Is Lava Good For Bonsai?

This is a legitimate question. My master Shinji Suzuki never used lava (aka scoria), preferring just akadama and pumice.

On coming back from Japan in 2006 I continued using the akadama / pumice mix and have always had strong, fine root growth with dense root masses.

Several lava stories have stuck with me over the years. Joe Harris III reported very high levels of boron in lava at Iseli Nursery in pots with poor root growth. David DeGroot then had root growth issues, and a lab found what they called “toxic levels” of boron traced to the lava in the mix. Mr. Suzuki’s simple akadama / pumice mix has served me well and these stories don’t warm me to lava.


Lava, aka scoria, commonly used in bonsai media

Last year I was in conversation with my former apprentice Andrew Robson who does a lot of traveling and repots more bonsai in various soil media than I do, and he’s developed negative opinions about lava, particularly red. Here are Andrew’s observations:

As a bonsai professional who travels to work with students across North America and with a large collection of my own, I end up repotting several hundred bonsai each repotting season. One thing I’ve noticed is the effect of different soils in different locations across North America, and with different skill sets. While the professional bonsai community has come to the consensus that volcanic soils work best in a bonsai pot for optimal root growth, I’ve observed that lava grows worse roots than pumice and akadama alone.

I don’t utilize lava for many reasons, but the first and foremost is the root systems I routinely see in it. Almost without exception, every bonsai I’ve repotted where lava made up at least 30% of the soil mix has had poor roots. Oftentimes when I take these bonsai out of the container, much of the soil just falls away because there isn’t the fine root mass to hold it all together. In my experience, and now the experience of my students and clients, lava isn’t creating the root systems that we’re looking for. The same exact bonsai, switched to an akadama and pumice mixture, grows roots that are far superior in a much shorter period of time.

There’s a few other reasons I can’t stand working with lava. Other than the poor root growth I see in it, it’s extremely heavy compared to the alternative (pumice). It can add a lot of weight to a bonsai pot, especially a large bonsai. Lava is also hard and will destroy the sharp edge of bonsai tools with just a few repottings. Plus, it’s one more material to source, purchase, sift, and mix up for our bonsai. For all these reasons, I avoid lava with a passion.

Year after year I continue to see the same thing as I repot bonsai across North America: poor roots, heavy trees, and dull tools when lava is over-utilized in the soil mix. Many of the top bonsai gardens in Japan go without lava for some of the most valuable bonsai on the planet, and if those trees can thrive without it ours definitely can as well.

If you take your bonsai out of the pot after many years and all the soil falls away, or you cut the circling roots and all the soil falls away, it’s probably not a soil mix that is working.

I always encourage bonsai practitioners to keep doing what is working well for them even if it’s not something I teach or practice. But over the last several years I’ve moved away from using lava in my own and my student’s bonsai pots, and we couldn’t be happier with the results.

—Andrew Robson

Andrew’s findings are documented in this video (sorry, may only show on a desktop version):

As an aside, Mr. Suzuki used 2/3 akadama, 1/3 pumice (kiryu), similar to what many other Japanese professionals use. (This proportion of akadama is prohibitive for many Westerners. I use 1/3 akadama, 2/3 pumice for conifers, and 1 / 1 for deciduous. Most of this has been an economic decision based on the expense of akadama. I’m exploring 100% pumice as it is cheap where I live, and find very good root growth, though the root structure is different than in akadama. I’ll report in another post about that.)

Lava, however, may create anemic root structures. The source of lava may well be implicated here, some perhaps problematic and others benign. Sometimes it creates good root structures, other times poor. If your source is working for you, use it. If not maybe compare to pumice some year.

Lava can work—a few nurseries in Japan use it in high proportions, but those are the exception. In Indonesia it is often the major soil component. Here in North America I have my doubts all sources are safe. Much of the observations of Andrew come from Texas and the Midwest, and I’m not sure where that lava is sourced from.

That some sources of lava are OK doesn’t move me to be unconcerned. Given the lab results we have and the pure empiricism of Andrew’s findings (and my own observations over the years), this seems worthy of a conversation and more testing.

Please read through the comments, as many have raised points that are worth exploring. I wish to state clearly: if you have a source of lava that is working for you, creating the fine, solid blocks of roots that Andrew’s video shows, then keep using it. This post is meant to raise a flag of warning that lava may not be as predicable as pumice, which is its closest alternative.

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  1. Peter Buckley says:

    So do you use a 50/50 mix?

  2. Joe Noga says:

    What is the suggested proportion of pumice to akadama? Do you use this same mixture for deciduous and conifers using the same proportions? Do you see a difference in watering now that there is no lava? What other professionals in Japan use this mixture other than Shinji Suzuki?

    • crataegus says:

      Hi Joe, I just put my thoughts about that at the end of the post. The last question, about how many use just akadama / pumice, I am not sure of although I do know Suzuki is not alone. If used, lava is often just a sprinkle in the mix.

  3. Michael says:

    Thank you for this valuable tip!


    I think this is the key phrase for those of use who refuse to, or can’t afford to, use akadama:

    “when lava is over-utilized in the soil mix.”

    • crataegus says:

      It might be. But, I’ve been exploring 100% pumice and find never does it limit root growth, whereas 100% lava often does. So… I am unconvinced it is doing anything useful in a soil mix. Maybe lower percentages of it create good structures because the proportion of lava is so low that it doesn’t register.

      • Roger case says:

        Although a bit off topic I use 100% pumice to start all my cuttings and it produces good rootsge – which tends to suggest its use in bonsai soil is a positive – combined with akadama which has good cation values as well as other good properties it appears these two components form the basis of a good bonsai soil
        What then does lava offer that a bonsai soil need?
        One idea might be that unlike akadama and pumice to a lesser degree it does not break down over time and may provide a bit of a matrix for the other components to exist in rather than become more clay like and dense – and remember akadama is a volcanic clay

  5. Mert Çiftdemir says:

    I agree with your thoughts about lava. What about extended clay and grounded tile particles?

    • crataegus says:

      I don’t find these to make very good root structures. But, in your own situation, I would try pumice and compare it to those. I’ve seen some pumice sources be very hard and lack the light, gas-and water-exchange properties that it’s known for. So, success is often based on what we can find.

  6. Victor Taboada says:

    Food for thought…so you wouldn’t use Aoki blend either, right? I understand that it contains some lava.

    • crataegus says:

      I have used Aoki blend and find it to be pretty good. The lava proportion in that is fairly low, a sprinkle, with a high proportion of akadama. That might be why.

    • Andrew says:

      Hey Victor, I actually use aoki regularly and like that mix a lot. It’s ratio is 80% akadama, 18% pumice and 2% lava.

  7. Victor Taboada says:

    I see different options in the US for pumice…do you have a preferred source for your pumice? Is it all the same?

    • crataegus says:

      Good point Victor, there are different sources with different characteristics. Pumice is known for it’s lightness, which translates to water- and gas-exchange properties. Some sources—-I’ve seen this out of Utah—-are very heavy, lacking this. Much of the pumice in Japan is heavier. The pumice I use comes locally, from the Pacific Northwest. It’s light, off-white, and consistently creates good root structures.

      • Dan kofford says:

        The pumice your talking about is not from utah it is out of Idaho “Hess pumice “

      • crataegus says:

        Thank you for the correction! Idaho, yes.

      • Dan kofford says:

        Utah has lava fields and I have not had any issues with my trees 🌲 I only have collected conifers and find the 1 to 1 ratio works very well how how ever it Do use a humate soil conditioner from time to time

    • Andrew says:

      Hey Victor,

      Perlite is also something to consider. It’s the industrial version of pumice, and I use it on bonsai that take more than one person to move to reduce weight and dry out the massive pots faster. You can mix it in with your pumice or use it as a 100% replacement. It does float, but that’s why we use top dressings in bonsai.

      • crataegus says:

        Perlite is superb. I love it in nursery pots growing young plants in particular. Agree with Andrew that in a bonsai pot it needs a top dressing. And chopstick lightly as it is easily crushed.

      • Victor Taboada says:

        Perlite is way cheaper than Pumice, yet I feel that it retains way too much water. Every time I have used Perlite and done repots I find the Perlite too soggy for my taste, which doesn’t happen with Pumice.

      • crataegus says:

        It does retain a lot of water. Gets very heavy. Then very light. It’s great for nursery stock. Pumice is better I think in a bonsai pot but then many don’t have access to pumice.

  8. Bob Boyd says:

    Another standard bonsai practice shot out of the sky like a balloon. As if bonsai culture isn’t already leaning heavy toward elitism, another cheaply sourced soil component tossed out in favor of the most expensive soil component. I find it hard to believe that on a planet created by volcanism, the only place akadama can be commercially mined is on an island in the western Pacific. I would like to hear from more bonsai professionals before I throw out my bags of lava. Also would like to see scientific data documenting the benefits or non benefits of using or not using lava.

    • crataegus says:

      Thanks for the comment Bob, I’d like to see some other sort of documentation too. Though, at the end of the day, the volume of trees I work with, like Andrew, has answered this question for me.

      There is akadama in the Pacific Northwest, but mining it is an expensive proposition. Pumice may be just as expensive based on where you live. Some sources of lava do not seem to present a problem and may be much more inexpensive, again depending on location. Lava is still better than many alternatives, but this article is just comparing it to pumice.

    • Bob I wouldn’t say this post is arguing for more akadama use. Really it’s arguing for more pumice. Most professionals I’ve heard of in the US use akadama/pumice/lava in equal proportions for Deciduous. If you put akadama in the more water retentive (organic origin) category, pumice and lava fall in the aeration and inorganic category. Thus in the basic principles of air and water, removing all the lava and adding additional pumice to the soil so the overall organic:inorganic ratio does not change would be more like what Michael is suggesting here when he mentions his soil mix at the bottom.

      Also if you want to use an akadama substitute, Dan Robinson uses fir bark as the water-retentive side of the equation. I just posted a blog article on my website which shows the result of using this bark chip/lava/pumice yielding dense fine roots.

      • Ryan says:

        Ahh sorry typo, I’ve heard of akadama/lava/pumice in equal proportions for conifers/dry-loving species (2 parts aerating components, 1 part water retentive) vs a 1 part aerating component : 1 part water retentive component for Deciduous. In the latter thar can be 2 parts akadama and 2 parts pumice or 2 parts akadama and 1 part pumice + 1 part lava. Mix and match components as you see fit in your own experiments!

  9. Ray says:

    Interesting, I have not had the same result. Trees are packed with roots and trees are healthy. I do agree that it’s not great for sissors.
    But I haven’t seen those results.
    What will the world do when akadama runs out. The one thing for sure is that pumice will pretty much grow everything.
    Just my results here. It could be the heavy rainfall we get here.
    I will try it on my spruce this spring as a test.

    • crataegus says:

      You likely have a good source of lava then. I don’t know many hobbyists who are testing their source for toxicity. Just seeing if it works for you and creates good root structures should be good enough. This post is meant to raise a flag of warning that lava may have problems from some sources. I’ve never seen or heard of a problem using pumice.

      • Ray says:

        The source we use here is from lava can company and is used in aquaculture. They have done the testing to make sure there is no damaging elements in the rock. It is sifted and cleaned to 1/8- 1.4 in sizing. It’s possible sources for others could contain some toxic natural chemicals.
        I agree with you on pumices root creating abilities. It is an amazing volcanic material.
        Thanks Michael

  10. Graham says:

    Lots of good information. Maybe it’s the brand of Akadama I purchased but it gets soft and breaks down quickly with all the rain we get. Use black lava as a top dressing for appearance only (covering the whitish pumice).

  11. Peter Calandrini says:

    First I would like to thank the very good article for the line of reasoning. I spoke by e-mail with Mr. Yajima who uses a lot of Amagi (red lava) in the initial fattening increases and he has shown excellent results, especially in small sizes. I was seeing that depending on the requested location there is more enrichment of heavy metals, geological factors, and the increase of aluminum that perhaps with greater acidity is transformed into its exchangeable form that castrates cationic exchanges.
    thank you very much for the article!

  12. August Day says:

    Disappointing news to say the very least. Agree with Bob Boyd above totally. Is this the real deal or just a promotional gig for ackadama? Definitely need the science guys to chime in here verses opinion from just one guy, and I don’t mean to imply that he is not correct, but we certainly need some back up before we all start pitching the lava and wondering what we use in it’s place.

    • crataegus says:

      Not promotional, I don’t sell akadama and I’m trying to move away from it due to its expense. Pumice is the alternative. In many cases lava seems to work; it’s that sometimes it doesn’t that makes me leery of it. If it works for you, and you’ve compared it to pumice, then keep using it.

      • August Day says:

        Michael, Sorry, I did not mean to imply that you or Andrew were promoting ackadama, but I can see that you would take it that way. I do think that more info could have been introduced from wherever backing up the poor results for lava before this article was published. August

      • crataegus says:

        All of this is anecdotal—like in Andrew’s video. This is what Andrew and I are seeing again and again. I’d love to see more info, but this is what I have to offer.

        As I state in Bonsai Heresy, there is often very little if any scientific evidence to support what we do and need in bonsai, and there is a gulf between our needs and what general horticulture needs in a nursery pot growing a young plant. But I’m also in agreement with you—I’d love to see some studies, confirming or denying. But they’d have to be long-term studies in bonsai pots, not some abstracted thing that doesn’t relate to how we’re using it. For now, we may need to discuss anecdotally, unfortunately.

      • August Day says:

        The chart that shows mineral content is interesting

      • Jim Horton says:

        Thanks for the article, Michael. Coming from the world of medical devices (i.e. proof-driven), I have no problem with how this article is written. It’s no different than publishing results from a small, multi-site study. You and Andrew combined have enough observations of the issue to allow for a statistically significant conclusion. Let others with a similar level of observation weigh in if they see results to the contrary.

      • crataegus says:

        Thanks Jim, I appreciate your comment and the invitation for others to weigh in.

        I wouldn’t be surprised if many say they have good results with lava. My suspicion though is that with time and more comparison with pumice some may find their lava underperforming. That doesn’t mean all lava is bad. But raises a thought bubble that some sources may be less than ideal.

  13. Mats Hagstrom says:

    From a previous podcast you know Jonas Dupuich has more positive experience with lava. As was mentioned in the podcast it may not be as simple as saying “lava is bad”.

    Each soil component can have drawbacks. Pumice varies wildly from batch to batch depending on how and where it’s mined. Likewise lava has many personalities with different properties.
    I find anecdotal evidence tends to not be very accurate when observers start by having a clear preference or bias. Perhaps it isn’t so much the soil as it is the soil plant variety combination that should be evaluated. Lava does have a unique appearance which can at least aesthetically have a certain impact that can potentially be desirable by some.

    The horticultural commercial industry seems to certainly loves perlite a whole lot more than lava. It’s repotting season (still) perhaps I’ll try a few young plants in lava vs pumice mini experiment.

    When working with something as complex as bonsai there are so many variables. This can make it challenging to isolate individual variables when there are so many other confounding and cofounding both obvious and unknown.

    Making definitive statements based on observation should be done with an understanding that these may be opinions rather than fact. Not making statements based on observation withholds potentially vital information and stifles the community from learning.

    Last year I put several trees in 100% lava. One was a collected Ribes aureum var. aureus. It seems to have done well having been transplanted in pure lava so far but alas I have no comparison.
    Michael, thank you for a well written and though provoking blog.

    Mats H

    • crataegus says:

      Thank you Mats these are very fine points. As I often do, I’ve added things to this post that reflect the comments. My observations and Andrew’s are pretty broad and are not based on a few plants but, combined, two decades of repotting experience after beginning to use volcanic particles. The use of volcanic materials was radical three decades ago. It was a huge step, in my opinion, in the right direction.

      Do we perhaps need more nuance to our understanding of the three main particles? I think that may be the question, and our situation and the source of the particles we have may change our experience with root growth in our pots.

      Anyhow, thanks again for a thoughtful response!

  14. treetroll1 says:

    Well this is surprising news – not something th

  15. treetroll1 says:

    Is leave now not used for any of your trees?

    • crataegus says:

      I have occasionally used a sprinkle of lava—-less than 2%—-for conifers. But, I have no evidence for or against adding such a small amount. In general, no, I don’t use lava in my mixes.

      • Victor Taboada says:

        Michael, if keeping lava out works for Shinki Suzuki that’s saying a LOT!

      • crataegus says:

        He’s not alone in doing that. But then some in Japan use 100% lava, which means to me they have some good sources there. Also, Indonesia. Not all lava is alike, is I think the takeaway. That some sources promote good root growth doesn’t pacify me with the fact that some do not promote it. More testing of lava I think is in order.

      • Victor Taboada says:

        This posting sure touched a nerve! Thank you Michael!!!

      • Victor Taboada says:

        In this great video from Hiroaki Suzuki (Shinji Suzuki’s son) working in the Suzuki’s workshop, you can see the type of soil used:

        If you go to the 16:30 minute, you will see that the soil mix indeed appears to be akadama/pumice…no lava.

  16. Joshua Kaltreider says:

    Fantastic topic! Thanks for sharing your observations. As someone learning/ practicing with a small personal collection, I simply won’t have the number of repots needed to make these deductions, in any reasonable amount of time. Yea the evidence is anecdotal, but it’s also invaluable for us practicing on smaller scales. I’ll be sure to bring these observations into my practice this potting season. Thanks again.

  17. David J De Groot says:

    My own mix that I use generally is 4 parts Kiryu (or pumice), 2 parts Akadama, and 1 part processed charcoal. If I ever get to the point where Akadama becomes unavailable or prohibitively expensive, I might go back to what we used in Louisiana in my early days with great success – a 50/50 mix of sifted pine bark and what we called Hadite (now Riverlite), a manufactured lightweight expanded clay. I believe some folks down there are still using it. No point in using Riverlite where we can get natural pumice, and we need more than 50% pumice for conifers in our climate of extended cool, wet weather. Pine bark is loved by plants but has two big drawbacks – the time and effort consumed in drying and sifting it (to get as little as 1/3 that is not either too big or dust); and the fact that it breaks down more quickly in the pot than hard Akadama. Just to complicate the conversation!

    • crataegus says:

      Thanks David for weighing in! Someday we’ll have to get around to chatting about charcoal…

      • John says:

        Wow. Amazing conversation but as you mentioned Michael there are a lot of ifs, ands, and buts here.
        Science wise I can see the higher proportion of pumice adding a bit more aeration and less weight.. (don’t personally. see dulling scissors as a thing as my scissors seem to get dull in both lava and pumice.)
        Dave is there any truth to you getting a load of boron lava at PBM years ago? Was it source specific? All former rumors seem track back to this event.(re email Andrew Robson).
        Also is there any side by side photographic data showing these differences in the tree roots.

        Frankly after alot of study I’m left wondering if the “issue” with these tree roots is partially a mistreating rhizosphere situation vs the soil mix? …and a layer dense lava just might enhance these hazardous chemicals stay times in our area? Considering the chemicals a great deal of folks use to subject their trees/ media might we actually be be focusing on entirely the wrong thing?

        Just a thought.

      • crataegus says:

        Hi John and thanks for the comment! On the desktop version you can see the video that I pieced together of Andrew’s findings. That’s the best ‘data’ we can offer of years of seeing these results.

      • crataegus says:

        Hi John, thanks for the comment!
        I spoke with David the week of this posting and yes, they tested all components of the mix they were using and lava came back as having “toxic levels” of boron. Joe did write me to confirm the lab tests had found boron, not so emphatic as toxic, but they were “high levels” in a mix that had poor root growth.

        It’s the comments from folks like Ed Imholt that I’m most swayed by, who has hundreds of plants of the same age, comparing root growth in pumice and lava, and him walking away from lava. This is just empiricism. It mirrors what I’ve seen for years, in lower volume.

        There is a need for tests to show us what’s going on here. Tests will help explain this one way or another, especially useful for those who don’t have access to hundreds of examples like some of us do. For practitioners like me, tests are admittedly secondary. It won’t change what I do as I’ve enough practical evidence in everyday observations. If I’m seeing soil with lava in it fall away from root masses after years in a pot, I’ll stick to pumice (and akadama, for now).

        But——very few see that volume of root / soil situations to convince without tests, and tests are in that case helpful.

        So it sure would be nice to know some of the answers to your questions! Perhaps you and others will do some tests? We could use some. And from different lava sources.

  18. Mitch Fennell says:

    I am not seeing the link for the video about the negative effects of lava in soil mixes.

    • crataegus says:

      Are others having this trouble? There should be a small YouTube video there, it may not open to a larger one.

      • nkoan says:

        The video didn’t come across in the email version of the blog post, but I can see it in the web version of this post.

  19. rick davis says:

    Strange — Almost everyone in Hawaii uses sifted cinder because it is what we have —and we have beautiful trees and good root growth …and pumice is lava just with more air pockets and our cinders are usually full of air pockets as well

    • crataegus says:

      Thanks Rick for the comment! Yes, in many places around the world people are using lava, often 100%. A few growers in Japan do this. Others in Indonesia. So obviously some sources of lava are fine. That doesn’t pacify me though about some of the problems I’ve seen and others have seen in root balls here in North America. Something is going on there, it may be boron, it may be something else entirely, but I hope we all stay a bit alert from now on and maybe do some testing. As I state at the end of the post, if you’re seeing good, solid root masses using a good bit of lava, then keep doing what you’re doing and stick with that lava source. It’s working for you.

  20. Post of video did not get attached.  Will look for

  21. Found it

  22. I used to use lava but ran into the same issues with poor root growth and development. I grow my seedlings in grow pots for a year or two before putting them in the ground to grow out. Growing in lava tended to have long stringy roots, whereas the once planted in high concentrations of pumice (70%) resulted in highly ramified roots and it speeds up the process IMO. I have found no benefit of using lava and therefore see no reason to continue spending money to add it to my mix. Perhaps the pacific northwest lava is of poorer quality than other regions, I don’t know, but I do know lava does nothing for my trees here at the nursery. Do I have scientific evidence? Nope, but the 1000 trees I have here at the nursery are growing great without it and thats good enough for me.

    I find it comical that people are saying they need scientific evidence before they will change their habit of using lava, but that argument works both ways. Where is the scientific evidence that shows it is great for bonsai? I think in the end one needs to use what works best for your trees and ask yourself the question why do you use what you use in your soil mix?

    Great post Michael, questioning the use of lava in bonsai soil mixes is almost “Heresy” lol

    Ed @ Copper Creek Bonsai

    • crataegus says:

      Thanks Ed for the comment—-yes, you’ve lots of plants there, and at the end of the day those many little not-quite-data points do add up, and are pure empiricism. Observation. But also that you may have had a lava source that has this as yet undetermined problem—-maybe it’s boron, maybe it’s something else, but it still is the same observation, that pumice and not lava has given you better root growth. And that adds to the conversation.

  23. Don Barker, P.E. says:

    Thanks Michael, I have noticed the same empirical evidence that you and Andrew discuss in the article above. Through my first years in bonsai, I used the standard mix of 1/3 akadama, 1/3 pumice and 1/3 lava (the typical APL mix). The results were not spectacular. Some of this was certainly due to my inexperience. However, as an engineer, I am trained to study and use empirical evidence to make decisions. Over three repotting seasons, I noticed that the root structure in my APL mix was not as ramified as the root structure of trees that I bought that had an akadama/pumice mix. So, typical engineer that I am, I spent some time studying the component materials in my bonsai soil mix. I discovered that Akadam is an interesting material in that it is soft enough for roots to grow through, yet hard enough to support the interstitial spaces (small voids) within the soil mix that allow for the quick draining bonsai soils. Pumice is harder but has a significant water absorption similar to akadama. The pumice I use is soft enough to crush with your fingers but it is harder than the akadama and supports/creates the interstitial spaces when the softer akadama breaks down. Lava is the hardest material in the APL mix and will support the interstitial spaces much longer than akadama or pumice but does not provide the higher water retention that pumice and akadama do. In essence, what I have observed is that the lava creates areas where roots simply cannot grow because it is too hard for roots to grow through. Replacing the lava in my soil mix with akadama and pumice generated a soil with more available volume for bonsai roots to grow in. Using the akadama/pumice mix over the past growing seasons, I have had a significant increase in the fine root growth that I had never achieved before. The most stunning example in my collection was an old man Cedar Elm (40+ years old). I had the elm in an APL mix for the first two years I owned it and could never get the root mass (and subsequently the branch structure) to ramify. It was healthy, but never vigorous. In early spring of 2021, I repotted the elm in a 50/50 akadama/pumice mix. This spring we repotted the elm and the change in the core root mass was incredible. The mass had super fine roots and the density was the best I have ever seen in my collection.

    • August Day says:

      So Don, Does you Akadama maintain original form after a year or two or is it like large grained sand after the first year?

      • Don Barker, P.E. says:

        I use different sizes of pumice/akadam for my bonsai. For deciduous trees, it is typically around 1/16″ grains (typically called “small” on a lot of bags from Japan) and thus, I am starting out with what would be considered large grains of sand. For conifers and large deciduous trees, I use 1/8″~1/4″ akadama & pumice. I honestly don’t get that much break down as much as the akadama seems to fuse together (it’s similar to the same affects that was sown in Andrew’s video, pause it around 0:46s and you will see what I mean). It is like the grains stick together. You can still see the individual grains mushed together when I repot (which is about every two to three years depending on drainage and tree development). I think eventually the core mass of my trees will be mostly roots and a fused mass of akadama with pumice grains mixed in. I have seen videos of trees in Japan with their root masses fused together with akadama and it was reported they are like that for decades and still draining well. I have not gotten to that stage with any of my trees yet…

  24. Philip Krieg says:

    Several of us experienced Bonsaists in Southwest Florida tried using Akadama. It turned into a muddy sludge after one normal summer rainy season. We then returned to using lava rock in our mix with pumice and the plants thrived in our hot summer Florida sun. No more Akadama for us…

    • crataegus says:

      Thanks Philip for the observation! Yes, some akadama products break down very fast. Others, very slow. It’s not all the same stuff. Jonas at Bonsai Tonight has written about different akadama brands.

  25. stephen prevost says:

    Lava proportions not mentioned… 1:1:1 or ??

    • crataegus says:

      Andrew was talking about lava percentages of 30% or more being problematic in some cases. This is what I’ve seen too. Take a look at the video if you can, I think we have proportions on there.

    • crataegus says:

      Andrew was speaking of lava in excess of 30% in a mix as being problematic in some cases. So yes, that would include the 1:1:1 ratios.

  26. David Crust says:

    After years of dabbling with exotic ingredients I finally came upon a secret cheapie on-line party favor source that solves all of lifes problems and I have gone to 100% miniature plastic skeletons. Perfect drainage yet good water retention. Spot on PH and easy on the tools. If-un you are creeped out by the hundreds of mini-skulls looking up at you while you dutifully water, why you can top-dress with the dreaded lava crumbles. Life is so good.

  27. Dallas says:

    Thanks for the great article Michael. I have a question about the pumice you mentioned from Idaho. That’s where I get my pumice from. Would you still recommend I use that pumice even though it’s heavy as you said? Maybe mix in some perlite?

    • August Day says:

      I buy pumice and don’t find it heavy, but it was in bags and very dry with no dust.

    • crataegus says:

      Yes it seems ok, a lot like what the Japanese use, closer to that actually, kiryu. Harder and heavier, but still pumice. It likely holds onto less water than Pacific Northwest pumice. But if you have it, use it up.

  28. John S says:

    Watched the video. Read the comments. Lots of variables. It seems focusing on the simple solution, per Occam’s Razor, seemingly one type of rock, leaves many other simple, but harder to fathom reasons, by the wayside. Don’t get me wrong I’m open to actual experimenting. Is it possible we as a cohort of bonsai practitioners are inclined looking for the “Silver Bullet” solution vs digging deeper and looking at what practices led to certain results?
    For example as far as effective root space goes general pumice and lava are both mostly inpenetrable. Adding more Akadama to the mix and leaving out lava (aka Andrew Robson) raises the EFR media (max) from 33% to 50% so the shift basically increases the effective rootspace…. Given 27% to interstitial spaces from somewhere equally below a ratio max of 60% APL to 77% AP. So it’s it likely this akadama shift would be a more likely cause for more and better scaling roots? Something to ponder for sure

  29. Paul says:

    Good information on the lava concerns and the fact that it is high in Boron, but I didn’t see any mentions of the drawbacks of Akadama and being high in metal contents? I’ve heard in mentioned in Ryan’s Podcast near the end of the year when he spoke with David at Apical Ag, and before that I actually had my soil of 1/1/1 tested by Apical in the spring last year and they confirmed the same thing mentioned in the podcast with Ryan, Akadama is high in metal content and dumps it into the soil mix as it breaks down. I believe they mention This side effect causes an imbalance in nutrients that the tree uptakes which then causes the tree to have the inability to produce larger/healthier roots from imbalance. The bonsai community will have you believe that Akadama is a benefit in that it allows for fine root growth from scaling due to the particle structure but in actuality like I mentioned it’s due to improper nutrient balancing and not being completely healthy. So although the trees can produce roots and look healthy they are not getting a proper balance of nutrients to be completely healthy.

    I personally have poor water with higher salt contents after I moved, and me using the same salt based fertilizer was having salt issues, that then were made worse from the akadama breaking down and dumping high levels of metal into the soil and unfortunately killed some off before I learned what the issue was. After treating the trees to balance them nutrients they completely turned around and trees that stalled for months began to grow. I then switched to rain water ans saw even more improvement. Personally as I’m repotting this year I’m doing away with akadama. Based on this conversation on lava, I may reduce that to more heavy pumice with the fir bark I’ve been replacing akadama with.

    • August Day says:

      Good reply! thanks for the info.

    • crataegus says:

      Another excellent topic! Of course there are several reasons to want to walk away from akadama. I’ve some experiments with 100% pumice that are intriguing, with longer roots and in general more vigorous roots. But without the fine roots. That’s been something I’m noticing. Over time I wouldn’t be surprised if in the core the roots become fine, after the mass colonized by these strong roots. But it is a distinctly different root mass than with akadama. Fertilizing so far is about the same as with the addition of akadama. I’ll do another post about that. But your comment about the discussion on the podcast is very interesting. That I don’t have anything to add to at this point.

  30. <

    div>Interesting topic, Michael…but I’m more confused than ever. You and Andrew “avoid” using lava rock, David Degroot reports it limits root growth and you wrote Ryan Ne

  31. Frank Stockmal says:

    Very interesting!! It’s discussion like this that leads us all to take a step back and really question our soil mixes. I personally would like to see more study being done on alternative bonsai soils like diatomaceous earth. Just the availability of this stuff makes me think why am I buying Akadama if this stuff works so well for many who use it instead of Akadama! Why isn’t there more discussion about zeolite?… If we can figure out how to ship Akadama all the way from Japan I’m sure we can do the same with zeolite… and it’s mined right here in Oregon and Idaho!!! I definitely believe pumice is here to stay because it has few drawbacks unlike Akadama. From what I’m hearing from Michael M. and his extensive experience with lava, who am I but not to believe him. Now that we’re finally done with Turface lets add lava to the list….and finally find an viable alternative for Akadama and one that we don’t have to ship it thousands of miles to get it here. They use the stuff in Japan because that’s what they have there and that’s fine for them, and maybe not so good for us like we’ve all been lead to believe.

    • August Day says:

      So Frank, I am unaware of what Zeolite even is. Could you help me there? Also, I live in NE Oregon. Where are they mining that product now if ok to ask, and why is someone not getting it on the market? Thanks, August

      • Frank A Stockmal says:

        The stuff is by Ida-Ore Zeolite mines, its Clinoptilolite Zeolite from a deposit along the Idaho and Oregon border called the Sheaville deposit. It’s very very close to the stuff they are using up in Canada. I think it’s called Chabazite in Canada. The data analysis on this stuff is almost identical to “Chabazite” I’ll see if I can post it here soon. The price is very reasonable compared to Akadama. I talked with the folks at Ida-Ore Zeolite and they will sell it to you but the minimum amount you would have to purchase was a full pallet and had to be shipped freight.

      • August says:

        Ok. I’d like to see what it looks like and know what the water retention facts are with it. I thought I heard some negatives about it awhile back, but not sure.

      • Frank A Stockmal says:

        You can learn more about the Chabazite Zeolite at: :
        I don’t believe they sell into the US though. I runs about $1.05 per pound @ 50 LB bag. So why is it that we here in the US, can’t get this stuff???

    • crataegus says:

      Hi Frank, thanks for the comment—- and I’m laughing! I don’t want people to take my word for it, that some sources of lava may be problematic, but rather to urge people to test their lava. Especially if they see what Andrew is showing in the video, soil just falling away after years in the pot. I’ve seen this too. I’ve also seen nice solid root masses with lava. What’s going on there is beyond the scope of this post. It may be boron, it may be something entirely different. But pure empiricism can’t be tossed because it makes people uncomfortable. It’s only a starting point.

  32. alexbraunton says:

    Hi Michael,

    I thought this was a really interesting article and something I’d never considered or heard before.

    When you quote Andrew, he says;

    “If you take your bonsai out of the pot after many years and all the soil falls away, or you cut the circling roots and all the soil falls away, it’s probably not a soil mix that is working.”

    Could you explain what he means by this please?

    Thank you,

    • Andrew says:

      Hey Alex,

      The roots I’m looking for when I repot are as many dense, fine roots as possible. In my experience, a densely ramified root system tends to help create densely ramified branches. Branches and roots mirror each other. The more fine roots we have, as opposed to fewer thick coarse roots, the more refined and healthier our bonsai tend to be.

      So when I repot a bonsai, and pull it out of the pot, I want that soil mass completely held together by as many fine roots as possible. Because in my experience lava doesn’t create that fine root structure, almost every tree in lava I’ve repotted has most of the soil fall away from the root mass when it’s taken out of the pot or when the circling roots on the outside are cut off. All of this because high percentages of lava aren’t creating dense fine roots.

      • August Day says:

        So what do you mean by “HIGH PERCENTAGES” of lava if I can ask, what % of lava would you call safe and ok.

  33. Dalton says:

    I usually just use the regular store bought red lava as a tiny drainage layer for my bigger pots when training them. And then just use pumice, turface, and then a little bit of mulch soil to keep some moisture throughout the day as it gets pretty hot here in Texas.

  34. Roger Case says:

    Some information
    1. the boron toxicity issue referred to was the result of Iseli Nursery obtaining their lava from a single source, and subsequently noticed root issues, according to Joe Harris at Iseli. They had the lava tested and it had a toxic level of boron in it — subsequently they went to another lava source and this issue hasn’t reoccurred. issues. The lava that I and others in the Portland area use has been screened and collected from the “little nash crater” in southern oregon — it has been tested and has no boron or other toxicity issues.
    2. I never remember Ryan having a lava toxicity issue during the 7 years of classes with him – and just last night he told us by email that he uses continues to employ lava in his soil mix.
    3. David Degroot also has indicated he does NOT use lava but the reason he gave me was lava’s weight and tool impact issue, not any horticultural problems.

    Also, can someone enlighten me as to why some people use 2% lava in their soil mix ?? What is its function at that low percentage.

    • crataegus says:

      Hi Roger,
      Thanks for the notes!
      I’ve been in conversation with Joe as well, and he did have high levels of boron in mixes where poor root growth was witnessed.
      I also had a conversation with Dave DeGroot where he confirmed lab results of “toxic levels” of boron in lava where he’d found poor root growth.
      And yes, as I state in the revisited post, some sources of lava appear to be OK. It’s that some sources do not that concerns me and is worthy of a conversation and more testing. Much of the observations of Andrew come from Texas and the Midwest.
      2% lava is used in the popular Aoki blend, and I too would be curious to know the reasoning. I’ve heard the minerality of lava benefits conifers, but that is just a ‘heard’ thing. I have no support for that idea. Akadama has a lot of minerality too.

      • treetroll1 says:

        Do you think the toxicity issue would ever arise when a tree is planted on a volcanic scoria rock/stone?

      • crataegus says:

        I suppose it could. We have very little data yet that points to some sources having high levels of boron. But because the lava we use are simply small pieces of the same stuff, I guess it could.

      • treetroll1 says:

        It seems to me if there is an issue with boron somehow leaching out of kava used in bonsai mix then the same issue might arise depending upon the source of the volcanic rock a tree is planted.

        now that being said there is certainly
        Much more surface area from which boron and other undesired contaminants could leach in soil scoria than from a rock on which a tree is planted and I do not know anyone who is testing planting rocks for toxic components prior to their use

    • August Day says:

      Good and interesting reply. Thanks for the info!

  35. Geoffrey Holmes says:

    I have been using pumice for quite awhile after buying it at Agway as Dry Stall. It was on the smaller size 1/4” particle. Sadly they don’t sell it anymore. I bought some from Hess and it is whiter. I do find it starts to break down with our New England freeze thaw cycles. I am off the Akadama train too. It breaks down too quickly here. What would you recommend to replace Akadama? I am thinking of using chopped spagnum instead and going back to some fir bark in the mix.

    • crataegus says:

      I’m not sure there’s a replacement for it, because it does some unique things like fine root growth. I’ve been experimenting with 100% pumice, and while the root growth is rampant, it is also leggier than with some akadama. Akadama comes in many hardnesses, though, and if you haven’t yet try some of the harder akadama. Many parts of Japan are like Colorado and freeze all the time, and they still use it—-broken down akadama grows fine roots. So some breaking down isn’t the danger that it is with, for instance, bark. Once that breaks down root growth is limited. Otherwise bark isn’t the worst thing, just needs replacing now and then so I’d keep it to the outside of your root ball.

  36. Tortuga says:


    I think pumice and lava are the best bonsai media any bonsai practitioner/hobbist should use. The results are huge, just try and experiment with one of your trees.


    • Tortuga says:

      I am sorry about my mistake, I meant to say pumice and akadama.

      Cheers guys!

      • August Day says:

        Could someone suggest a place to buy Akadama at a reasonable price or is that impossible, Thanks

  37. Victor Taboada says:

    Important: Michael, what is the difference between Hyuga and Kiryu? Which one would you use in your Akadama/Pumice mix as a replacement for Pumice?

    • crataegus says:

      They are related… Kiryu is translated as ‘river sand’, though that is deceiving. It’s a volcanic rock, essentially a hard pumice. Hyuga is also pumice, a softer type. Closer to the Pacific Northwest pumice. Hyuga will likely create stronger root growth, more aeration. Kiryu is the popular choice of pumice for bonsai pots, Suzuki and others use it.

  38. Wes says:

    I’ve been growing trees in a one-third mix (1/3 lava, 1/3 akadama, 1/3 hess pumice) for the past 8 years. This year, Andrew and I repotted 14 trees, with about half of them in this lava mix and half of them in approximately 50/50 akadama and oregon pumice. There was absolutely no question the root balls were denser with finer root growth on the trees without lava. The trees in lava mix had roots circling the outside of the rootball, but the core would just fall away. We also noted a massive difference in the black pine needles – the needles on trees planted in the lava mix were softer, thinner and lighter in color. The pines planted in the 50/50 mix were thick, a much darker green and painfully sharp. Obviously this is purely anecdotal, but very exciting for my collection to find a solution that we believe will produce much healthier, vigorous trees. Thanks for the post guys!f

    • crataegus says:

      Thanks Wes for the comment!
      Given that we have multiple spots in the country now where lava is implicated in poor root growth, Texas, Washington and Oregon, questions of source arise. It’d be interesting to know what the original source of problematic lava is, what mine it’s from. And whether that mine is supplying many states with lava.

      Even if we can’t get lab data to explain what’s going on in our bonsai pots—-it may not be boron, maybe something else—-identifying which sources are suspect may help others prevent similar problems.

      Not to give you work, Wes! Just a thought for anyone experiencing less than wonderful root growth with a component of lava.
      Thanks again!

    • John S says:

      Hey Wes.

      Thanks for that information.

      Regretfully I’m now really confused.
      So is this observation saying more Akadama was the key? …thus increasing the effective root space.

      Or were these all deciduous and were using Boon 2:1:1 APL. Compared to 1:1 AP?

      If coniferous them I’m left with adding more akadama more pumice and taking out lava is the key…identifying lava as the culprit …and the extra akadama which added effective root space to the rhizosphere is not a factor…which somehow seems to be a perplexing leap in logic. .

      Love to see the trial data to this. It would close the loop and come closer to seal the deal.


    • August Day says:

      If I can ask, what size akadama are you using and is it the “hard” akadama? Also, with the AP mix, what size is the pumice? Thanks

  39. Lee Leikam says:

    Do you know if the lava rock has been sifted and/or washed to remove all the super fine dust? I’ve made a practice of washing pumice due to some being full of very fine ‘dust’ and I’ve done the same for the lava rock. I’m not sure but I feel the dust can suffocate root development. What do you think?

    • August Day says:

      I just ordered a HD 1/8″ woven screen, 3′ X 3′ that I will build a frame around for just that problem. I will wash the fines, the dust and anything else that will go through the screen out of all mixes. If your mix is wet. It is almost impossible to screen out dust. It just sticks to the larger particles and stays with the mix.

  40. Zack Clayton says:

    Two things.
    1. I would be interested in an experiment that soaks the lava prior to use – for maybe a year to see if that would impact the boron/other levels of the toxic constituents. I have a couple of open bins of lava that get regular rain and then drain out at the bottom. I use up to about 25% of that in some of my mixes.
    2. I use turface extensively in all my mixes and it seems the ionic exchange is very similar to akadama that I have tried. it makes sense, it is kiln fired instead of lava fired so the product is very consistent. I wrote an article for our newsletter in the late 1990s with pictures showing rooted maple cuttings in a 2/3 turface 1/3 coffee grounds mix. The fine roots and root density after a year looked like the “without lava” root mass in Andrew’s video clip. I’m retired now and unfortunatly don’t have easy access to that volume of coffee from a work coffee club.

  41. Bruce Winter says:

    Interesting. Everyone here (Hawai’i) uses lava, it’s just too easy. But I did order pumice and used it straight for many years. The root growth was, as you say, “rampant.” If anything, too rampant, so I began to use a pumice/lava mix. Now I’m back to using just lava, for economic reasons. The problem with this lava is that, being jagged, it locks to itself, thereby reducing aeration.

  42. Brett .Summers says:

    I stopped using lava some years ago, we call it scorio, as I noticed I wasn’t getting great results with it. I have tried so many different substrates out of necessity and find most very usable but this stuff I started avoiding. I’m in NSW Australia and used a red variety. I hear they get good results with a black variety in Victoria Australia.

  43. Don Erickson says:

    Thank you and the other practitioners in the PNW for keeping us informed as to the best practices for our little trees‼️👍

  44. Lucas says:

    Michael Hagedorn I read you fantastic book, thank you.

    I had a question due to wanting to move more to pumice without lava, due to expense and availability.

    What are your ratios of Pines vs Deciduous. (Can’t seem to see them on blog)

    And do you lump larches in the Deciduous camp.

    Thanks so much for your time and help.

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