Decandling a Japanese Black Pine is one of the techniques that allows for long-term containment of mature bonsai and establishment of younger trees as bonsai. While the process of removing all the spring growth is well documented across multiple successful techniques, there is little documentation on whether or not to fully or partially decandle a black pine. This is largely because so much of our education on bonsai comes from reading articles originally published in Japan or heavily influenced by Japanese bonsai, and much of that information is aimed squarely at trees that are actually quite rare in the United States. How many full Japanese Black Pine were in the last exhibit that you visited in the U.S.?
Most Black Pine in the U.S. are in development stages so thorough decandling every year is not always the right answer if you desire the most expeditious development. Analyzing your goals for a particular tree will inform your decisions on whether or not to decandle the tree. For trees that are in development ask yourself – will decandling further your design goals? Or will it just slow down the process of getting the tree to maturity? Selectively not decandling can encourage weaker branches to become the stronger parts of the tree. Any branch on an established mature specimen that begins to weaken can be left to grow while the other branches are decandled in summer. Selected branches on trees in development can be left to grow to create branch or trunk extensions or to increase the vigor of a particular part of the tree. Use a balance of critical thinking and horticultural analysis to help in your decisions. Here are some examples of decandling decisions I've made.
Another nine-year-old pine – last year this tree was decandled behind the nodes to push needle buds so that the tree would be more compact. This year I left one bud at the top center to run, it will create the center of the new top. Two or three years of not decandling this branch will allow for a small trunk extension.
A third nine-year-old pine. I left two buds at the top of this one to help establish the upper trunk line; right now the structure is missing for a good top.
A small older pine – completely decandled except for some weaker buds on the interior of the pads. These buds would die if decandled but may now end up too large and strong to keep. Since the pads are already dense they can be eliminated in the fall if they don’t work for the design.