I have spent most of the year so far bitching about not re-potting bonsai or at least not re-potting too often. The whole notion of Bonsai trees and free draining soil seems to be one of the top mis-understood aspects of bonsai tree cultivation but I’ll save that for another day. Why we actually re-pot bonsai and when that should be done, by and large, seems to be deeply immersed in ignorance. However what we call bonsai trees and their long term maintenance and the situation with trees in development towards becoming bonsai are two entirely different things.
Where development of bonsai is concerned, the most important aspect is that of developing a ‘bonsai’ root system. By that I mean a pot full of fine dynamic feeder root mass largely free of big chunks of wood or old mountain or field soil. Anyone who has re-potted an old Japanese bonsai tree will be familiar with this. Developing such a root system can be very easy with something like an elm or maple but in the case of evergreen varieties and in particular pines I regularly see folk struggling. Trouble is most of what is written about re-potting pines is based on working with existing bonsai trees. Working with yamadori seems to scare a lot of people in my experience.
Simple rules apply here. Never mess with the roots of a tree that is not showing strong growth and annually improving vigour. If you have not owned the tree long enough to do this or cannot read the signs wait until you have or can. Secondly never work on the roots of pines that are dormant. Fast swelling buds and thick fleshy white root ends are good indicators if working in spring. Summer re-potting is also a good prospect particularly with European natives like scots and mugo pines.
Root work for yamadori such as this big scots involves the complete removal of old mountain soil. This is an important step in order to develop that valuable ‘bonsai’ root system. Many folk go white at the prospect but in my experience a pine will never grow properly in a small pot OR develop that root system until this is done. Where first root work with yamadori is concerned simply allow the soil to dry out prior to beginning work. Then patiently pick out all the old soil right back to the trunk. NEVER wash the roots at this stage unless you really want to kill your tree. Then all that is required is to cut out as much thick wood as is possible and shorten large thick roots where they exist, cut back to where roots emerge closer to the trunk. Be patient, this is going to be as long process and this shortening MAY have to be done in several stages. Finally gather up ALL the root and put it into a suitable sized pot and work it into a suitable soil mix.
This work will increase a pines growth rate, make larger needles and more back budding very quickly. All important factors in pushing a pine tree down the bonsai road. Subsequent potting can focus more on root pruning for development of fine root mass and having cleaned out the old soil completely this becomes the work of minutes rather than hours as in the case of this beast I did yesterday.
Folk often ask me about mycelium in relation to pines. In my opinion those of us who keep pines do not actually keep pine trees we keep their mycelium. If that fungi is happy your pine will be happy. If a pine tree has no fungi present chances are the root system is too wet or full of junk not conducive to it’s well being. In the case of this tree the original mountain soil was largely devoid of hyphae but the pumice and perlite around that was solidified by a huge mass of hyphae. Now that the growing medium is consistent and correct mycelium will colonise the ENTIRE root ball. Seeding mycelium is not necessary, creating a good environment for it to thrive absolutely is.
Few things in bonsai are as simple as the cultivation of pine trees. Sadly few things are less understood in bonsai that the cultivation of pine trees.