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:
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: