Are you planning to own or cultivate bonsai plants? Well, it is indeed a rewarding hobby. But if you think that bonsai plants will just sit on their plant and wait for watering and fertilizer supply, you have to think otherwise. They actually require some slightly laborious maintenance procedures. One of them is root pruning.

What is it?

To describe it in the simplest way, it is the process of temporarily removing a bonsai plant from its pot so that its roots can be trimmed. It is the older and thicker roots that are removed and the young ones are left behind. This is because the younger roots are more efficient in absorbing fluids and nutrients from the soil.

This is usually done with a tool called the root hook. It is used to untangle the roots and somewhat straighten then to make it easier to sort out the roots to be removed. In some cases though depending on the bonsai plant, even regular sticks will do the trick.

Why is it necessary?

By nature, plants will attempt to extend the reaches of its roots in order to reach new sources of fluid and nutrient supply. It can expand its reach up to several meters from the plant. This process is not stopped even when a plant is placed in a pot. So in a bonsai, the pot will soon be overly populated by the overgrowth of roots.

This should not be allowed to continue because soon, the soil will be pushed out

of the pot until there is very little of it left and thus causing nutrition issue for the plant. The increased root mass will also increase the bonsai plant’s watering requirement.

When is it necessary?

There are symptoms that you can look out for. Since the increased root mass causes lack of nutrition for the plant, one of the first symptoms that you will observe is general chlorosis. You will also notice a general drop in vigor and appearance of the plant, as if it has lost its vitality.

You may also notice that the leaves are growing smaller and the stems and the internodes are becoming shorter than normal. And of course, the most obvious - if it seems the plant is being pushed up from its pot, root pruning is already being called into practice.

How often is it done?

For most breeds, it root pruning may become necessary at least once a year. Some breeds however may require more than that. Good examples include willow, cherry, apples, plum, malus, and prunus.

However, you may not have to wait for the standard time for pruning to be done. Even if a year has not yet passed, you may need to do it once the bonsai plant begins showing some or more of the symptoms mentioned above.

How does it affect bonsai growth patterns?

Root pruning is not actually just a maintenance procedure. It can also be a very important tool for bonsai hobbyists to control how they want a bonsai plant to grow. By combining how they do top pruning (opposite of root pruning, it removes leaves, stems, etc.) and root pruning, variable results can be expected.

For example, if you want a bonsai with larger leaves and perhaps longer stems and internodes, you will simply have to do top pruning and limit root pruning to only a few trims. The greater root mass will result in more efficient nutrient absorption. But because the top pruning left fewer leaves and stems, what is left will enjoy all the nutrients that are absorbed and thus experience exponential growth.

Now, if you want to limit the growth of the bonsai or make it smaller, all you have to do is remove a lot of roots during root pruning while leaving the top intact. This will result in fewer nutrients absorbed with many leaves and stems to compete for it.

By carefully alternating between these two techniques, a bonsai hobbyist will eventually be able to produce a bonsai with properties that he aimed for.

Root pruning is a very important aspect of bonsai cultivation. As with any plant, if a tree stays in a container for any length of timw, eventually it will become root bound and the health of the plant will be affected. Plants are alwaysin need of moist, nutrient rich material in which to to grow their roots.

This is not an issue in nature, as the roots can travel deep into the ground to find it. The situation in a container is totally different though. Bonsai roots tend to saturate the container with roots. Sometimes, they even will push the plant upward from within the container due to the sheer volume of new roots. When this happens the plant is known as being root bound.

In order to adequately absorb major and minor elements from the soil solution, plants seem to need fresh new root growth. One the first symptoms of a root bound plant is a general chlorosis even thoughthe plant is adequately fertilized. Root pruning bonsai and repotting a root bound plant will invigorate it and cause a flush of new growth.


Some species are slow growing and will therefore require root pruning and repotting less often. Other species grow at a a very fast rate and may require root pruning and repotting two or three times a year. Many flowering species tend to be quite vigorous and will require yearly repotting in order to maintain vigor with quality flower and fruit production. Plants of this nature include Malus and Prunus, apples and plum and cherry.

Usually in small containers most plants will actually colonize the pot with in a single growing season. This is especially true of very small bonsai. Very small bonsai should be repotted every year. Bonsais under ten inches should be repotted every year to two - depending on the species and the growing conditions.

Large potted specimen plants however, may be root pruned and repotted every other year. Sometimes even as long as ten years depending on the actual species. Many large Pines, Cedars and Spruce are quite comfortable with five to ten year root pruning programs.

Plants grown under less than ideal conditions will grow more slowly and therfore require root pruning and repotting equally less often.

The pruning damages a plant, and restricts its ability to take up needed water and nutrients, and so must be done at times of the year that least stresses the plant. For temperate climate bonsais the best times are late autumn and early spring. Tropical plants can usually be root pruned and repotted during periods of slower growth.

In late autumn, deciduous plants have ceased supplying leaves with moisture. Evergreen trees are slipping quietly into winter dormancy. At this time temperatures are cooling and heat stresses no longer an issue. Despite all this slwo down in surface activity, the roots are becoming alive with activity. They have stored an whole season's supply of food and the upper tissues of the plant are still moving food down to the roots. The growth of roots is not dependent on light, but rather only depedent on the supply of food and soil temperatures. Despite air temperatures falling in Autumn, soil temperatures will remain higher since the days are still realitively warm and also because of the radient earth heat. This is especially true for plants that are planted in the ground, or are in contact with the earth.

So long as daytime temperatures are above about 12.5C - 13C (55F) during the day, then the roots are in a hive of activity. By root pruning during this period, you should find that there will be a new flush of root growth before the temperatures fall into the winter range.

Likewise in the spring the temperature stresses are low which means that root pruning will also not cause excessive transpirational losses. In deciduous trees, leaves have not yet formed and so there are no losses there either. In evergreens the foliage is still intact however the temperatures are low enough which means there is no heat stress. Of course spring is a time of rampant plant activity. The dormancy needs have been satisfied and the increasing air and soil temperatures will ensure that both top and root growth will be soon to follow. It is at this time that the roots reverse the Autumn process of storing food and will begin to pump food and water back up to the buds and stems.

Plants can also be root pruned and repotted during periods other than the foliage dormant periods. But be any root loss results in consequential loss of moisture to the upper parts of the plant. Your bonsai will wilt. Pruning during the growing season must therefore be accompanied by a equal amount of top growth pruning to balance the water equation. If you remove too many roots and not enough top growth, then you can kill your plant. A general rule of thumb is to always remove the same percentage of top growth as you do root growth.

Whilst you can root prune and repot at any time of the year under the right conditions by manipulating the environment, beginners should stick always to the safe periods of Autumn and spring.

Bonsai root pruning can also be a very valuable tool in the bonsai training process. Dormant pruning without any top pruning will result in food storage losses and therefore will resultin weaker top growth with small leaves and close internodes. Conversly, dormant top pruning without any root pruning gives the opposite effect. This will reduce the number of buds and also sites for growth and will therefore result in larger leaves, long intenodes and rampant coarse growth.

<< Previous Bonsai Propagation | Back to Bonsai | Next >> Bonsai Shaping