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The roots

We take it for granted that all plants have roots of one kind or another, but if we’re going to be responsible for keeping a tree alive and in the best of health, it is essential that we understand a little more about them.

The function of roots: Roots have three primary functions. The first is, quite simply, to stop a tree from falling over. The roots that spread out from the base of the trunk extend in all directions, anchoring the tree in the soil. This applies equally to bonsai. If a bonsai is easily rocked in its pot, then the roots are failing and, if the roots are weak, the tree will also be weak.

A thick taproot and a mesh of finer side roots on a young plant. The taproot is the first root to develop on a seedling; it provides anchorage and seeks moisture.

The second function of roots is to draw nutrients and water from the soil. Species that are adapted to grow in arid regions have long, searching roots which tap moisture from a wide area.

Others that live in moist, fertile soil have fine, shallow roots that may not extend beyond the spread of branches. A tree living in the confines of a bonsai pot must have a well-developed, efficient root system to stay healthy.

The third function of the roots is to act as a pantry for the tree. During the dormant season the roots store sugars that were manufactured by the leaves throughout the summer months. The storage areas are in the heavy, woody roots, so it is vital to develop and preserve an adequate number of these sturdy roots on your bonsai.

How roots work: If you examine the roots of a tree or shrub, even on a small nursery plant, you’ll notice that there is no taproot. The taproot is the first root produced by a seedling; it grows directly downward to seek out moisture while it provides stability. People used to think that the taproot continued to extend downward for a considerable distance, but that is now known not to be the case.

Roots will only grow down as deeply as they need to locate a constant supply of water; and, in most cases, that is not very deep.

It is worth noting that the roots are structured rather like the branches; the thickest roots radiate outwards from the base of the trunk, they then fork regularly and terminate in masses of fine roots at the tips. In a full-sized tree, these fine feeding roots may be located way beyond the outer reaches of the branches and cover a massive area.

In a bonsai tree, however, the roots don’t have the luxury of wide open spaces. They must be super-efficient and able to gather all that the tree requires to keep it in good health from a relatively small volume of soil. To do this effectively, the majority of the roots should be encouraged to become very fine and dense in close proximity to the trunk.

Moisture is drawn into the plant for absorption by osmosis, first and foremost via the finest of fine root hairs. These single-cell outgrowths occur all along the length of the growing tips of the fine roots. In some cases they are so minute as to be impossible to see without the use of a magnifying glass, while in others they are large and long enough to be noticeable. The process of osmosis is a simple one and is worth investigation at this point.

A sturdy set of aerial roots on a Banyan Fig (Ficus retusa), which makes for a particularly effective bonsai in the Root-over-Rock Style.