Root-Over-Rock Salvage Operation

By Dierk N.

You may recall that during the ice storm of Dec. 2013, my greenhouse was without power for several days, with the resulting loss of most of my tropical bonsai. Some of the “larger trunk” ones are showing slow signs of recovery, and so there is indeed hope that trees may be salvaged, somewhat, and regrown over the next few years. One of the victims of the cold was a ficus retusa that, years ago, was made to grow over a rock, though a rather small one – after several years the rock was no longer visible as the tree had completely covered it with its roots and trunk.

Since then, I have always wanted to try my hand at another root-over-rock creation, but this time with a much larger rock. I found that rock during the recent mild spell; it was a piece of granite from the Parry Sound area. With the help of some silicone seal I glued the rock to the base of a ceramic bonsai tray, making sure that the rock could in the future be moved to new quarters.

What I lacked was suitable plant material. I decided that I did have a possible, recovering candidate (shown) in the greenhouse, that was starting to show signs of life again near its base; what was left of the original tree had a trunk of about 2” in diameter. When I pulled the tree out of its pot I discovered that it actually had a few more inches of trunk available, once a few roots were trimmed off. This tree was my choice for this new project; it is a strangler fig and should be a good choice for this type of bonsai.

The first thing to be done was to remove and wash off all of the soil from the roots of the tree, remove other roots that had died during the cold snap in December, and then see how the tree might “sit” on the rock. It quickly became clear that numerous roots were going to be an issue since they were quite large and not very flexible, and sticking out at rakish angles from the trunk. Some of these would need to be removed to make the tree fit the rock, but others would have to remain to maintain the viability of the plant material.

Other awkward roots could be trimmed in the future once the tree had settled into its new environment – this settling in would probably take at least a year. Fortunately all of the roots were long enough that they would go right down into the bottom of the bonsai pot.After trying several possible poses on the rock, and making sure that the tree would not sit at the very top of the rock and, therefore, look unnatural, I settled on a position and began the process of planting the tree. To begin with, I used some raffia that had been soaking in water overnight. The first objective was to tie the rock to the tree; the second was to tie the roots as tightly as possible to the rock. The advantage of using raffia is that over time it will rot and will not leave unsightly marks on the bark or roots. During this operation it was also critical to keep the root system moist with frequent misting.

Since the tree and roots were quite high out of the pot, the next issue was to find a way of positioning soil around the tree and rock to encourage root development to continue. Fortunately I found some heavy duty plastic covered bristol board that I wrapped around tree and rock and positioned all of the way down in the planter. This material would allow me to place soil around the roots, and over the next year or two, gradually remove strips from the top in order to expose part of the root system to air.

Once the plastic covered wrapper was in place, the process of “potting up” continued.First, some rooting hormone was sprinkled over the roots to encourage root formation and growth. Then some sheep compost was placed at the bottom of the arrangement; this was covered with a good amount of peat moss rich potting material that would hold moisture around the roots and trunk that were above the bonsai tray. Finally the pot itself and the top of the rock section were covered with well draining bonsai soil made up of granite, black earth and diatomite. The last step in the process was to give the whole arrangement a good application of water to wet the soil and help it to settle around the roots.

Now it is time to wait. I hope that not too much new stress was placed on the tree, and that it will recover and continue to grow. Since most of the tree had originally been killed off by the cold snap, a whole new branch and trunk system will need to be developed over the next few years. Gradually strips of the plastic paper covering will be cut off so that roots become exposed to air and develop natural looking bark. The jagged remains of the old trunk will be trimmed to look a little more natural.