Why do bonsai roots rot

Why do bonsai roots rot? [ Best guide ]

Many of my bonsai trees died due to this root rot. So I did a lot of research to find the reason for root rot. I found,

Why do bonsai roots rot? Inappropriate moisture in the soil due to lack of drainage is the main reason. Otherwise, Less aeration, Root rotting fungi, Over-fertilization, Unbalanced water, exposure to freezing temperatures, and damages due to root pruning are Causes of root rot problem on bonsai.

But it is possible to protect your bonsai tree from root rot by following some special guidelines. All of them are here.

Why do bonsai roots begin to rot?

There are many causes for the problem of root rot in bonsai trees. Many bonsai trees die due to this root rot, and mainly it happens because of less attention. Why don’t you pay attention to your loving bonsai tree?

Any kind of bonsai tree from any species can be affected by this root rot disease. Mainly root rot is consequences of climatic changes and Excess moisture. And there are so many other reasons.

But all of those reasons are under your control. The only thing you want to do is pay good attention to your bonsai trees. Many bonsai gardeners grow various species of bonsai trees, and some of those trees have the drought-tolerant ability, and some of them have moisture tolerant ability.

But only the least number of species are able to tolerate high moisture and drought. So if you didn’t understand the ability of your tree, it would die. So, first of all, identify your tree.

If you want to identify the ability of your tree, read about drought-tolerant and moisture-tolerant Bonsai trees. Now let’s check the reasons that course this root rot on Bonsai trees are.

Inappropriate moisture in the soil.

Mainly root rot happens due to inappropriate moisture in the soil. As you read earlier, there are various types of trees with multiple abilities. Most of the trees that used to grow as bonsai do not have moisture tolerant ability.

Such trees have Weak root systems, and they start to rot when they feel more moisture in the soil. Mainly high moisture in soil happens due to less drainage facility of bonsai pots.

So you should to be extremely careful when selecting a bonsai pot for your tree because you have to choose the appropriate bonsai pot for your bonsai tree unless it will hard to keep alive.

How moisture affects root rot.

For the growth of any plant or tree, moisture is a significant factor, but overwatering is dangerous for plants. Because it increases the moisture of the soil than the wanted amount.,

Moisture affects root rot in various ways. Mainly bacterial growth around roots happens because of inappropriate moisture. On the other hand, Roots want to absorb some air through the soil, but if the moisture in the soil is high, roots can’t absorb air, so it’s also a reason for root rot.

When we consider stagnant water around the root is harmful. It makes a favorable condition for various viruses that affect plant health. On the other hand, bonsai trees cannot manage a vast attack of viruses in a short time. So your bonsai tree will definitely die if you don’t pay attention to the tree.

Also, moisture affects root rot by blocking aeration in the soil. When moisture in soil increases, tiny holes in the soil are closed by water, so its roots can’t achieve air. This causes the boiling of roots, which affects root rot.

What are the reasons for inappropriate moisture in soil?

Inappropriate moisture in the soil means that The wetness of soil is not suitable for a living plant. Mainly this happens cuz over-watering, less sunlight and lack of drainage holes. Also, Exposure to rain is another factor that affects root rot.

Less sunlight

less sunlight causes stagnant water in the plant pot because the water did not vaporize without good sunlight. Mainly due to this, pore spaces under the soil tend to be filled with water. So roots cant reach oxygen through the soil, and due to that, bonsai roots start to decay and spoil.


As we all know, if a plant got too much water in its pot, there is a risk to the life of the plant. Over-watering is a direct thing that causes high moisture. When you supply more water than needed to the pot, it starts to pool around the tree, so Spontaneously moisture rises up.

Lack of drainage facility

Lack of drainage is an important factor that we should observe among all the above reasons that lead to improper moisture in bonsai soil.

When we consider the lack of drainage facilities, first of all, you have to identify what is drainage facility. It is the facility that allows water to go through the soil and come out from the pot.

So when this drainage facility did not work in your bonsai pot, it is a huge problem that causes excess moisture in the soil.

Mainly this happens due to fewer drainage holes in a bonsai pot. If there are not enough drainage holes on the bonsai pot, the soil can’t remove excess amount of water. So pooling water blocks the pore spaces. So when you buying a bonsai pot, you have to check the weather if there are enough drainage holes on the pot. Before you buy a bonsai pot, read this highly recommended article, Do bonsai pots need drainage holes ”

Exposure to heavy rain is also affecting the inappropriate moisture in the soil and can have bad consequences. If a bonsai tree is exposed to heavy rain, roots start to rot at high speed than regular water. Because rainwater contains various acids that did not find suitable for bonsai trees.

Why do bonsai roots rot
spoiled bonsai root

Less aeration in the soil

You must know that every tree prefers to absorb air through its root system. As well as bonsai trees also do like to absorb air from the roots.

In the first place, you should understand that bonsai trees are made up of a weak root system for the first few years until they get mature.

When we grow bonsai trees, as bonsai gardeners, we know that bonsai trees have a tied root system like a nest. Bonsai roots have less space to grow, so pore spaces in the soil are significant when growing roots.

So as in the topic, Aeration is a significant factor for bonsai root health. Mainly aeration is supplied by the pores in the soil.

Aeration depends on the soil moisture, the size of the bonsai pot, and the type of soil you use. So if any above-mentioned factor is missed, your bonsai tree roots will start to rot, and soon your bonsai tree will die.

The size of the bonsai pot can cause root rot.

Since I was originally a bonsai gardener, I had a big problem with bonsai trees often dying due to root rot and root bacteria. I did various observations, and here is one significant factor that I found. It is unsuitable for bonsai pots.

Unsuitable bonsai pots are pots that do not meet the needs of the bonsai plant. If you are a bonsai lover, you should know that the requirements for bonsai trees vary depending on the type of bonsai. So here, we gonna discuss how the size of the bonsai pot affects the root rot of bonsai trees.

The size of the bonsai pot, Aeration, and the root system has a nice relationship. Bonsai trees have a webbed root system because they haven’t enough space to run their roots, and these roots are pruned from time to time.

But bonsai trees do not change their requirements and always try to absorb nutrients from the soil and some amount of air from the soil. That is the place where pore spaces and aeration come to the action. No matter how small the pot is, the bonsai tree tries to absorb what it wants, and if the roots are unable, the tree starts to die.

So aeration is an essential factor when growing a bonsai tree. So you hiate moisture in the soil and can have bad consequences. If a bonsai tree is exposed to heavy rain, roots start to rot at high speed than regular water. Because rainwater contains various acids that did not find suitable for bonsai trees.

Ave to choose the best size of bonsai pot with the required amount of drainage holes. Because drainage holes remove exes amount of water through them and make air tunnels in the soil. So bonsai trees can absorb some amount of air through the soil, or Bonsai roots will die due to high moisture.

And when the size of the bonsai pot increases, the bonsai tree can grow its root in a wide area. It helps the root system to achieve places that there are more pores in the soil. So pick the correct bonsai pot.

The type of soil you use can cause root rot.

You cannot use all types of soil to grow bonsai trees. There are special soil types for specific bonsai trees that suit the needs of the tree.

So when we consider aeration, it mainly depends on the type of soil. The shops have pre-prepared bonsai soil mixes, and not all of them are recommended, and I can recommend a few of them.

But I recommend you make your own bonsai soil mix in your own bonsai yard. So we get to the point. Bonsai soil should not be too muddy. Every bonsai soil must meet the drainage requirement.

Primarily, we mix gravel into each bonsai soil to create a well-ventilated and well-drained soil. If the soil is muddy, it cannot release moisture from the soil, and this causes a pool of water around the tree. As moisture increases, bonsai roots begin to rot, causing your tree to die.

Also read : How to reuse bonsai soil

Root rotting fungi

Many bonsai gardeners have this problem, and I have had this problem too. But I came up with a solution to this root rot because of the fungus. This is not so difficult to remove. The only thing you should do is pay more attention and take care of your plant.

If you are familiar with the types of fungi and their life cycle, you should know that they prefer to grow in places with a good moisturizing environment.

Fungi need to grow by absorbing nutrients from the surface of wet surfaces. So when these fungi and bacteria begin to grow on bonsai roots, the roots begin to decompose.

Various fungi live in the soil and begin to grow when the environment is right, so you need to balance soil moisture to protect your bonsai tree from root rot.

Also, you should keep the plant in a place where it can get direct sunlight and use the best soil without fungus.

Over-fertilization & Unbalanced water

When we consider both Over-fertilization and Unbalanced water, over-fertilization occurs because many bonsai gardeners had lost their loving bonsai trees due to the overuse of fertilizers. Mainly over-fertilization affects root rot in one way.

It is boiling of roots. When I faced this problem, I did many things to stop root rotting. I changed the type of fertilizers many times, but anything did not happen, so I came up with one decision. It is I will stop fertilizing my bonsai trees. After few months, some trees that have started to die Began to become precocious.

At that moment, I understand that this is not a problem with the type of fertilizer. It is a problem with the amount of fertilizer. Now you must understand this.

When we use a large number of fertilizers on our bonsai trees, various types of minerals start to dissolve in the soil, and many of them react with the water and the moisture in the soil and release heat. So when we use more than the required amount, the heat increases, and As a result, the roots begin to boil.

Boiled roots do not have the strength to grow again against bacterias in soil, so bonsai roots start to rot, and it will be the end of your loving tree. So give good attention and use a small number of fertilizers.

Unbalanced water is also a reason for root rot in bonsai trees. As you know, bonsai plants need water in a regular pattern that did not change the moisture in the soil if moisture gets raised. As I mentioned earlier, bonsai roots start to rot.

Other factors that contribute to root rot on bonsai

exposure to freezing temperatures:

Mainly this factor varies with the region where you live. Most probably, bonsai gardeners in regions where they have winter season face this huge problem. So if you have winter season, you must read this.

First of all, winter is not a good time for some bonsai trees. Some bonsai trees are tolerant of the winter, and some trees do not have that ability. Every tree that faces winter has a dormant period, and in this season, the tree did not grow up.

But many trees do not have the ability to survive in the winter season. Here is how freezing temperatures affect the root rot on bonsai. While In the winter period, trees also need water. But if the tree is exposed to freezing cold, the water you put on the tree starts to freeze, surround the roots and thus deactivate the roots.

So when this happens for a long time, roots start to decay and rot because of high moisture. So if you are in a country with a winter season, choose the plants which are tolerant of winter.

Damages due to root pruning

This is not a big factor, as every bonsai gardener has a good experience with root pruning and will look at how root pruning affects root rot.

It takes a long time to grow back when the roots are pruned, and during this time, the roots are not able to deal with the bacteria and fungi in the soil. During this period, the roots do not absorb as much water as before, but water is added to the pot when you water the plant as you did before.

When water is added to the pot, the roots begin to decay and rot. So always remember, when you prune, do not damage the roots and do it very gently, and water your pruned plant carefully.