How To Get Rid of Mold on a Bonsai Tree

Growing a bonsai tree isn’t always easy, but it is a lot of fun and somewhat challenging at the same time. Most gardeners enter into the hobby understanding that it will be a lot of work. No matter how diligent you are there will be times when a bonsai tree will experience an infection, mold or disease. There are many types of molds and mildews that can affect your bonsai. Identifying and knowing how to get rid of mold on a bonsai tree is prevalent to ensure your plant remains healthy and thriving.

Here is a look at a number of different molds that can give you trouble as well as steps to take to get rid of mold on a bonsai tree.

Two Common Classifications of Mold Found on Bonsai Trees

There are a number of fungal diseases that can affect your bonsai tree. These diseases may affect the foliage, the roots or the branches. In most cases, they are caused by the plant being exposed to prolonged wet or humid conditions. When the soil is too wet for too long it can contribute to the growth of mold and fungi. Even though bonsai trees have a strong defense mechanism, if wet conditions continue, it can overwhelm the tree.

The two basic classifications of mold typically found on a bonsai are pathogenic and nonpathogenic. Pathogenic molds are found residing in a poor soil mixture. They are not a type of mold that provides any benefit for the soil composition. Phytophthora and Pythium are examples of common molds that look to healthy roots to help provide nourishment and replication. As the mold continues to grow, it will intercept the nutrients from moving up from the roots to the main stem. A pathogenic mold may not be noticeable until it has started to significantly affect the growth above the soil and the damage becomes visible above the soil.

A minor fungal infection is not usually very serious and can be treated easily enough. However, extensive mold or prolonged fungal attacks can end up severely damaging the bonsai tree and require more drastic measures.

Fungus on the leaves can appear as orange, red, or brown spots. If you look at them using a magnifying glass, you’ll see these spots have a central area that is surrounded by rings. You should also notice very fine hairy-like filaments sticking up from the leaves. If left untreated, older fungus spots start to change colors to brown or black. These types of fungal spots can be on just a few leaves or they may appear on several. New leaves that form also become susceptible to fungal growth. Some tree species are more likely to develop fungus or mold on the leaves, branches, or roots.

Beneficial fungi in the soil are there specifically to help decompose organic matter, broken branches and dead leaves for example. However, when even a healthy bonsai plant is overwatered, it can create an atmosphere in the soil that causes suffocation as the oxygenated spaces are overtaken by water molecules. The roots start to die from lack of oxygen and the nonpathogenic mold starts to break down the roots. When this type of fungi affects the plant, the tips of the roots will appear black and be soft when touched. A lot of times, this condition isn’t discovered by gardeners until the bonsai plant is being repotted. By then, the blackened ball of roots is hard to miss.

Does My Bonsai Tree Have Mold Or Another Disease?

Numerous types of diseases, molds, fungi, and viruses that can affect a bonsai plant. The tree might show some signs to let you know it is in trouble.

Usually, a bonsai tree with mold or disease will exhibit at least one of these symptoms:

  • Flowers and leaves that are distorted or discolored
  • Losing leaves when it’s not the right season
  • Leaves that start to yellow, wilt, dry, or fall
  • Slowed growth
  • Branches that start drooping or wilting
  • Shoots and leaves that start showing signs of dying starting at the very tips

How Do I Treat Mold Or Disease on My Bonsai Tree?

If you find evidence of a disease or mold, your first priority becomes preventing it from spreading to other areas of the plant. It’s also important to keep it from affecting other plants that might be close to the bonsai tree that is affected by mold or disease.

Your bonsai needs to be examined regularly for any signs of mold or infection. If you examine the plant regularly, problems can be identified earlier. This lets you take the steps needed for your bonsai tree to recover. If the mold or disease is unaddressed, it can cause severe damage to the tree and can, ultimately, be fatal. If your plant becomes infected with mold or disease, follow these steps.

  1. Remove the tree from the area if it is close to other pants. This prevents cross-contamination or the spread of mold, infection, or disease.
  2. Remove the area of the plant that is affected. This is usually leaves, but not always.
  3. Spray the recommended fungicide on the plant’s healthy foliage.
  4. Check for any possible causes of the problem. This might include root rot, over-watered soil, or poor ventilation.
  5. Sterilize any tools you use to prune the tree.
  6. Place the treated bonsai tree in an area with proper ventilation and good lighting to prevent reinfection.

When dead leaves and debris builds up around bonsai plants, it creates a moist and humid environment that encourages mold growth. Having the soil too moist can lead to root rot and the growth of various fungi and mold. If the area is too humid, moisture can also cause fungus to grow on the leaves and branches. Treating fungus and mold on the leaves and branches is somewhat easier. Some tips include:

  • Increase the air movement around the tree using a fan.
  • Don’t mist the foliage or branches.
  • Try to keep them dry so moisture doesn’t build up.
  • Treating it with an anti-fungal can help get rid of fungus and mold, especially if it’s stubborn.

Bonsai Root Mold Removal

When roots are attacked by fungus or mold, it’s usually because they were too wet for too long. The most effective way to battle bonsai root mold is to remove it completely. You may notice the roots change colors going from a healthy brown to black. They may also have an odd odor. To treat affected roots, the tree will need to be replanted. All the fungi, both pathogenic and nonpathogenic need to be cut from the main bonsai plant roots.

Most gardeners keep bonsai in a planter so it’s easier to remove all the soil and discard it. The planter should be cleaned completely using a disinfectant that fights fungal mold. Pruning the plant and putting it in new soil give the bonsai the best chance of re-growing back into healthy shape. Make sure to replant the bonsai into a more open pot that drains well. Double-check the best watering schedule for your type of bonsai tree and begin a proper watering regimen. You may also treat the bonsai with an anti-fungal soil drench.

how to get rid of mold on bonsai

Identifying Specific Molds and Fungi Commonly Found on Bonsai Trees

These are the various types of molds and fungi that can attack bonsai trees. Here are some of the most common molds you are likely to find and how to identify and treat them.

Black Spot Fungus

This type of fungus attacks the foliage of the plant. You can identify it by black patches or spots on the leaves. If it is not treated with an appropriate anti-fungal, the leaves will turn yellow, shrivel up and start to fall off. Remove any infected leaves from the tree to help prevent it from spreading.  A fungicide can be sprayed on the healthy foliage. Don’t water the tree until you’ve removed all the affected areas.

Leaf Spot Fungus

The Leaf Spot fungus is similar to Black Spot as it is characterized by black, brown, gray, or white spots depending on the species. These spots may appear on leaves, twigs, or branches. When they first appear, they are usually white and then change to darker colors as the disease progresses. Lesions will develop eventually, and the foliage will begin to wither and finally die. As soon as you see Leaf Spot fungus, remove any affected fruit, leaves or branches. Clean the soil so it’s free from debris and then spray the remaining healthy foliage with a fungicide.


Mildew, or mold, is a type of fungus that thrives in a damp environment, especially when there is not enough sunlight and little ventilation. You may notice powdery mildew or a sooty mold begins to form on foliage, branches, or stems. It can cause discoloration, distorted growth, and dieback. It’s not possible to totally eliminate mildew from the leaves. Once it’s detected, all affected shoots and leaves have to be removed immediately. Spray the bonsai with a fungicide to prevent it from occurring again. Sometimes, Black Sooty Mold is caused by too many aphids or scale insects. You will need to remove these little pests using a mild insecticide. Make sure to move your bonsai to an area with plenty of ventilation and adequate sunlight.


Rust is a fungal disease that will show up as yellow, red, brown, or orange blisters or raised bumps on the bottom side of the plant’s leaves. If it’s not treated, the leaves will start to curl and then fall off. A rust infection is not always fatal for a bonsai, but it can cause serious damage. Remove any affected parts of the plant, then treat the healthy foliage with a fungicide. Make sure to move the bonsai to a well-ventilated area that has adequate sunlight.

Remember that prevention is the best way to protect your bonsai from disease and mold. But don’t feel bad if your plants fall victim. Even the healthiest plants can be affected sometimes. Just learn to recognize the signs of mold or disease and provide quick treatment when it is discovered. This helps the plant have the best possible recovery chances and helps protect your other trees from being affected if you have a collection.

Preventing Mold and Other Diseases on Your Bonsai Tree

Improper care is often the culprit, but certainly not always. Mold can cause the tree to become stressed or sick and then it is more susceptible to other diseases and illnesses. A bonsai tree that is strong and healthy to start with, is less likely to contract mold or fungi. It’s also less likely to get other plant viruses and diseases. Prevention really is the best medicine.

Prevent fungus, molds, and diseases by:

  • Keeping the bonsai tree and soil clean and free of debris and dust.
  • Keeping the soil free from leaves, fruit, or blooms that have fallen off the tree or nearby plants.
  • Providing enough ventilation, fresh air, and lighting.
  • Making sure the soil is aerated adequately, isn’t packed too tightly, and replenished when it needs it.
  • Repotting the bonsai so the plant doesn’t become pot bound.
  • Applying fertilizer as needed.
  • Pruning appropriately and applying a wound paste afterward to encourage healing.

Final Thoughts

Most of the time, if a bonsai tree is well-cared for it will remain healthy and mold-free. However, even the best gardener will experience mold or other diseases on a bonsai at some time or another. Knowing how to get rid of mold on a bonsai is a necessary skill for all gardeners. Not only will these tips help you prevent it from occurring, but they will help you identify it quickly so treatment is fast and effective.

how to get rid of mold on bonsai Cover

Recent Content