Caring For Bonsai Trees – What’s There To Know About Root Pruning?

bonsai trees

It is widely known that the secret of keeping your bonsai both healthy and miniature is to prune not only its branches but the trunk and roots as well. Pruning is a bit scary to newcomers to the hobby of caring for bonsai trees, as pruning roots damages a plant, restricting its ability to take up water and nutrients while pruning branches must be done carefully to ensure that you end up with your desired shape.

The time when your bonsai will need its roots trimmed is usually between one and five years after you bought it. This time frame is only a guide for caring for bonsai, as a number of factors effect the amount of time a tree takes to become rootbound in its pot; different species of tree have different levels of development and the variables such as the size of the pot, the development of the rootball and the age of the tree all have an influence on the growth of the roots.

When you take the tree out of the pot to inspect it each year, usually in the spring, you will be able to see if the roots need pruning. If you find that the roots form a circular ball around the edge of the pot, it’s time to trim or prune the roots. If the roots of the tree are still contained within the soil, the tree can be returned to the pot and pruning can be left for another year.

There is a tool specially designed to help you expose the roots. This is called a “root hook” but it doesn’t have to be this specific tool. You could try either chopsticks, screwdrivers, or a crochet needle as what you are trying to do is to gently work in between the roots to loosen the soil surrounding them.

While you have got the roots exposed, this is an good time to inspect the roots for early signs of decay and rot. It is vital when caring for bonsai trees, that we remove these dead roots as they will cause trouble in the future if we do not get rid of them.

You need to know how much root to cut off and how to select the right roots to be ‘cut back’ to a degree to keep them healthy and small enough for the pot.

Look for the long large roots that dominate the pot and trim them back. In particular, look at the downward growing roots. These need to be removed as they will eventually begin to ‘lift’ the tree out of the pot.

What we are trying to achieve here is to make way for the smaller feeder roots that will continue to sustain the growth of the tree while keeping the root system small enough to survive in the small pot.

You want the root system to spread laterally, from the trunk base or nebari rather than downwards, like anchors.

It is best to use a sharp knife or shears when cutting the roots and try to cut them with a downward slant. When you do this, there is less chance of water gathering in the exposed part of the newly cut root which in turn lessens the chance of infection setting in.

It is important when caring for bonsai trees that you do not remove more than 30% of the roots in any one year. This is important as you don’t want to reduce the root mass to the stage where it can’t support the tree so, generally aim to only remove about 1/3 of it.

Although there is a lot of information available on caring for bonsai trees, the pruning element still seemed to be rather daunting to me. It was difficult to have the confidence to do actually cut the roots for the first time.

I found that the best thing to do was to find a person experienced in caring for bonsai trees and watch them before I attempted to do it myself. Once I had seen it done, I had the knowledge on what to trim and what to leave and I could get on with the task of pruning my bonsai, confident that I was doing the right thing for my tree.

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