Bonsai is the artistic cultivation of miniature trees in containers. They are grown and styled to defy time, gravity and perspective. Bonsai is really no more than an illusion that inhabits the intersection of science, art and horticulture. It is an illusion in the sense that the bonsai artist attempts to convince the viewer that the trees are something that they are not. It has been said that bonsai is a paradox: trees are manipulated to make young look old, to make tall look short, to make large look small, to make healthy look tortured and to make otherwise sensible trees appear to defy gravity.
You have seen proportion diagrams of the human body. If pictures of a new baby, a growing child and an adult are all proportioned so that they are the same height, and set next to one another, the head of the baby is much larger in comparison with that of the child or adult. The head of a baby may constitute up to 1/3 to 1/4 of the total length. In an adult, this fraction falls to 1/5 to 1/6. It is this relationship that makes each stage in development so immediately recognizable.
The same is true with trees. Young trees grow long and thin as they stretch to reach above the canopy to the sun. There are fewer branches, and the distance between branches is greater (relatively of course). The ratio between the width of trunk and width of branch is small. Old trees, on the other hand, have remarkable taper. They have thick, expressive trunks that progressively thin through smaller and smaller branches until they explode outwards in a spray of fine branchlets with leaves. Old trees have thick, well-developed roots that often protrude above the ground, and the trees themselves are often gnarled and seemingly tortured by exposure to the elements. If you take a picture of a young tree and a very old tree and scale them to the same size, they look very different, with recognizable differences in trunk girth, shape of the crown, and density of fine branching.
So, back to the original question: “How do you keep bonsai small?” The simple and obvious answer is that you trim them aggressively. You cut the branches back to reduce the distance between buds and to encourage taper and denser, finer growth. This helps to CREATE THE ILLUSION OF A LARGE, OLD TREE. You trim the roots to encourage a fine, dense, healthy root mass with a higher proportion of root hairs to woody roots. By cutting back the top and the bottom, you allow the trunk in the middle to continue to grow and develop, enhancing taper in both directions. By reducing the root mass, you are able to place the trees in ridiculously small pots, further creating the illusion of size and age, and causing the tree to appear to defy gravity. (Although as we know, it is actually wired into the pot to keep it from falling over.)
However, the other, more complicated part of the answer involves nature vs. nurture. By forcing the tree to deal with limiting conditions, the tree learns to develop new ways of coping: growing smaller leaves, reconstituting its root mass, throwing out new branches where none existed before, adapting to new nutrient supplies. In essence, we convince the tree that it can make a better living as a small tree than as a large one. In so doing, we create large, old trees out of little, much younger ones, and we keep our old trees small.
So bonsai enthusiasts: the next time someone asks you how you keep your trees so small, look thoughtful and reply: “I don’t keep my trees small. They do it themselves.” Then smile and change the subject.
Let’s keep the illusion and the paradox intact. [.]