For our January 2017 meeting BSSF kicked off the year by inviting Bernard Marque, a long-time BSSF member to demonstrate repotting for the group. Bernard has recently taken over the helm in teaching bonsai basics II for the club which is the repotting portion of bonsai basics.
Bernard began the evening by mentioning some of the general reasons and parameters for repotting. “Every time you touch a tree it is an opportunity to improve the tree, whether you are repotting or trimming” You can improve the health of the tree by repotting, but you can also improve the aesthetics through the repotting process.
Bernard related a story about the plant pathology staff at UC Davis indicating that bonsai soil is not likely to be good for trees. After he did an emergency repotting in September to remove a tree from a very shallow shohin pot Bernard took the tree to Davis and was surprised to find no fungal problems causing his tree to be sick. Instead, it seemed to be a root problem that needed to be corrected, perhaps caused by a lack of repotting the year prior.
While talking, Bernard and Liep screened the hexagonal pot in advance of removing the juniper from it’s old container. They used 2.0 aluminum wire to provide tie-downs for the tree. There was a discussion of soil characteristics mixed in: drier soil mixes, like those containing less organic material or akadama, will promote faster root growth and hence more coarse growth on the top of the tree. Finer soil that retains more moisture will typically promote slower root growth and is considered to be better for trees that are established bonsai.
Repotting can take quite a bit of time in some cases, at the minimum 20-30 minutes, but often 2-3 hours can be spent properly combing out the roots and getting them into the new container. The amount of time needed will depend on the condition of the rootball; trees that have not been repotted frequently, or that are coming from nurseries will typically require a lot of exploration and trimming. Trees that are established as bonsai will frequently already have an orderly root ball. Particularly for deciduous trees care should be taken to comb out and arrange the roots where possible. Over time, proper root trimming will greatly enhance the nebari on many species of trees.
When you remove the tree from the container you will normally find the greatest amount of root growth on the bottom of the container and along the sides. Bernard trimmed off the matt of roots on the bottom first. When questioned about the working sequence he mentioned that he always starts with the bottom, then does the sides and then combs out the top. Bernard emphasized that the laterally growing roots from the trunk will be retained for the health of the tree.
Bernard remarked that the root mass of his demonstration juniper, which had been growing in the same container for 7 years without repotting was actually less dense than he expected. In the case of the juniper demonstration tree,the surface roots were already visible in the container. The tree was grown from a small cutting in the container into a plant that has more than a 1″ trunk in that time.
The work revealed that a lot of the roots were tangled up and long, likely the result of the long repotting interval. The trimmed roots will now have a smaller space to grow, but the process of trimming them will cause a more dense rootball of finer structure that is well-suited to a bonsai container.
Look for more advice from Bernard on repotting at one of the repotting workshops or a 3rd Thursday session.