Akadama. A universal substrate for bonsai

Today we talk about the akadama. Although it may seem like a type of Sushi or a rich Japanese dish with this oriental gastronomic fashion that invades us, we are facing one of the most famous substrates for the ancient Japanese art of vegetable miniaturization called bonsai. A substrate that, when mixed with others, makes the nutritious delights of many of the plant species that have to root in trays of ridiculous depths and obtain everything they need in very little space. Hence it is so special and we will see why.


Substrates for plants are a world. Only with the first three textural components of the soil: sand, clay and silt, we can have an infinite number of substrates based solely on the granulometry (size) of the soil particles. We have already talked about this extensively in other articles such as the one on soil texture . If we also add the contents of macro and micronutrients, aqueous phase, gas phase, available organic matter and other elements, we are facing a mixture of compounds in an almost magical balance that makes a plant, a crop, a garden tree or a bonsai can have their support, their food and their means of root expansion to be there, photosynthesizing and “sucking” all the CO2 they can to metabolize their nutrients.


If you want to know more about substrates, we leave you entries about it.


This is a very easy question to answer and not so easy to apply to reality. The depth of substrate for a bonsai is “zero.” The art is in keeping it on rather flat trays . There they have their entire root system and obviously they cannot extend their roots in search of water or nutrients. So a substrate for a bonsai must be “fluffy” and nourishing and this is summarized in:

  • Very good water retention capacity
  • Very porous, very aerated to avoid root suffocation.
  • A perfect balance between the two previous ones to avoid waterlogging on one side or excessive drainage on the other.
  •  Methodical and highly controlled subscribers .

It is worth us with normal land. No. The art of bonsai is not to emulate nature precisely. It is making sculptures with the trees and that requires certain optimal growing conditions that must be ensured for the plant. And this is when the akadama comes to save our lives.

Autumn bonsai. Photo by Jennifer Boyer


The orthodox and book definition would be: A granular clay whose origin is volcanic and found only in Japan, the place where the art of bonsai was born. The real consequence of this definition is summarized in:


Yes. So clear. It is one of its great properties that make it possible for us to grow bonsai in almost impossible places. Both in climate and soil. And we say climate because that balance of water and aeration added to its structure per se , allows to grow certain species in climates where they would not normally grow thanks to this retention of moisture and porosity. It is an expensive substrate but is used regularly by those skilled in the art.


There is controversy as to whether using only akadama substrate is convenient or not since there are a string of detractors and critics who say that this substrate lacks enough nutrients and others who have been able to grow on 100% akadama substrate. For this reason, recommendations for mixtures with other elements such as Kiryuzuna and Pomice are usually made. Let’s look at the differences slightly.

  • Kiryuzuna: It is a zeolite with great water retention capacity and slightly acidic, with a certain contribution of iron and recommended for conifers.
  • Pomice: It is the well-known pumice stone. As an structural element, it is interesting to mix it with akadama since it is very porous and light, but it is not the same as akadama in terms of degradation. The akadama will tend to deconstruct over time and the pomice will remain intact, thus helping to maintain the porous structure of the substrate.

The percentages are already a matter of alchemy and each species will require one or other mixtures. In addition, each teacher has his booklet and there will be people who use 100% akadama and do well and others mix 80-20% with Kiryuzuna … it is a whole world and the best thing is that each one finds their balance starting from certain bases already established as correct . If very controlled and methodical fertilizers are not going to be made, it is usually also mixed with peat, since with this material we also provide organic matter although it acidifies the medium a bit.

Peat field


For years and years of bonsai this substrate has been used but like everything, it has its detractors and its unconditional lovers. Each one has their own arguments and there are indeed those for and against. We have already seen the properties and what it is usually used for. Let’s now see the problems that this substrate can cause.

The arguments for or against this substrate depend on many things. First of all we have to think about the bonsai environment , especially the climate. A subtropical climate with high humidity, high annual average temperatures, with little or no frost, is not the same as a continental climate with cold winters and very extreme summers with a generally dry environment. This greatly conditions the growth of the plant and some conditions may be favorable to one species and others less.

But can climate affect something as “inert” as a soil? Inert we put it in quotes because of inert it has little in reality. But in this context the term fitted for the explanation to come.

Macro photo of akadama. Photo Abelard Uribe



Let’s think about water and its physical properties that they teach us from school. What happens to water when it freezes? Most obviously, it changes its state to solid. And what happens to its volume? It increases considerably . We already know what happens if we put cans of soda in the freezer and we forget to take them out …

This increase in volume has specific consequences in the rock that are highly studied by geologists as an erosion process . And it is this process that literally crushes the akadama. Remember that it is a granular clay and that means that it is very porous. Water enters these pores, hence its retention capacity. When frozen, the pressure exerted by the ice in the pore space breaks the structure of the akadama and literally turns it into clay powder.. This after 2 or 3 years, in winters with heavy frosts, completely destroys the good properties. The akadama forms a clay substrate, which retains water but does not aerate, cakes and puddles, putting so much effort into our bonsai. Resume:

Akadama pores with condensed moisture due to lowering of temperature -> freezes -> pore water freezes -> increases volume -> structure breaks up -> asphyxiating clay powder for roots in the medium term.

Note: In dry frosts (with low ambient humidity) this happens to a lesser extent. Freezing freezes, but the amount of water is less. In any case, there are many species of bonsai that we must protect from the rigors of cold during winter and in that case the akadama will last longer without degrading.

Even if there are no frosts, the degradation of the akadama ends up happening and it is recommended to transplant it in optimal conditions every 4 or 5 years.


The state of the art about akadama nutrients is broad and divided. Many say it has no nutrients. And we have come to see YouTube videos in which it is shown that it has a lot of iron because you stick a refrigerator magnet on it and beads of the substrate remain stuck. But is that iron 100% available to the plant? Usually not. That is why iron chelates are used in agriculture and not nails scattered across the field. Apart from home tests, what can be said about volcanic gravels in general is that they have some, not all, macro and micronutrients such as certain amounts of iron, phosphorus, magnesium or calcium in the form of oxides of these elements. Hence, since they are the only possible substrate for a bonsai, it is a lot of risk if subsequent subscribers are not made in a very methodical and supervised way. The akadama does not have a contribution of organic matter, which will have to be given to the tree at some point. Hence the above mixes are interesting.

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