Part 23 of a series by Eugene Howell
Bonsai hobbyists spend a majority of their “bonsai time” looking at and working with, the trunk, branches and leaves of their trees, but keep in mind that one third of the bonsai tree isn’t visible and yet needs a good deal of thought and care placed on it. This, of course, is the root system. Healthy bonsai roots are critical to the general health and vigor of the tree, but since they are out of sight, they’re often out of mind. Most of us only think about the roots when it’s time to re-pot, and then the thought process only encompasses whether or not the roots need to be trimmed.
The health of a bonsai’s root system is just as important to the tree as all its other parts. As a matter of fact, some would argue that there is no other part of the tree that’s more important than the roots because it is there that all of the nutrients and water are absorbed into the tree. The roots are also where the tree stores the great majority of its emergency ration of food and where the tree gets its ability to remain standing upright. A plant can get along without its leaves for several weeks and can easily survive when all its branches are removed (which is a typical way to initially begin styling a Ficus) yet if we remove too many roots the tree will die within just a few days.
So let’s spend some time discussing bonsai roots and how to keep them healthy.
The root system of a mature tree in nature is actually larger than the canopy of the tree. It normally extends two or three times further from the trunk than do the branches. There are two reasons for this. First the root system needs to be far spreading in order to find enough water and minerals and secondly, it provides what’s above ground with enough stability to withstand strong winds and its own far reaching, heavy branches.
The tree needs a constant supply of food and water to survive. These enter the tree through the root system. Dissolved minerals and water are absorbed, by osmosis, through the root hairs along the tips of each small root. These nutrients are carried up to the leaves where they are converted into complex carbohydrates, which are the food that the tree uses.
Each of the root hairs is actually only one meristem cell which has elongated to protrude a few millimeters from the surface of the root. By osmosis, the dissolved minerals are passed into the root hair and then, by fluid pressure, passed through the xylem layer all the way up to the leaves.
One question that arises is “What causes the water and dissolved minerals to move into the root hairs?” The answer is one of simple chemistry. If there is an area with higher concentrations of salts next to one with a low concentration, water and its dissolved minerals will move toward the area of higher concentrated salt in an effort to dilute it. In the case of root hairs, the liquid inside each hair is of a higher salt content than the water in the surrounding soil so the water in the soil moves into the root hair. This is the reason you never want to apply too much fertilizer to a plant. Doing so can reverse the salt concentrations making the content in the soil higher than that in the roots and thus causing water to leave the roots.
(To be continued in part 24)
Photo credit: flickr Creative Commons, Bonsai Roots Detail by Tony Atler