Secrets in the soil – calling all Albertans!

I’ve been wanting to write something about bonsai soils for quite some time now. After dancing around the subject for about two or three months throughout our long winter here in bone chilling and dry Alberta, I decided to face my fears and come out digging deep…haha punny. See what I did there?

The intention of this post is to tell you about my soil plans for this year. It is by no means a guide. If you are looking to obtain advice by reading this the only advice I want you to carry with you is that it is you that must decide how to create your optimal soil mixture for your trees. If you are looking for good basic advice on soil, I highly recommend Randy Clark’s article “Guidlines For Creating Bonsai Soil”, from the Bonsai Learning Centre. He describes in really great detail the essentials of what you should know when choosing soils for the first time.

I’ve looked all over the internet, books, talked to people in the profession and have basically decided that in order to know what my soil should consist of, I must consider several things. What is available to me, what are the demands of the growing conditions in my region, what type of pot am I using and finally, what are the demands of the plant itself. Some trees prefer higher moisture levels, alkaline conditions, varying organic/inorganic ratios while others don’t. All of these factors will dictate what your soil will consist of.

Initially, I think what I am going to do is choose soil based on species type, i.e. deciduous vs. coniferous. From here, I will consider the demands of the environment and the type of pot I am using. Generally rock material you find at your local landscaping company works best in your area. For instance, typically we have really dry springs with continued freeze thaw which is damaging to the trees and our roads… Then we will have a hot summer with variable moisture, usually in the form of flash flooding and hail, which is damaging to the trees. Then we will either have a dry fall or a fall with a substantial amount of precipitation, either of the which lead into a dry and cold winter. In this instance, the landscaping company in my area has a variety of rock that you can choose from. Lava rock, shale, river rock, rainbow rock, bark, etc.

Regardless of your climate the most important factors you must allow for are optimal drainage and aeration as well as pH homeostasis throughout your soil adequate for your trees needs. For my trees I am going to use a loose, well draining soil mixture consisting of lava rock, red shale, pumice, charcoal and pine bark. I’m still deciding whether or not I actually want to you use pumice, it is not very aesthetically pleasing.

Given my background in science and access I have to many resources, I had the opportunity to do a microscopic analysis of each.

Lava rock is pretty common here and can either be found as red, black or gold. For my purposes, I am going to use the red or gold since black would absorb to much heat and eventually end up killing my trees. Lava rock is really great for holding moisture because of it’s high porosity shown here:

lava1 lava2

Red shale or “Turface” is the red rock that can be found at baseball diamonds. In my case to avoid being arrested, i’ll just purchase mine. The benefit of red shale is it rigidity, which helps the development of feeder roots. Feeder roots as you know, coincide with your current growing season. Dense feeder roots = strong growth. My apologies I did not take photos for this, i’m having a hard time finding the right size of shale. After checking many landscaping places I still have yet to find something that isn’t huge or fine dust.

This is an electron micrograph image of turface also known as haydite which is a derivative of Turface. Notice that it too is porous and rigid.

Pumice, like lava rock is also very porous. My reasoning for using pumice is that it will also hold the moisture levels in the soil.


The bubbles in pumice are more dense and smaller than that of lava rock, yielding higher absorption and will retain your water and fertilizer.


Charcoal will aid in maintaining an neutral soil pH 6.5 – 7.5 where applicable. I’m only going to use a small amount per pot since a little goes a long way. Per litre, I will use ~ 1 – 2 tablespoons. For those of you outside of Canada scratching your heads thats 0.22 gallons and 0.01 – 0.03 quarts (US). I won’t include an image of this since I’m using it for chemical purposes rather than for it’s physical properties.

Finally, for my organic soil component I am going to use pine bark or the bark of hemlock fir. They both are readily available and will slowly and effectively release nutrients essential for optimal growth.


As you can see in both images, various crystalline structures exist on the surface and no doubt through this piece of pine bark. These most likely represent the essential minerals needed for the tree to sustain it’s development.


For deciduous, I will add Lava rock : Red Shale : Pumice : Charcoal : Bark in a 20:20:20:5:35 ratio.

For conifers I will add those same soils in a 25:25:25:5:20 ratio.

After I’ve mixed it this is what it looks like.


You are probably wondering what that lighter brown stuff is, I snuck some akadama in this batch to see how it will fair out. I’ve heard both good and bad things regarding this aggregate and figured since I have it I would throw some in. This soil size is good for both Shohin and Kifu size trees.

I’m still on the hunt for some of these materials as these components where gifted to me from Vriend’s bonsai. Lava rock has proved to be readily available everywhere in many different colors but finding the right size has been difficult. I may have to crush it down. Shale is also available everywhere but in the wrong sizes and I am considering substituting for Alberta Rainbow rock or some sort of washed rock. Burnco supplies a lot of products that would work for me.

Here are some other great posts about what others have used:

Peter Tea Bonsai

Adam’s Art and Bonsai Blog

Crataegus Bonsai



Columbus Bonsai Society


17 thoughts on “Secrets in the soil – calling all Albertans!

  1. Thanks for the really informative post. It’s interesting how porous the material is. I guess in a small container, drainage is by far the most important consideration.

      • I know that bonsais need constant fertilizing. Is it because the soil is so porous? I wish there was a way to balance the two, providing good drainage and nutrient retention.

      • They most certainly do need feeding. Not because the soil is porous but rather because it is 3/4 inorganic components (in my case anyway). The mulch that I add to the soil will provide essential nutrients throughout the year but I still fertilize during the growing season. There are many many ways to do this which you can find on blogs like Peter Tea.

  2. Great post on the always debatable topic of bonsai soil. Lol. I am actually in the process of writing a post on my available soil ingredients and watering as well. I will make certain to link your post with mine :).

  3. Hi Jamie,

    Good post. Thanks for sharing your experience with Alberta Bonsai. There is not a lot of information out there and its nice to see.

    By the sound of it your potting mix is similar to “Boon’s Mix” – which I’ve been using for a few years now – but you use bark instead of Akadama. Question for you: have you found sources for your aggregate of a suitable size (1.58mm – 6.35mm), specifically, sources of lava rock, pumice and fir/hemlock bark?

    I live in Calgary and I have not been able to locate these constituents here. I have resorted to pulverizing rock (hammer) and chopping wood (in a food processor and coffee grinder – oh the pain!). It’s a slow and messy process; I don’t recommend it and I would like to find a better solution.

    I also wanted to also ask you about your preference for bark over Akadama. The problem with Akadama is it’s inability to withstand the freeze/thaw cycles in Alberta, that, and the cost and lack of availability. I grow mostly sub-tropicals indoors (I live in an apartment) along with a couple of JMs that I maintain in a miniature greenhouse and overwinter in an insulated garage. Akadama has proven to work fairly well under these conditions – I can get about 3 seasons out of a Medium-firm grade before it collapses.

    I suppose the issue with using bark are the tanins and the lack nutrient availability in un-composted sources. Have you found composted sources? If so, where/what is it called?



    • Thanks for your response! There is a lot of information out there about soil mixes, the only thing is that the bulk of it is tailored to the individuals geographical location. Unfortunately like yourself, I have not found a suitable size of lava rock in particular. I’ve resorted to purchasing the large bags of crush from home depot and smashing it to bits with a garden wall stone over a concrete slab. The weight of the stone is enough that I don’t have to put a lot of momentum to crushing it. Just be careful not to absorb the shock or you could really screw up your wrists. It is messy and time consuming but kind of rewarding in the end….but messy. Don’t forget to wear a mask, you don’t want that stuff getting in your lungs.

      As for the bark, i’ve found the best source to be the bags you can purchase at the pet shop for reptiles. It is of small enough consistency that works well for your soil. You are right when you mention about Akadama and since I’ve written this post I have learned that this is not a suitable additive in soil in Alberta. I no longer use it in my soil. What I use now is Lava rock, pumice, bark and alberta pebble. There is a new soil aggregate i’d be interested in trying called upsalite. See article:

      The lack of nutrients in bark is okay as long as you are fertilizing. I wouldn’t recommend the use of compost since it contains harmful bacteria that will most likely doom the life of the tree by causing root rot and all other sorts of nasty problems.

      My best recommendations is to pay attention to what others are doing like myself, find and join a local club and look in places like landscaping companies.

      Thanks for reading!

  4. Finding Pumice of a suitable grade – of any grade for that matter – has been very challenging. I have resorted to breaking larger chunks (1.5″) down with a sledgehammer but the results are not very satisfactory. There is a great deal of waste (>30%) and the process is tedious. My pumice source was quite expensive but since they went out of business the only other source is more expensive still. If I ever find a source I will let you know. Please return the favour should you as well.

    At present I am trying out an aquarium substrate, CaribSea Flora-Max, as a source of lava rock. The the average size is 1/8″ with very little waste (<5%). The one drawback is the additional laterite in the mix of which makes up approximately 50%. As a result I am not using any additional fired clay in my mix. I say that laterite is a 'drawback' because I would prefer to have control of what ends up in my mix.

    The issues with Akadama – unless you can get the "hard" grade, which I have never seen – are relatively minimal with indoor growing but a serious problem for outdoor growth.

    The issues with bark in bonsai are discussed here: Although I would like to see some numbers around some of the claims in this piece, the author is usually not prone to superstition. They also emphasize the need for composted bark in the mix to minimize acid and nitrogen leeching. Your concerns around bacterial and fungal pathogens seems reasonable and requires further investigation.

    There are no active bonsai clubs in Calgary. A city of over 1 million people and no club…it boggles the mind. As for sources of aggregate: I have tried every landscape company in town. Orchid growers. Aquarium supply shops. Liveries. I open to any other suggestions you may have.



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  7. Awesome Post. I am from Edmonton here as well, and have been driving all over the place trying to come up with a suitable soil mix, seen you have found lava rock at home depot? where else have you found some of the materials you use for your mix? i am very new to this so all of this becomes almost daunting reading over 100’s of forum posts.

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