The heat, humidity and long sun exposure of the summer makes it an excellent time for working on tropical bonsai since the trees are growing rapidly and will quickly recover from work. That’s especially important in a display collection such as the one at the National Bonsai and Penjing Museum.
One of my favorite tropicals in the collection is a large banyan style willow leaf ficus (Ficus neriifolia) that has been placed on a slab, giving the effect that the scene was lifted straight of the rainforest. In bonsai, the roots need to be routinely refreshed and we expected the work for the tree to be the somewhat routine work of removing thicker roots to encourage finer ramified roots. However, when we examined the system, we found that the majority of the roots were passing through or around the core of the mound and then the ramified portions were residing along the mound perimeter. This signaled that the core was likely remaining too wet and creating an inhospitable environment for healthy root growth.
In order to rectify this situation, we fully removed the planting from the slab and went to work removing the thick, compacted soil from the mound interior. Clearing this soil makes room for fresh soil. We also removed thicker structural roots that are undesirable for bonsai.
We then used a mixture of sphagnum moss and akadama soil to create a mesh to hold the replacement soil up in the interior of now bare zone, and then filled the open regions with fresh akadama. The mesh wall we created worked well and the soil remained firmly in the interior.
Next came the job lifting the tree and placing it back on the slab in the same position. We started with a base layer of akadama and then lifted the tree into its spot. Many hands make light work when working with trees of this size!
With the tree back in position, it was time to fill in the edges of the mound. We started with the same sphagnum moss/akadama mesh wall to establish the perimeter and filled the entire exterior with fresh akadama. When we were all complete, the mound aesthetic was present once again.
Following this maintenance work the tree is set for a few years of healthy root growth in better conditions. A branch in the apex has died back from the poor root conditions, but luckily ficus develop very quickly and a replacement branch can be grown in comparatively little time.