A bonsai is composed of its component roots, trunk, branches, and leaves all of which are integral to its design. The roots and basal trunk are often considered to be the key to achieving a superior bonsai. With poor rootage it is not possible to achieve a great bonsai tree. Following is an attempt to organize some material on bonsai rootage, desirable and undesirable root configurations, and some techniques to improve poor or weak rootage. I refer to roots or rootage in this article as the visible part of the root system. The finer structural roots and hair roots below the soil level are not considered in this article.
General thoughts about Roots
In most bonsai styles a stable root system is necessary and very desirable. By stable rootage we refer to the tree having sufficient number, size and arrangement of roots to complement the bonsai's design and to give the tree a stable appearance in its container. Many root flaws cause the tree to appear unstable and thus likely to "tip over" in its pot. Most bonsai styles have a specific root appearance that seems to augment the tree's character.
Generally roots should taper from their origin on the trunk to their visible termination into the soil. Avoid the chopped-off look that is caused by collecting a tree from the field and chopping its root off at a convenient location. Achieving a nice taper may be accomplished by "feathering" off the severed area along its transition into the soil.
In addition, a tree should have stable rootage. This means that the tree should be endowed with sufficient size, arrangement, and number of roots to help it appear anchored in the soil. A serious deficit in the rootage might cause the tree to appear unstable and, therefore, liable to fall over. Each bonsai style has different rootage requirements that serve to amplify the unique character of that style. Anything that improves the rootage will help to improve the bonsai's image as a "real" tree.
Roots must appear firmly anchored in the soil and have no air spaces visible between the bottom of the root and the soil surface. Exceptions to this are the neagari or exposed root style bonsai, and the banyan or fig tree style, both of which may grow with parts of their roots exposed to the air.
Roots also must flow from the trunk and as with branches, the roots should not curve back to the trunk nor should they be directed straight at the viewer.
To give the tree unity of design, rootage should mimic or mirror the qualities of the tree. For instance a formal upright tree looks best with rather straight roots, while tortuous or snaky roots would be incongruous. On the other hand, a Moyogi or sinuous trunk bonsai should have sinuous or curved rootage.
If possible, roots should also have the same texture as the bark of the basal trunk. A striking variation in bark character suggests the roots were only recently lifted and exposed.
In addition, the size of the roots must be compatible with the trunk diameter. A root's thickness should be about one-sixth to one-eighth the trunk diameter, but always judge the result by what looks best on your tree.
Now that we have some generalities abut rootage under our belts, let's discuss specific bonsai styles and their rootage.
The following is a list of the most common root problems seen in bonsai.
1. Roots at
uneven heights about the soil line.
All too often we have available bonsai material which has a specific root problem. By using various techniques we can salvage all but the most severe of these problem trees.
One, with a tree that has an uneven rootage plane one solution is to remove redundant roots that are not in the proper plane. Another possible solution is to replant the tree on an angle to utilize the staggered rootage. Of course, this will require a readjustment of the tree's apex, depending on the style required and its balance point, figures 17, 18, &19.
Two, a tree with one or two heavy roots can be made more acceptable by splitting the heavy root and wiring both split parts to slightly different quadrants. In this way one heavy root has become two acceptable sized roots figures 20. It will take some time for the cut areas of the root to callous over and to look aged. An overly heavy root may be slimmed down with a cutting tool and brought into proper scale. If the tree's survival is dependent on a large root and therefore unsafe to whittle the root down, a temporary cosmetic correction may be accomplished by a skillful moss application to make the root appear slimmer. Proper mossing can also be used to give chopped-off roots a tapered appearance.
Three, a tree which is too tall or which has an unacceptable or absent root plane can be air layered using the customary techniques to create a new root plane. This works with most deciduous materials but is not possible with most pine trees.
Four, a new root can be created for a tree missing a root by scarifying the trunk, just as for an air layer, placing sphagnum peat around the cuts, and covering with plastic until a new root is formed. Another technique for an absent root is to scarify two faulty trees and place the cambium layers together, figures 21. The trees are wired firmly together for two growing seasons and instead of two one-sided trees you now have a twin trunk tree with good roots all around, figure 22. Or the second tree may be removed in a year or two leaving one tree with a complete root system, figure 23. Another technique can create a very effective visual cure for a missing root by finding an unnecessary branch with the proper bark character and whittling this to appropriate size and shape. This is then carefully placed where needed and mossed into position. I have seen this used so effectively that no one but the perpetrator recognizes the deception. The new "root" will rot with time and will require a more permanent solution.
Five, if you have a large number of trees of one species with poor rootage, it maybe be easiest to use these one sided trees to create a grove planting. Remember that in a grove the roots should not crisscross but radiate outwards as do the spokes of a wheel, figures 10,11.
In this article some general concepts about rootage, and the root requirements of common bonsai styles have been discussed. Several common root problems along with some possible solutions have been discussed. When buying or collecting bonsai it is easier to regrow or retain a tree's top than to correct a faulty root buttress; therefore, it is best to avoid material with serious root problems.