Bonsai Studies in Japan: Part 2 by David Johnson Group and Rock Slab Plantings The article Repotting Bonsai in Japan in the March 2003 issue of The Journal began this series and forms the foundation for the articles that follow. Of the many trees I repotted at Mr. Nakamura's Shonan School of Bonsai, group and rock slab plantings need a more detailed explanation. Group Plantings Mr. Nakamura repotted a number of group plantings. The trees in all of the group plantings were removed and then individually root and branch pruned. Often the group plantings were re-designed by re-arranging the placement of the trees. None of the trees were wired in. I was surprised to see this since all of the group plantings I have seen in North America have the trees wired in. Mr. Nakamura root pruned the root ball flat so that the tree would stand on its own. When I asked Mr. Nakamura about the lack of wire, he said that muck (a combination of rice field soil, Akadama soil and water) could be used to stabilize the trees. A small trowel was used to press the soil down to firm up the planting. Mr. Nakamura often pruned the roots so that two trees could be potted closer together.

Group planting done by one of Mr. Nakamura's many students. Note placement of trees and cut-up sphagnum moss on top.

After I tried my hand at repotting a group planting, Mr. Nakamura suggested I read an article in Bonsai Clubs International's magazine, Bonsai - March/April 2002 on forest plantings. He said I needed to create more space between and around the trees. The article, based on a group planting demonstration done by Mr. Nakamura in the United States, outlined four don'ts and four do's: Don't plant the container full of trees (leave open space); don't plant more than three trees in one line; don't plant trees with same thickness and height together; and don't plant trees the same distance apart. Do plan ahead; do prepare trees with various sizes; do place taller trees in front and shorter trees in back; and when finished, do place planting in full sun but away from the wind. When Mr. Nakamura worked on group plantings, he planted smaller trees near the back to give a sense of depth, larger ones in the middle and the medium ones toward the front. On the outer edges the smaller trees leaned outward. He placed one-inch pieces of cut sphagnum moss on top of the finished replanting to protect the surface roots (forest planting pots are shallow to match the narrow diameter of the trunks) and prevent the soil from splashing and washing away.

Another student's group planting.

After reading the article, I arranged the shorter trees at the back of the group planting in an arching rainbow fashion but it did not look good. With the help of Mr. Haruo Nakamura, Mr. Nakamura's brother, I re-arranged the trees at uneven heights. The planting's movement (to left or right) was established by the largest tree. Rock Slab Plantings Mr. Nakamura broke up a fifteen-year-old mixed rock slab group planting of Japanese black pine (pinus thunbergii) and Japanese hornbeam (carpinus japonica) for repotting. This planting had been repotted once before but the roots and soil had become hard as a brick. The trees were removed from the old rock slab, divided individually and given a severe root pruning. I repotted a hornbeam with bark ripped off at the base in a training pot but not deep enough to cover the damage. Sphagnum moss was applied to cover the damaged area. All of the individual trees were immersed in water as we worked on other trees in the group. Mr. Nakamura brought three young pines and two- and three-maple (acer palmatum) groups to be added to the final planting if needed. While Mr. Nakamura worked on a forest design, I re-wired the new rock because many of the wires were too short. I wired in longer tails that could be used to tie down other trees. The rock looked natural but was actually artificial with drilled holes. Mr. Nakamura divided a group of three maples. I held two pines in place on the slab while Mr. Nakamura added some soil to stabilize them. He then tied the trees in with wire. A non-flowering azalea was added as an accent plant which is used sometimes with mixed plantings. We did more tying in, added more damp soil, then more tying in and then more soil. A potting stick worked the soil into the root balls. To finish the repotting, a muck wall was built around the planting. Mr. Nakamura made the muck by mixing rice field soil, Akadama and water until it had a sticky, stiff consistency. I shaped the muck into "sausages" about four to six inches long with a one-inch diameter. Mr. Nakamura placed the "sausages" around the soil mass and then squeezed inward. Moss was placed firmly on the sides and top of the wall and on the soil. Mr. Nakamura preferred to work the soil into the roots of the planting before building the wall because it was easier to do at this point. The planting was watered in the centre of the soil area, avoiding the muck wall. The finished rock slab planting was put in a greenhouse and not watered for two or three days. The greenhouse protection and the semi-shade conditions may have been due to the cool weather coupled with the early transplanting of pines. (Unfortunately I don't have a photo of this planting. I don't remember if the maples were added.) Pinus Parviflora Rock Slab Planting Another rock slab planting we worked on was a pinus parviflora root connected clump. Mr. Nakamura wanted to repot it on a larger slab on which he had glued some wires a week earlier.

Pinus parviflora clump before work began.

The chalk line in the photo shows placement of the clump. Mr. Nakamura said the selection of the front of the slab is important and it should have the edge move inward and then out again.

New rock slab viewing it from the back.

For this planting Mr. Nakamura built the muck wall first. After the wall was built, he added some soil to the bottom. Mr. Nakamura removed the group of pinus parviflora from the original slab and did some heavy root pruning. He used a pair of large root cutters on the larger tree base to flatten the root ball and make it sit better. Some of the original accent plants were removed but the Japanese quince (Chaenomeles japonica) was reused. We positioned the clump, added soil and then wired it in. Mr. Nakamura told me not to break the wire because it was glued to the rock and not easily replaced. I started twisting the wire at a bad angle and broke it. Mr. Nakamura twisted an extension on to the end of the broken wire. We added more soil and worked it in with the potting stick. Moss was added to the wall from the bottom up and then on top of the entire planting. The moss was pushed in firmly on the walls but only pressed down lightly on top. Mr. Nakamura said to do this many times. The pinus parviflora rock slab planting also went into the greenhouse.

Finished rock slab planting.

Mr. Makoto Nakamura, Mr. Nakamura's son, repotted a nice trident maple (acer buergerianum) root over rock planting. He used heavy wires to hold down the rock/tree until new roots could stabilize it. Later on during the growing season, the wires would be removed.

Root over rock being temporarily stabilized with heavy wires.