The key to a bonsai trees survival is its roots, and there are some crucial reasons why bonsai tree roots are so important and these are
that the roots:
• transport free water and substances that are dissolved in it into the tree
• store energy reserves and hold water
• make substances essential for the life of the tree
• provide anchorage but less so in bonsai trees as many are wired into their pots
Different tree species though have different roots and the roots will also develop differently in different soil types. Some tree species particularly from more tropical climates will even develop aerial roots or prop roots like the Banyan Fig and some will develop stilts. Great examples of roots growing in weird and wonderful ways can be seen in nature and this can be used to inspire your bonsai tree root design.
There are important differences in the type of roots on a tree, those that are woody roots that provide more structural support and contain lignin and have a corky outer bark and those that are non woody which have very little lignin and no corky outer bark. The non woody roots are the part which can absorb water and the nutrients (micro and macro) that are dissolved in the soil. They do this via their root hairs which are extensions of single epidermal cells. These non woody roots can also be infected by beneficial fungi called mycorrhizae. This is a symbiotic relationship where the mycorrhizae facilitate the absorption of phosphorus and other soil elements. Non woody roots will grow in the winter but only in unfrozen soils but if the pots become frozen the roots will cease to grow. Prior to the winter period to promote root development and health and to encourage strong roots feed with a higher Potassium and Phosphorous fertiliser during the autumn.
Bonsai tree roots are an essential part of the whole bonsai tree design and good roots are developed through well timed pruning and setting out the roots well from the outset. It is key to the survival of your bonsai to sort the roots out first prior to developing the crown and branches which can always be formed later in the bonsai trees development. However this element is often over looked in a bonsai tree, as it is easy to start on the section that is seen and not the below soil section. Another element to the roots though is that of the surface roots or otherwise the nebari which is also a key part of the overall bonsai tree.
Nebari translates from Japanese to mean that of exposed surface roots of a bonsai and a good nebari consists of stable and sturdy roots that extend from the trunk outwards at least from one side to the other gripping the soil firmly. Bonsai trees with a full nebari that is even but does not have to be perfectly regular and well defined are very desirable. The presence of a good nebari promotes a balance of the design of the tree and adds to the impression of the tree’s age and character. Where possible a nebari should be present and roots should spread out evenly from the base of the trunk forming a good buttress; they should be free of exposed hair roots. The roots should radiate from the flare of the trunk and there should be no eye poking roots directly at the viewer. Roots then should be visible on the surface of the soil and look natural. Any wiring used to anchor the tree into the pot through the roots should not be visible which includes wire marks. The most desirable roots are those that are known as “happone” that are all the same thickness and stretch out evenly to create a uniform root formation. Undesirable roots are referred to as “imine” and these include crossing roots as well as roots that are too high out of the soil or unevenly tapered or entwined. Root over rock styles should have their roots firmly attached to the rock and be evenly placed as shown in the image above.
While at the Bonsai World 2011 event, I spent some time observing the roots and nebari of the trees on display and here are some that were worthy of notice in my opionion. The presence of moss also aided to enhance the roots on display in comparison with those trees that were devoid of moss due to the contrast that the moss provided. Furthermore, the presence of the moss added to the naturalness of the setting of the tree and the nebari within the pot.