Part 24 of a series by Eugene Howell
In the previous post we learned the importance of the health of a bonsai’s root system and how the root hairs function. We also learned why water will move into a root hair and what can cause that process to reverse, causing harm or death to the bonsai. In this article we’ll continue discussing how to keep your bonsai tree roots healthy.
With the exception of desert plants, bonsai trees like to have their roots in moist, but not wet, soil at all times. This means that the soil must never be allowed to completely dry out or the tree will quickly die. If you discover one day that your bonsai is wilted and has drooping leaves but was in perfect health the previous day, it’s safe to assume you probably forgot to water it. Watering to often, however, can also harm the tree because it can allow root rot to set in.
The composition of bonsai soil will affect the health of the tree’s root system. The more dense a soil (too much clay and decomposed organic material), the slower it drains and the higher the probability of retaining too much moisture. Also the more dense the soil, the weaker the root system will be. Here in Florida we generally use an almost inorganic, very coarse planting medium. This provides a fast draining environment that retains just enough moisture for the following 24 hours. A coarse soil provides a multitude of tiny spaces for air and this aids the growth of the roots.
A root bound tree:
If your bonsai is otherwise healthy and growing vigorously but suddenly has the leaves beginning to turn brown or drop off, and you know you’ve been watering it regularly, it may be a case of being root bound.
Every bonsai hobbyist knows that bonsai need to be repotted every few years. If not cared for, bonsai tree roots can grow and grow to the point that they become more like a block of wood in a pot instead of a healthy root system. When a bonsai’s roots grow to where they completely fill the pot they have become root bound. When this happens the mass of wood inside the pot prevents water from draining through the pot and causes it to merely over flow the edges of the pot, like rain pouring onto an umbrella.
Because repotting is done on a bonsai only once every few years, it should be taken as an opportunity to carefully examine the tree’s root system. While the bonsai tree roots are exposed and spread out, look for roots that are spongy or of an unhealthy color. An unhealthy color is one that is dark brown or black when the root is scraped with your fingernail. If you find any, remove them so that only strong healthy roots remain.
While the roots are exposed, keep in mind that they must remain moist at all times. This means that you’ll need to spray them with water frequently to prevent them from drying.
By caring for your bonsai tree’s roots in addition to its leaves and branches, you’ll always have a magnificent healthy bonsai.
Photo credit: flickr Creative Commons, Roots by Stephen Bowler