. You can hold the rocks in the proper relationship to each other by placing newspaper between and taping the rocks together tightly so you can lift up both and set them down onto a "concrete pancake."  That's the basic idea, but I added two more rocks and used an 18" diameter aluminum party platter as a form. The bottom was perched onto a low sand hill and three "legs" in the sand will lift the slab so water can drain out below it.


                  This idea began to show that two rocks can be held together at the base with concrete so you could plant a bonsai between them and the arrangement could look like it's a single rock with a tree on it (even though it's really between the two rocks).  Here's how it was done.




           First two rocks were separated with newspaper and tightly held with monofilament tape.  Another rock was added with newspaper between and also held with monofilament tape so it could be lifted up as a unit.  A fourth rock would add contrast and interest.



           Fine screened lava sand that went through a 1/8" screen and caught in a 1/16" screen with the dust that was allowed to fall through discarded.  Dampen with sprayed water, shape a slight hill in the center, and make three 3/4" diameter depressions about equal distance to become the "tripod legs" to lift the slab above so any water would not collect below the slab and drain out if the slab was placed inside a wide pot. 



            Cover the sand with clear kitchen plastic wrap.  We use Quickcrete with the aggregate screened out and added black coloring.  Mix cement and first fill the three depressions that will be the tripod legs.  I did not want a thick heavy slab and this first test was based upon a 1/2" thickness form most of the slab with it being heavier where rocks were placed. 



             When the entire surface was covered about 1/2" thick, another 1/2" was added where the rocks would be placed and the rocks lowered and positioned into the wet concrete and snuggled down for good contact.  Small rocks were wedged down between the rocks to force cement up against the rocks. Wet cement was tooled up against the bottom 1/2" of the exposed rocks to assure binding. 



              I screened rock chips through a 1/2" screen and what was caught in 1/8" screen was used along the edges and next to the rocks.  The finer dust was sprinkled wherever the cement was shiny wet.  This will give the slab a more natural coloring and will encourage moss to grow if grown outdoors. 




               U-shaped anchors were set where tie-downs would be needed and the slab was allowed to dry for two days. 

              A second smaller slab was made with the leftover cement. Being smaller with a smaller stone, it was planned to be jus 1/4" thick.




              A 12" diameter shallow saucer was used as the form with a small sand mound formed with dampened sand, three leg depressions made, and the surface covered with clear kitchen plastic wrap.




             Cement was spooned into the leg depressions first, then in a roundish but irregular shape not reaching the sides of the saucer.  Some finer rock scrap was sprinkled in one section about 2" wide.



             Additional cement overlapped the rock scrap area and more rock scrap sprinkled on.  Another cement layer was added, and after assuring that the cement was in good contact with all edges of the rock, more rock scrap and dust was sprinkled on the entire surface. 



             The rock has three saddles and I'll likely plant three plants on it to make a nice small landscaped hill. We've made several trials of this smaller size so am very confident it works.  The next day I lifted the rock, peeled off the clear plastic and set it aside to plant in the future.  The larger 18" multi-rock unit was given another day to harden.  



           This second slab was also lifted up by the rocks and came free of the party platter with no problem.  It will tilted up, held with one hand, and the clear plastic wrap peeled off without incident.  The rock scrap and dust that did not stick to the wet cement was brushed off.



          This shows the bottom with the three tripod leg supports.  There's an extra bump as I had pressed down on the rock to make sure there was good contact. But the slab sits on the three tripod legs and is steady and water does not collect under the slab. 



           The slab after it was washed down.  It will be allowed to cure until I have time to plant it.  I'm thinking of putting a larger older Roots bonsai that is about 16" tall and 16" wide on the slab.  It will be nice from the start.  There will be an option to place this entire unit into a low larger shallow bonsai pot to provide more potting media for a more vigorously growing bonsai.

   TO BE CONTINUED  .  .  . 

January 20, 2014  ~~~DWF


            Two days later I was ready to plant.  But the smaller trial was sitting in water and the cement didn't cure so the bottom broke!



             The cement was just 1/4" thick with the leg another 1/4".  So more of the slab was broken off with a pliers and the unit fitted into a 9" diameter 1:10 Project saucer with a lot of drain holes. The legs keep the slab from blocking the drainage and because the rock has three saddles, I may plant 3 small plants on it in the future.  But today I wanted to see if the 18" diameter multi-rock arrangement would work without a pot.




              First I used a broken piece of a hollow tile to knock off the sharp outer edges.



             I selected a tree that was part of an Advanced Workshop III - Roots that up-potted an 8LS8-Roots into a larger #17 Conversion kit to create a larger longer extended roots bonsai.  That workshop as done about a year ago and I knew the roots were long enough, but that it was still not overly full of roots. The tree was bare-rooted.



              I guessed right that a few of the roots were long enough with most of the well formed roots still on the upper section and the plant was at an ideal stage for the planting it within the cavity formed by the four rocks that was tied together with the concrete base.


              The space between the first two rocks is a little more than an inch wide.  But it was about 3"-4" deep. Only two larger roots would be in the space on the outer edge so there's a lot of room for potting media for the tree to really grow vigorously.  But if the planting is done correctly,  it will have the appearance of a single large rock and that no one will realize that there is a large amount of media between the rocks!



             From the other side, the space between the second and third rock is much wider to be able to hold a lot more potting media!  There's a lot of daylight between the first two rocks and I estimated that I'd be using between 1/2 to 1 full gallon of potting media although very few would guess that much was used.



           For this type of work,  a piece of sheet iron was cut and shaped into an "open-top funnel" and with a dibble, it was easy to position a lot of potting media in a short time.  First coarse bottom went in to provide good drainage, then nutrient granules, more coarse bottom, body media, more nutrient granules, and more body media until filled.


           A temporary paper covered bindwire tie kept the two roots even with the face of the two rocks and using the open top funnel, a lot of coarse bottom, nutrient granules, and body mix went in between the roots.  As it came spilling out,  damp sphagum moss was filled between,  the media dibbled firmly into position, and more sphagnum moss filling the voids from the bottom up until all was done on this side and this continued on the other side.  Tie wires attached to the U-shaped anchors were used to secure the tree.


           This is an overall view of the side that shows the first two rocks with the two roots in the space between the two rocks.  As the roots thicken and fill that space fully with roots,  it will increasingly present an illusion that the tree is sitting on a single large rock formation.  Because there is so much potting media within the rock,  the ends of the roots were tucked into that mass and most of the exposed slab will have just a small amount of fine media that will quickly be colonized by hair roots to keep it in place.  No other pot is needed.


             This close view shows the area with the most potting media that contains the bulk of the roots including some free-falling aerial roots.  The small flattish rock provides a nice contrast and helps support part of the media.  In this area,  a number of bonsai wires are going up and down and there are several diagonal paper covered bindwires forming a grid and network to hold the roots.  Media is inserted and dibbled firmly behind the roots and the wires prevent the roots from bulging out. 


              A third close view showing the planting area between the largest first rock and the third rock with one large root even with the rock edges.  Note that a bonsai wire was secured around the base of the rocks and this allowed any number of vertical wires to anchor down the tree and form the vertical portions of the grid and network that secures the roots in place.  After this photo was taken, a small amount of organic rich fine potting media formed a transitional slope to the base of the rock and once hair roots form, it will stay in place and not be washed away when watering. 


               An aluminum foil collar was installed to protect the root trails until the potting media firmed up and hair roots developed to hold it in position.  The foil was curved under the round concrete slab.  It will likely stay in place for six months to a year with portions being removed a little at a time,  uncovering the top portions first and removing more as the roots hold the media in position.  The tree will be severely cut back to create a smaller crown to match the size of the slab.

              SOME FINAL THOUGHTS.  When I began bonsai in the 1962,  ceramic bonsai pots were considered expensive and most of us were training trees in food cans that had low walls with holes punched into the bottom for drainage.  In those days,  tuna cans were a bit larger and the favorite for creating small bonsai.  Bonsai pots were made with "dry mix cement" that was compacted in metal molds.  They were all rectangular and came is a few different sizes and they were the first upgrade from bonsai grown in cans.  But over the years, the standard were raised and to exhibit your plants, it had to be in a ceramic bonsai pot.

              Haruo "Papa" Kaneshiro was one of the few who could afford the highest quality Yamaaki pots made by the Kataoka family in Tokoname, Japan.  Papa had visited the factory and the family had given him a special tour.  The master potter Akiji Kataoka was the first to equal the quality of the Chinese Yixing pots in the 1920's.  He began to create original Japanese pots utilizing clay slabs hand pressed into molds and burnished but not glazed.  Papa shared the fine points of how to evaluate the quality of Japanese pottery.

              Japan had a modest economic level in those days and in comparison, those of us in Hawaii were considered "rich" by their standards.  Hawaii was then amongst the largest overseas "export market" for bonsai pots and I'm told that Honolulu's Kamioka family that ran Standard Trading Company became the largest buyer of Japan bonsai pots. Most of the pots that were imported were the highest quality grade from Kataoka's Yamaaki kiln.  Much of the highest quality of Japanese bonsai pottery produced before the "bonsai boom" prior to 1970 were sent to Hawaii.   

                I recall that on a club bus trip in the late 1960's to see the bonsai collections in Wahiawa, that I first saw bonsai growing on concrete slabs.  Wahiawa is cooler at a higher elevation with more rain and moss grew well and the landscapes were very attractive.  So I've been dabbling and making concrete pots and slabs for many years.  In the early 1970's I dabbled in making ceramic pots and even learned how to carve Plaster of Paris models and to make molds.  Potters tend to do some of their finest work by throwing on wheels and perhaps that's why I like round pots.

                I also liked Papa's definition that a "bonsai's front" is the side facing you and that bonsai should be created to be attractive from all views.  If so,  round pots were better.  As I became committed to houseplant bonsai, it was necessary to keep turning them to grow evenly as most light from windows is directional and if not turned, it would grow towards the light.  We've been planting large bonsai on round concrete discs since the 1990's and the Entry Tree is on a 6' diameter slab!

                So it was an interesting challenge to scale down to an 18" diameter slab and as I have time, I'll try to do more of them!  Hope you found the report interesting and that members of the study group keep improving the concepts!    ~~~David  (

*** Return to the February issue of the Journal of Tropical & True Indoor Bonsai
*** Go to Mid-Pacific Bonsai Foundation website
*** Go to Fuku-Bonsai website
Mid-Pacific Bonsai Foundation and Fuku-Bonsai, 2014