Adam's Art and Bonsai Blog

Akadama, the ideal Bonsai soil





Soilless mix.

Whatever you call it (the only correct and descriptive phrase is the last one), it’s a controversial subject. One can have a more civil argument discussing the left/right division in the US political paradigm of contemporary society than you can talking about Bonsai mix. Sounds like a good topic for the blog, right? Yeah……

I will only, briefly, touch on the technical concepts I’ve discussed before (there are at least three or four previous soil posts here, here, here, and here), leaving the bulk of the data and science in those other posts, but the basics will be covered. I’ll try to be accurate to actual science but I’ll still be roasted by the true believers out there (I call them the Gatekeepers of the Status Quo, among other things). But I can handle it, I live by a motto “I am myself, for that I came”.

Let’s begin with some fundamentals of what a plant needs in the root zone. Here’s a basic breakdown: water, air, structure, nutrients. According to soil scientists, the best make up of a soil is 45% mineral/inorganic, 25% air (yes, the spaces between the particles), 25% water, and 5% organic. How I synthesize this for Bonsai, you need four particle characteristics in your mix for healthy trees:

Beyond being the correct size (from 1/8″ to 1/4″ or, for the rest of the world, except for Liberia, the USA, and Myanmar, 3-6 mm) we need particles that:

– break down

– that don’t break down

– that hold water

– that hold nutrients

Let’s discuss.

A particle that breaks down, fractures, erodes, wears down etc. This is important because roots need something to adhere to and crush (say that in your best Arnold Schwarzenegger voice: TO CRUSH!!!) It’s just an example of the Metal nature of Nature. It’s about entropy, degradation, the transformation of one thing into another. Some examples of this would be bark, horticultural pumice, horticulture charcoal, perlite etc.

Next, a particle that doesn’t break down. This is important for air capture between the soil particles, and to have structure for those roots to grow between. Air is important because it’s not water in liquid form that plants use but as a gas as it evaporates. It’s a gas exchange process in the roots.

Next, a particle that holds water. I think this is pretty obvious. Rocks like scoria or expanded shale hold almost no water (though it will hold water within the structure through surface tension). Clays, organics, pumice, etc do this well.

Next, a particle that holds nutrients. This is a concept called cation exchange capacity (cec). Now, this concept is misunderstood a bit. When talking about nutrients, there’s surface storage (think of a puddle…scoria and pumice have porous holes in it where nutrients can pool), and CEC. Cec is an electric charge where the soil particle is negatively charged and nutrients are positively charged, holding the nutrients to the soil. When you water, the positive particulates in the water make the nutrient available to the plant. This cec concept is important in our coarse soil, for as much as 80% of fertilizer just pours through the drain holes in the pots. You need something to catch it before it’s gone. Cec!

So, with all that, let’s address the title.

Akadama is the ideal soil component for bonsai.

Akadama is an andisol (andosols) or andic soil. In USDA soil taxonomy (the naming of things), andisols are soils that are formed in volcanic ash and can be defined as soils having high proportions of glass and amorphous colloidal materials, including but not limited to things called allophane, imogolite and ferrihydrite.

Colloidal means the molecules are dispersed evenly in a suspension or matrix.

Allophane, imogolite, and ferrihydrite are all very useful minerals or mineraloids, from industrial, medical, and, for us, soil, usage.

Ferrihydite is where we get the orange-ish color.

But all those 25¢ words don’t mean much really. It’s like when the bonsai snob uses Japanese words to describe something, like nebari (root base) or ume (plum) or soji (removing the top layer of soil and refreshing it with new mix) or what have you. Let’s break it down (no pun intended):

Akadama holds water, it holds nutrient, it breaks down, it has structure. An ideal particle of dirt (Yes, my friends, Akadama is technically dirt. I’ve seen it with decaying roots and leaves out of a new bag). It is mined in Japan and is literally dirt cheap… Japan. That’s what makes it ideal as well, for the Japanese. So let’s add another characteristic to my criteria: cost (which, if you are economically literate, translates to availability; the less available a thing is the more expensive it is….Supply and demand)

So, here’s the deal….some people say that we must use Akadama (or, as I’ve seen it recently, akedama….potato/potaaato I say) because it’s the best dirt to use……meh. If that were the case, why was the Aoki mix developed (pumice, river sand…which is a lot like stone or expanded shale, scoria, and Akadama)? Interesting question. Further, in southern Japan, where the Japanese black pine are farmed, they use about 100% scoria (you ever see a Christmas tree farm? Imagine that, but they’re all informal upright bonsai trees, ten dollars each!).

This is the aoki mix.

I like it. But I don’t like the fact that it is surface strip mined out of the sacred cryptomeria forests in Japan, dried, mixed, bagged, and sent, literally, halfway across the globe to be used by asshole me, a crazy, snooty, bonsai guy in Florida.

Here’s my mix:

I see a cat….

We have…..pumice:For water retention, structure, and crush-ability.

Scoria (red and black, just for fun) For structure and minor water retention..that’s the red flavor above.

Expanded shale and or slate (what I have available, I’ll use both)

It’s for structure without water retention (it rains a lot in Florida,it’s all about drainage here).

Charcoal, used for its mild cec, it’s water retention, it’s attractiveness to microbes and it’s crush-ability (it used to be thought that charcoal doesn’t degrade, as there is evidence of hearth fires from the Paleolithic ages, but recent laboratory experiments show that it does, and the thinking is that it is the charcoal, in nature, being concentrated in a singular spot, by either rain or human activity, that slows the amount of degradation occurring).

The roots love charcoal by the way. Charcoal attracts mycorrhizae.

And the last is called NutraAgg by the American Bonsai tools guys. It’s a naturally mined product that is almost miraculous in its water retentiveness and Cec. It’s used on golf courses to save on watering and excess fertilization, it’s local, stable and it works.

It holds water, nutrients, and degrades slowly.

My mix ratios, and this is my new mix as long as I can get the components, 2 parts scoria, 1 part shale/slate, 1 part pumice, 1 part NutraAgg, and about one part charcoal.

I call it the SuperMix.

I like to think of it as a standard mix that can be added to or taken away from for a particular tree, say….add some composted conifer bark for added microbial colonization and cec, or adding kanuma (a highly acidic pumice from Japan. And there isn’t a real replacement for that I’ve found.) We use it on azaleas and other trees that need high acidity to process nutrients (Look up the ph a blueberry needs!).

I sift out most of the fines, but you can adjust your particle size down to 1/16 of an inch and use it for trees needing more water (the smaller the particle size, the more surface tension act in keeping water molecules higher in the pot).

You can also add moss to the top of the soil for that.

That’s a water jasmine in Winter Silhouette. They need lots of water.

The ratios are important because if you have too much, say, charcoal, it creates an imbalance and you could have too much of certain microbes, like mycorrhizae, and instead of helping the tree, they smother it. Or too much pine bark, or Akadama or turface, or NutraAgg, it holds too much water and fertilizer, and you get growth when you don’t want it (say in January in Florida with a trident maple). Or you have too many “structure” particles, like the shale or maybe decomposed granite or chicken grit. If you’re in Arizona, you’d need to severely change my mix to suit the hot/dry environment you’re in. Or the wet/cold environment.

Where does this leave us in the “Bonsai Soil Wars”? Well…….I have put forth some science, in this post and the above linked ones, I’ve stated my preferences and reasons for them. I don’t argue, because it won’t change closed minds. If you really look through those previous soil articles, you’ll see I’ve changed my mix a few times.

I don’t use conifer bark because of availability, the brand I used, Fafard was purchased by another company, and they phased out the small sized, composted, ph balanced product I prefer to use. So I use charcoal and the NutraAgg.

I don’t use calcined clay (turface and other brands) anymore because the particle size got too small. I was discarding half the bag after sifting.

I tried diatomaceous earth, it’s worthy, but only in the correct percent (15-20% of the mix. Any more and you hold too much water).

I’ve tried LECA, crimson stone, Grow Stone, and just about everything else. Yes I’ve used Akadama. All of it works. And to tell you the truth, which I try to do, you can grow bonsai in broken glass, if you learn the hardest lesson there is to learn about bonsai. A lesson all the Soil Warriors ignore because they are RIGHT, by god, and you are WRONG!

That lesson is….Da Da Da Dum!


I have many examples of trees planted in the same mix, are the same species, right next to each other, and dammit if one uses water more than the other. This is the secret to watering:

Each tree needs a differing amount of water at different times of the day, the month, the season, and the year of development/repotting stage.

And that’s the lesson in soil components. It’s ok to use a standard mix, be it Aoki, Brussels bonsai, American Bonsai tools, or my aptly named SuperMix. Or make your own. Just adhere to the particle requirements and you’ll be ok. It doesn’t matter what Joe Blow in California uses, or Jack Off in Alabama says that all the professionals use, or what Georgie Porgie up in New York has used all his life.

Just learn how to water it, and you’ll be fine.

But you can’t argue about that now, can you? And there’s no better joy in the world for the keyboard warriors like a good social media argument where they throw up all the memes and gifs they’ve been fiendishly hoarding in their smart phones, and the gratuitous appeals to authority reasoning, the name dropping (make sure you tag them so they know who you are), and the kow towing, sycophantic sleaziness.

Sorry, I got carried away in my prose, it won’t happen again… this post, at least.

To quote Shakespeare ” Cry ‘Havoc!’, and let slip the dogs of war!”