Soils - Bonsai Block (Calcined Clay)

In the soils stream, quite a few asked about using diatomaceous earth in lieu of akadama. Has anyone tried Bonsai Block (Calcined Clay)?

I’m not familiar with that product myself, but it looks to be fairly expensive. You can currently source Akadama for less money.
I have had good luck with diatomaceous earth. $10 for a 40lbs bag of SafeTSorb. And I can get a little for than 50% usable grain size.

Im currently buying all my soils online. I can’t see to find a local source.

Calcined Clay is also referred to as Turface.

Our club uses it in their mix in lieu of Akadama. It is usually a very small soil particle. It has good moisture retention, and a decently good CEC. I have used turface in soil mixes before, but I find better results just using the normal Boons mix with no substitutes.

The big thing with calcined clay is that it is readily available and cheap when you buy the “non-bonsai” stuff. Unless you can get it super cheap, I wouldn’t use it. From the looks of the cost of Bonsai Block, I would just use Akadama.

But if you are experimenting, I say go for it!! Then you can let us all know how it went.

I think Ryan explains why Turface is not a good choice of soils components in the stream. I know Akadama is a issue even Mirai is looking to find local replacements.


Hello All,
I have been using DE (Diatomaceous Earth) for several years, since 2010 as best as I can remember. I have used it alone and with other substrates as a component, my favorite mix for central Texas is 50% DE, 20% lava, 20% pumice, 10% pine bark. The DE that I source is from Napa Autoparts and is the #8822 also known as “Oil Dry, Oil Absorbent, Floor Dry or Super Absorbent.” It seems to hold up very well, 3-5 years depending mostly on weather conditions. It is super light weight and a bag is about 6-7 gallons in volume prior to sifting and costs about $11 per bag. After sifting out the fines I usually end up with about 5 gallons worth of 1-3mm particle size substrate which is great for me as I like the moisture retention for the dry heat. I have never had any particle larger than the 3mm screen I use for sifting so I use a "aeration layer consisting of lava/pumice or lava/pumice/pine bark. Hope you all have a great spring potting/repotting! Let me know if you all find any other substrates that work well, Im interested in replacing the pumice with something else as its expensive and I would love an alternatve.


EP minerals also makes Blue Ribbon Cat litter which a DE product. It seems to have a much higher percentage a useable size than some of the other products. at about 43:08 Ryan talks a little about clay as a bonsai substrate. I remember Ryan speaking specifically about Bonsai Block I believe during the soils stream and advising against it, advocating for DE instead.

1 Like

So…here is the nitty gritty on Calcined clay, Turface, and Akadama. Ryan probably does not get into this because he is telling you what works and what will produce the best trees, and he is right. Here is the reason why he is right.

Where are they getting this clay to make this supposed “high fired” clay. I do quite a bit of ceramics and I know “high fired” means the clay is fired to the point that the clay becomes impervious to water. It was a huge advancement in ceramics when it was invented. So, the clay is actually low to medium fired. When a clay is fired, it also changes, because the minerals in the clay react with each other.

Akadama is not fired. It is deep clay that has gone through the processes of compaction, consolidation, and to a point lithification. This is why there is soft and hard Akadama. They scrape mine the clay and then the particles are left out in the sun to dry. The deeper the clay is, the more these processes make the clay harder and less acidic.

The clay that is used to make Turface and like products can come from anywhere, and more importantly, any depth. Shallow clay is acidic. Deeper clay where Akadama comes from is more neutral. The intention of these products is for ground soil amendments or clay surfacing, hence Turface. I do use Turface in the ground when growing bonsai. It does promote small root growth near the trunk. I also sift it and use it in pots for some deciduous trees that can handle it if the clay is acidic. I do not use it on conifers because the particles are to small and flat which impleads air entering the soil.

Here is the nitty gritty on Akadama. It is really unremarkable as far as clay soils go. It is 1/6 iron oxide(rust), 2/6 aluminum oxide(that white powdery stuff that can be seen on aluminum wheels when not cleaned, basically aluminum rust) , and nearly half silica or sand. There it is, these components can be found in most red to brown clays. BUT…the ions from these components do help nutrient transfer. That is why all good top soils and potting mixes have some clay in them for this very reason.

SO…the real question should be, can we make Akadama? It is just compressed clay. This is not rocket science. I know this because I worked for NASA when I was in Air Force Space Lift. Not even close. Maybe it can be made better by adding other minerals. What minerals you ask. Great question.

Something to ponder on.


This is freaking fantastic information. Thanks a ton for the input!

Edit: Question then, what is it that makes the Akadama have the quality that roots are able to grow through it? Silica sand doesn’t have that quality, so what about the process of “compacting” clay gives it the ability to then be “pierced” by the roots? That is what we really need, not every identical characteristic of Akadama right?

1 Like

Akadama has holes in it because of bio matter that has decomposed. Not every piece of Akadama has holes in it nor do I consider it to be a crutch factor for Akadama. Akadama is going to brake down anyway from being watered over time and roots compressing it. All natural things get broken down into their components over time. Just like steel, it rusts. That is nature breaking it back down into its’ components.

BUT, If one felt that this would be desirable, you could add fibers to the mix that easily decompose, and bam, you have holes.

I believe the positives of Akadama are that it is clay and its’ particle size. The ions in the clay help feed the plant. The larger particle size allows fresh air in every time you water. The larger particle size allows you to water more. Every time you water it is like flushing a toilet. The water lowers in the pot drawing fresh air in its’ place. That is a huge advantage, fresh air every time you water. It is also why a pot should always have feet and large drain holes. Air can not get in the pot on its’ own due to vaper pressure from the water. That is physics at work and why growing in a colander works so well. More available air/oxygen. It is also why feeder roots grow near the surface.

I was under the impression that a pot with only akadama gives the tree 100% of the pot to grow roots in. This is not the case with other soil components (Lava, Pumice, Turface, DE, etc.). This is what I thought was the defining characteristic of Akadama? Maybe I’m confused but I was pretty sure that was why it is so desired as a bonsai soil.

Then wouldn’t almost any other clay do the trick if that is what is desired? Large particled DE would do the same would it not?

Edit: What about things like Caliche which are clay (right?)

Sounds like you right here. As long as the particle size is right and the ion capabilities are there, it should grow good plants. Plants can grow in 100% pumice and use 100% of the space. Hydroponics growers do it all the time. Also Ph should be in the correct range for the plant.

I did forget to mention Akadamas’ ability to retain water. That is also key. What gives roots access to 100% of the pot is the presence of moisture and air. That is why top dressing the tree is important. Roots will not live near the top without retention of water. They will not survive at the bottom without good aeration. That is why I think Ryan is so right calling the bottom layer an aeration layer. This is also why pots need feet and as much drain space as possible. The more drain space, the more air can get into the bottom of the pot.

@ryan Says in the Soils stream that the problem with most clays is their plate-like structure.

Here is my rough quotation of him speaking on Akadama:

“Akadama’s structure is special. It has a tubular form which allows the root to enter the soil particle. As the spaces get smaller the roots get smaller with it and this allows the roots so still occupy the smaller air spaces between particles, this is what makes Akadama so very special.”

I think we might be missing a huge point somewhere…

He did say that and I think you are right, so if we were to make Akadama, the added fibers to make holes would be a necessity. Yes, clay formation is in plates because of the layering effect of soils. I do have my doubts about this being a needed attribute because the roots do eventually get bigger and break the particles. However, those small areas/tubes would attract water through the capillary effect and increase water retention. I guess I could go both ways on this.

My guess is that this Akadama clay was formed from a slide of some type which mixed it all up. If we make our own, we do not have to worry about that because we would have to mix it like ceramic slip then pour it on a plaster slab to suck out most of the moisture and then compress it.

Good info here. Keep it coming.

I’m sold on Akadama. Likewise it would be good to find local equivalents

On reviewing Ryan’s comments re on the Soils video, he outlined a crucial point: that not all Akadama commercially supplied in Japan is the same quality

Some Akadama is fired, at a specific temperature so that it doesn’t decompose too rapidly. It will eventually though breakdown. While other Akadama isn’t fired and consequently turns to dust in a shorter period of time. And some Akadama isn’t fired and suitably maintains form. An ideal Akadama quality would be one that can continue to hold some degree of form for up to 6 years, allowing more establishing/ maturing eg coniferous bonsai material, to remain in their pots longer because their roots are not being suffocated of oxygen and water problems because the substrate hasn’t compacted. By a generic 6 years, it should be truly time to trim roots*

I’d like to know what the ideal firing temperature is - could home gardeners do this in their ovens at home. Thought: perhaps the firing process contributes to a higher cost of commercial product, consequently limiting access to some bonsai artists budgets

I have been using/ experimenting with diatomaceous earth (diatomite) for approx 3 years. Primarily because Akadama has not been readily accessible. The quality of the unfired diatomite batch I accessed has held form consistency. However, I have heard some bonsai artists in my region have accessed fired diatomaceous earth (no idea where from yet; product is really doing its job well), while others seemed to have accessed a low grade quality/ unfired diatomite which has decomposed too rapidly and they have written off diatomite altogether/ are now striving to import Akadama (though they may find too they get an unstable Akadama as many qualities/ differing batch qualities are on the market)

*for younger bonsai plant material in early development, a repot might be eg every 2 years, so if a diatomite batch holds its form for that period it’s relatively doing its job. But in Ryan’s Percolation video, he showed that organic matter/ decomposed substrate material near the [ “sheen” ]/ root heart straight under the trunk, was de-oxygenised water-logged muck from the original central rootball ie that integral soil ball that you don’t touch in repotting. Requiring him to do gradual soil replacement “operations” over the following repots, taking literally years to correct. So, if you can avoid applying crappy quality substrate material in the first instance you are setting the tree up for future success ie future-proofing