An Introduction to Bonsai Soil

When someone mentions the word “soil”, most folks think “dirt” – like the stuff you find in your garden.  Consisting of what you add to it in terms of loam and fertilizers and what falls and rots back into it, that dirt is not the same as bonsai soil.

Why? Bonsai soil is an easy term for a matrix that is the support structure that contains the material that contains the water that contains the nutrients for your bonsai tree.

Is that still a bit muddy?

What Bonsai Soil Really Does

Think of it this way – your bonsai is a miniature tree.  It’s in a small container.  The roots are the structure through which it takes nutrients into the tree.  Roots require oxygen to grow.  Oxygen moves through air faster than it does through water.  The water that drains out is replaced by air. 

If the “soil” that you use for your bonsai potting medium doesn’t allow for the proper absorption of nutrients, water and air, your bonsai will not thrive and, perhaps, die.

Therefore, bonsai “soil” needs to be a medium made of particles with the ability to hold moisture, with good drainage, that supports root growth.


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Most “dirt” is too fine, compacting over time; and, doesn’t allow for good drainage, becoming sodden, causing root rot and can lead to other fungal infestations.

What It Needs To Be 

What does Bonsai soil need to be, then?  There is no “best” soil for your bonsai.  You need to take into consideration what’s your bonsai species and what’s your climate.  In addition, remember that, compared to a full-growth tree, your bonsai is in a container.  Containers hold more water than Mother Earth.  Shallow containers hold more water (thus, less air) than deep containers.  Therefore, decreasing the depth of your pot increases the need for porosity, allowing draining water to be replaced by air. 

There are many (and conflicting) “recipes” for bonsai soil.  However, there are two questions to remember:

  • Will it retain water properly and absorb nutrients from the air?
  • Will it drain water properly? 

There’s also discussion about whether your bonsai soil should be a blend of organic and/or inorganic material.  Examples of organic material are:  dead plant matter, such as peat, leaf-litter and various barks.  Examples of inorganic material are:  volcanic lava and baked or fried clays.  Generally, organic material continues to break down and can become compacted.  While inorganic material sustains their open structure, without breaking down as quickly. 

Three Essentials 

No matter what material you choose for your bonsai potting medium, remember that all bonsai soil needs three essentials:

  • Drainage – water must be able to drain immediately.  Lack of good drainage means too water-retaining, causing lack of aeration 
  • Aeration – particles in bonsai mix are sufficient size to create air spaces between each particle as oxygen encourages healthy roots
  • Water Retention – holds enough water to supply moisture between watering

Your bonsai is confined to a small portion of soil on which its life depends.  Through that medium your tree must obtain water, nutrition and air to grow.  The quality of your soil will affect the vitality of your bonsai tree.


DISCLAIMER: The content provided in this article is not warranted or guaranteed by Bonsai Outlet. The content provided is intended for entertainment and/or educational purposes in order to introduce to the reader key ideas, concepts, and/or product reviews. We are not liable for any negative consequences that may result from implementing any information covered in our articles or tutorials. Happy bonsai gardening.