Soil Matters: Exploring the Foundation of Bonsai Health

Soil Matters: Exploring the Foundation of Bonsai Health

By: Maarten van der Hoeven Comments: 0

How to use the different types of bonsai substrates

The right bonsai soil and mix are of great importance for the health and growth of a bonsai. Drainage and water absorption are important, but that's not all:

  • Drainage and Water Absorption: A good bonsai substrate should provide adequate drainage to prevent water from remaining in the soil for too long, which can lead to root rot and other health problems.
  • Nutrition: Bonsai trees have specific nutritional needs and the right substrate can help meet these needs. For example, some bonsai substrates, such as akadama, can add nutrients to the soil.
  • Aeration: A good bonsai substrate should also provide enough aeration to help the roots breathe and prevent them from suffocating.
  • Stability: A bonsai needs to be sturdy in the pot, and the right bonsai substrate can provide this by providing adequate support.
  • Durability: Some bonsai substrates, such as soil, can quickly acidify or become depleted. A good bonsai substrate will last longer and promote consistent growth.
  • By using the right bonsai substrates, you can ensure that your bonsai stays healthy.

With this blog we hope to help you understand the characteristics of the different types of soil and soil mixtures, and on how you can use different types of bonsai soil. It is important to note that the type of soil you use will depend on the species of your bonsai tree and its specific growing conditions, your garden, your water and other factors. It is best to consult an experienced bonsai grower before choosing a specific type of soil or soil mixture.

There are several types of bonsai soil that are very suitable for growing bonsai trees. Below we describe the characteristics and typical use of the most commonly used:

  • Akadama - a specific species of Japanese soil that provides the perfect balance between water and air.
  • Kiryu - a slightly acidic soil that provides a better drained soil mixture.
  • Kanuma - an acidic soil specifically recommended for acid-loving plants such as azaleas and camellias.
  • Pumice stone or bims - a volcanic stone with a porous and light structure that helps to remove excess water and introduce air into the soil.
  • Lava Rock - a volcanic rock that is airy and permeable to water and helps to remove excess water.
  • Bamboo charcoal - Bamboo biochar provides a habitat for beneficial microorganisms in the soil and is slightly alkaline in nature, which can help regulate the pH level of the soil.
  • Keto - black peat clay, also known as kaolin clay, can be added to bonsai soil mixes to improve water retention.


Akadama is a type of volcanic soil widely used in bonsai cultivation. It comes in two forms: hard akadama and baked akadama. It is a volcanic clay soil that is well drained and has a high mineral content.

Bonsai Plaza has double line hard quality (baked) akadama in 6 types of packaging:

  • Shohin akadama 14 ltr. fine grain size: 1 - 3 mm 
  • Akadama 2 ltr. normal size grain size: 1 - 5 mm 
  • Akadama 5 ltr. normal grain size: 1 - 5 mm 
  • Akadama 14 ltr. normal grain size: 1 - 5 mm 
  • Akadama 14 ltr. large grain size: 5 - 10 mm 
  • Baked akadama 10 ltr. normal grain size: 3 - 5 mm

All akadama soil breaks over time and needs to be replaced periodically. Our hard quality akadama needs to be replaced less often than other qualities.
Baked akadama is more expensive but technically preferable for bonsai to regular hard akadama because it is sterilized and more durable and retains moisture better. Baking the akadama, usually at 800 degrees Celsius, removes all organic matter, reduces the risk of mold growth, and sterilizes the soil to eliminate any pests or diseases that may be present. Baking also makes the soil more durable and helps retain moisture longer, which is essential for bonsai tree health. Plain hard akadama can break down faster than baked akadama, leading to faster soil compaction and poor drainage.
To use akadama in bonsai, you can mix it with other soil components. Akadama is often mixed at a ratio of about 70% akadama to 30% other components, such as pumice or lava rock to create a more permeable mix, but can also be used neat. The ratio of akadama to other components depends on the specific type of tree you are growing and the specific conditions in your yard.
When repotting your bonsai, make sure to carefully remove the old soil and trim the roots before repotting the new akadama mixture. Be sure to water the tree well after repotting.


Kiryu soil is a type of soil that is widely used in bonsai cultivation, especially for conifers such as pines and junipers. It is a soil extracted from the Kiryu region of Japan, it is a volcanic soil mainly composed of volcanic ash, pumice and peat moss. Like Kanuma soil, it has a very low pH of around 4-5 and is similar in properties and characteristics, such as good drainage and the ability to retain moisture, which is important for bonsai. It also has a high cation exchange capacity, meaning it can hold nutrients and make them available for the plant to absorb.
It is important to note that Kiryu soil is not a substitute for all types of bonsai, as it will change the acidity of the soil if mixed with another type of soil. It is important to match the soil to the plant species and not to overuse it, as it can lead to nutrient deficiencies if not mixed with other soil components.
Bonsai Plaza has Kiryu in 3 types of packaging:

  • Kiryu 3 ltr. normal grain size: 1 - 5 mm 
  • Kiryu 14 ltr. normal grain size: 1 - 5 mm 
  • Kiryu 14 ltr. large grain size: 5 - 10 mm 


Kanuma is a lightweight, rocky volcanic rock which is found in Japan. It has a sandy and airy texture and very low nutrient content. It is a popular soil component for acid-loving species such as azaleas and camellias because of its texture and acidity. Kanuma has a very low pH (around 4-5) and mixing it with another higher pH ingredient such as akadama will change the acidity of the mixture as a whole. For most species, it is recommended to mix kanuma with other soil components such as akadama or other soil with a neutral pH such as pumice, lava rock or expanded clay, at a ratio of approximately 30-50% kanuma to 50-70% other components to form a soil mix to create suitable for bonsai. A thin layer of kanuma can be used as a ground cover to protect the soil from drying out.

Bonsai Plaza has kanuma in 2 types of packaging:

  • Kanuma 5 ltr. normal grain size: 1 - 5 mm
  • Kanuma 16 ltr. normal grain size: 1 - 5 mm

Pumice stone or bims

Pumice or bims is a type of volcanic rock often used in bonsai soil mixes. It is valued for its porous and light structure, which ensures good water drainage and air circulation around the roots of your bonsai. Pumice is also pH neutral and will not decay over time, making it an ideal ingredient for bonsai soil. When used in a bonsai soil mix, pumice helps to prevent soil compaction and provides ample support for the roots, allowing the tree to thrive. It is often combined with other materials, such as akadama, lava rock and bark, to create a well-draining, nutrient-rich growing medium for bonsai trees.

Bonsai Plaza has pumice in 8 types of packaging:

  • Japanese pumice stone (white) 15 ltr. normal grain size: 3 - 5 mm
  • Japanese pumice stone (white) 15 ltr. large grain size: 6 - 10 mm
  • Ezo pumice stone (yellow) 16 ltr. normal grain size: 3 - 5 mm 
  • Hyuga pumice stone (grey) 15 ltr. normal grain size: 3 - 5 mm
  • Matsu pumice stone 5 ltr. fine grain size: 2 - 3 mm
  • Matsu pumice stone 5 ltr. normal grain size: 3 - 5 mm
  • Matsu pumice stone 14 ltr. normal grain size: 3 - 5 mm
  • Matsu pumice stone 14 ltr. large grain size: 6 - 10 mm

Lava rock

Lava is a porous material that retains water and air well, but it lacks other important nutrients needed for bonsai growth. For this reason, it should be mixed with other substrates to ensure that the bonsai gets all the nutrients it needs.

Lava can also be used as drainage in the bonsai's pot. Place a layer of lava at the bottom of the pot before adding the soil mixture. This will drain excess water and prevent the bonsai roots from rotting. Be careful with trees that are sensitive to drought: Although lava holds water well, it can also dry out quickly. If you have a bonsai that is sensitive to drought, you should water it more often with lava and make sure that the soil mixture is always moist.

Keep in mind that different types of bonsai have different needs when it comes to soil mix. Feel free to ask us for tailor-made advice.

Bonsai Plaza has lava in 2 types:

  • Fuji lava black 10 kg. normal grain size: 3 - 5 mm
  • Matsu lava black 14 ltr. normal grain size: 3 - 5 mm


Keto black peat clay, also known as kaolin clay, can be added to bonsai soil mixes to improve water retention. This means it can help keep the soil more moist without creating standing water. When adding keto to the bonsai soil, it is important to mix it in small amounts so as not to disturb the water retention of the soil.

In short, Keto:

  • is used for rock and forest plantings.
  • holds a lot of moisture.
  • is very malleable, making it easy to shape.
  • is slightly tacky so it doesn't fall off the rock.
  • is excellent breeding ground.

In bonsai it is advisable to mix keto with different soil types, such as akadama, pumice and keto, to find the optimal balance for your specific bonsai species.

Bonsai Plaza has Keto in 2 packaging units: 1.2 liter and 15 liter.

Bamboo charcoal

Bamboo charcoal, also known as bamboo biochar or bamboo carbon, is often used in bonsai soil mixtures for several beneficial reasons:

  • Improved Drainage: Bamboo charcoal has excellent porosity, allowing for better air circulation and water drainage in the soil. This helps prevent waterlogging and root rot, ensuring healthier bonsai roots.
  • Moisture Regulation: Bamboo charcoal has the ability to absorb excess moisture and release it slowly when needed. It helps maintain optimal soil moisture levels, reducing the risk of overwatering or underwatering the bonsai.
  • pH Regulation: Bamboo charcoal is slightly alkaline in nature, which can help regulate the pH level of the soil. It buffers acidity and creates a more balanced environment for the roots, promoting their health and nutrient uptake.
  • Odor and Toxin Absorption: Bamboo charcoal has natural deodorizing properties and can absorb harmful chemicals or toxins in the soil. It helps purify the soil environment, creating a healthier and more conducive growing medium for the bonsai.
  • Microbial Activity: Bamboo charcoal provides a habitat for beneficial microorganisms in the soil, promoting a healthy soil ecosystem. These microorganisms aid in nutrient cycling and contribute to overall soil fertility.

Overall, using bamboo charcoal in bonsai soil mixtures can improve soil structure, drainage, moisture regulation, pH balance, and the overall health of the bonsai tree. It is a valuable addition that can support the long-term well-being of the bonsai.

Happy bonsai gardening

In conclusion, selecting the right soil for your bonsai is crucial for its long-term health and vitality. By considering factors such as drainage, aeration, and nutrient retention, you can create the ideal growing medium for your miniature tree.

Remember to regularly monitor the soil's moisture levels, repot when necessary, and adjust the composition as your bonsai matures. With proper soil care, your bonsai will thrive and bring you joy for years to come.

We hope you now have a deeper understanding of the importance of soil in the cultivation of these magnificent trees. By dedicating time and effort to understanding and improving your bonsai and bonsai soil, you'll be rewarded with beautiful, healthy trees that captivate and inspire. Thank you for joining us on this bonsai soil adventure, and happy bonsai gardening!


Warmest regards,


Maarten and Jacqueline




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