Introduction

Root rot is one of the most common diseases that can affect bonsai trees. This is because growing a tree, and keeping the roots healthy, in a restricted environment like in a pot, on a slab, or on a rock, requires different horticultural techniques than those used for managing trees grown in the ground or a nursery pot environment.

The functional roles of tree roots are somewhat comparable to those of the branches and leaves for keeping a tree healthy. We know that our trees have roots, but since they are hidden under the ground, it's hard to imagine that they look much like the above ground branches. In fact, the roles of roots are just as important as those of the foliage. This is why we should try to take as much care of these underground parts as we do for the above parts of our trees.

What is a healthy tree ?

Figure 1. Main functions of a healthy tree

A healthy tree is a tree that is exempt of stress, pests and diseases and growing in an environment where it can get everything it needs for its normal growth.
Figure 1 shows the two mains functions of a healthy tree which could be compared to those of a chemical factory, functioning in harmony with its foliage and roots. Above ground, the leaves are manufacturing food and energy that need to be sent downwards to the roots for growth and, below ground, the roots are absorbing water and minerals that are needed for the leaves to function properly.

Both roots and foliage have to be healthy for the efficient transport of food and minerals throughout the tree. In a healthy tree the root system can also perform other vital functions such as accumulating winter reserves of essential foods needed by the tree to produce spring foliage, as a habitat for its important symbiotic relationship with mycorrhizal fungi and by creating a rhizosphere for nutrient uptake and the activity of many beneficial soil microorganisms.