There are lots off different soil types different mixes all used for bonsai and allot of them have proven to be good to grow bonsai tree’s in!
however picking the right soil for your own preferences requires a little basic understanding of what the soil needs to do and why that is so important, only after that you can choose or create a soil mix that suits your needs and as with allot of other things with bonsai your climate and the ability to care for your trees are things to take in consideration in picking your perfect soil mix.
There are lots of different opinions about what soil to use so but they all have in common that as long as you can provide care needed and are aware of the basic’s how soil and how the tree’s work in general and use a pot with drainage holes you are off to a good start!
Key functions of soil
Special bonsai soil is nothing more then a mix of different components that together create a healthy environment for your tree’s to grow their roots in.
some key functions of a good soil are:
Holding water
The roots need water to provide for the tree so the soil needs to absorb water and release it to the roots on demand
Holding nutrients
To help the tree grow the tree get’s fertilized so the soil has to be able to bind and share the nutrients
otherwise each watering the fertilizer will simply flush out of the pot
if you have done some research about nutrients and soil you often come across the word : CEC
this stands for Cation exchange capacity this indicates how good the soil binds nutrients and the ability to return it to the roots.
provide drainage of excess water
Because a bonsai lives in a pot its important that after watering or when it rains and the soil is completely saturated the excess water drains out of the pot, Roots need oxygen to grow and if they stay submerged in water for an extended period of time they might suffocate die and rot away leading mostly to dead tree’s.
so remember that even with a draining soil make sure your pot has plenty drainage holes !
provide oxygen to the roots
It is important to have a open structure soil mix so it is well draining and provides oxygen for the roots.
offer stability to the tree
Because our bonsai live in small pots we need to make sure they are stable in the pots to prevent unnecessary damage to the roots by wind or when working on the tree.
What to consider when choosing soil?
as mentioned before its depended of different preferences and also because of the care that one is able to give their tree’s.
You could divide soil components in organic and inorganic
some soils will hold more moisture or break down over time and require less frequent watering then others while others are more free draining and dry out quicker.
for example, some people will be able to water their trees twice or maybe even three times a day during summer while others are only able to water in the morning/evening due to work or other things in life that require our attention.
there are some advantages and disadvantages with organic or inorganic soils mixes
The advantages to a highly inorganic soil mix for me is that you can fertilize well and don’t have to worry about overwatering your tree’s as much or if you have allot of rain in fall and winter you rarely have to provide extra shelter.
The disadvantages to highly inorganic soils is that during summer and its really hot you often have to water twice a day or maybe provide some shade on the pots during the hottest times of day.
The advantages of highly organic soils are that they hold more moisture and require less frequent watering
The disadvantages with highly organic soils that during periods with allot of rain they can hold to much water over long periods of rain and suffocate the roots.
There are allot of different types of soil components that get mixed up at different ratios to get a good bonsai mix that suit your needs but the most important thing remains that we provide the right care for the trees so provide water or shelter when that is required.
Commonly used soil components
Akadama:
Akadama is a natural volcanic mineral Surface-mined in Japan.
it holds water and binds nutrients very well and is granular based so it helps providing drainage.
frost and thaw cycles can let break down the akadama faster so its recomended to use the hard quality.
its usually applied as base ingredient of a mix together with Pumice or other components.
Kanuma:
Kanuma is a granular Japanese Potting Medium for Acid Loving Bonsai.
This material comes from the Kanuma Area of Japan.
it holds water and binds nutrients very well and is granular based so it helps providing drainage
It’s PH varies from 5.2 to 5.5.
it is light and porous and if used pure its quickly compressed so avoid putting pressure on the soil.
It is more acidic than Akadama, and therefore, used mainly for Azaleas, Camellias, Gardenias, and other acid-loving Bonsai.
Kiryu
Kiryu soil is a type of soil like kanuma especially for acid-loving species such as azaleas, It is a soil extracted from the Kiryu region of Japan, it is a volcanic soil mainly composed of volcanic ash, pumice and peat moss. Like Kanuma soil, it has a very low pH of around 4-5
however Kiryu has a more dence structure and holds less water then Kanuma so is more suitable for trees that require less water then others.
Pumice/bims
Pumice or bims is a type of volcanic rock. It is porous and light structure it holds some water but not as much as other components like akadama.
Pumice is pH neutral and will not decay over time.
When used in a bonsai soil mix, pumice helps to prevent soil compaction and provides support for the roots.
It is often combined with other materials like akadama, , to create a well-draining, growing medium.
because it wont break down its reusable after sifting it.
Moler clay/terramol/diatomaceous earth
Moler clay/terramol/diatomaceous earth is a natural product containing diatoms(tiny alagea fossil skelletons) and clay that is mined in Denmark.
It is ph neutral and holds allot of water and nutrients its granular shaped and will not break down over time this makes it an ideal base soil component and is often mixed with pumice and other components.
because it wont break down it is reusable after sifting it.
yes i know it is sold often as cat litter but allot of people use it successfully to grow their bonsai.
Perlite
Perlite is a lightweight granular material that’s white in colour. It looks and feels like little bits of polystyrene but is actually made from expanded volcanic glass, heated to 1000°C until it ‘pops’ (like popcorn) to many times its original size. It’s lightweight, sterile, and easy to handle, and is long-lasting. It’s ph neutral
Perlite’s expanded nature makes it extremely porous, so it can absorb water, but it also improves drainage, so is ideal to mix into compost to ensure water drains freely. Perlite is particularly useful in plant propagation, including taking cuttings and sowing seeds.
Zeolite
Zeolite is a mineral granular based that holds allot of water and helps keeping a open structure to help with drainage.
another great benefit of zeolite is the high CEC capability
zeolite is often used as an addition to a base mix.
be aware compared to other soil parts its pretty heavy so when added to big pots it increases the total weight of the pot.
Pine bark
Pine bark is a organic material collected and crushed or shredded and then used as growing medium for plants.
as it has a chunky structure and holds moisture it will break down over time releasing beneficial organic material in the pot but the breaking down process is slow so it will not effect the drainage of your pot in a negative way.
its often mixed as an addition to main components like Moler clay
Coco coir/peat
Coco coir organic fibers extracted from the outer husk of a coconut.
it retains allot of water and does not break down allot over time providing stability and drainage in the pot.
its usually mixed in as an addition to main components like Moler clay or other base ingredients.
My own experience
Over the years i have successfully used allot of different components and managed to keep tree’s happy.
What works really well for me and my trees is a mix of 1/3 Moler clay 1/3 pumice 1/3 Pinebark
but also i have trees in Akadama mixed with pumice that are doing very well and even some trees stay in their nursery soil for a couple years before repotting.
as long as you understand how it works and you adjust your watering to the needs of the soil or protect the pots from heavy rain if needed you can come a long way keeping trees alive in allot of different types of soil in combination with a pot that is able to provide plenty of drainage!