Updated: Jan 7
Bonsai Soils, This is a big rabbit hole but lets try and break the basics of this down into a small article and see if we can get a better understanding of what different substrates do and what they should be used for. Most of the time if you ask a Bonsai Professional or someone who is experience what mix you should be using they will ask you more questions then you asked them. And if they dont and they tell you what to use it may not be accurate as well all have different trees, pots, climates and watering conditions.
But lets get stuck into it.
Development Vs Refinement
When learning about Bonsai you will hear a lot of terms when it comes to substrates especially when it comes to professionals. you will hear things like lava rock, pumice, akadama, kanuma, kyru, scoria, zeolite and perlite just to name a few. You will also hear rations such as 1:1:1 or 2:1. This can sometimes be overwhelming but once you understand the basics this will all fall into place. Now all that stuff i mentioned above is for trees in refinement, basically trees that have finished developing and are going into a bonsai pot to start growing the finer details of the design.
Lets start with Development. Development is when we take young material and grow it so we can develop a nice thick trunk and first branching, this is the first part of the Bonsai Journey. To gain rapid growth in the tree not only do we need plenty of unfiltered sunlight, nutrients, good watering and a nice deep pot but we also need the correct growing medium.
When we are developing a tree what we need to do is try and grow thick elongating roots, the top of the tree basically mirrors the root system, so if you grow big thick elongating roots you grow a big thick elongating tree, if you grow fine fibres roots you grow fine detailed branching.
So how do we achieve the thicker elongating roots? the answer to that is a dense organic soil mix. This is basically potting mix. Things like Coarse river sand, pine bark, pete coir and any other type of organic soil will cause this growth. The other thing we need to have with this is a deep growing container. The longer your roots can grow down the more rapid the growth will be. Me personally i use a mix of coarse river sand, fine pine bark and perlite. the perlite is to add a little extra drainage to the mix so that i don't end up with root rot from sitting water.
Now what if we are in refinement and in a Bonsai Pot? this is where the game shifts.
If we were to continue growing in the dense medium we would never be able to get fine ramification and delicate branching in the refinement process as like discuss before we would have thick elongating roots. Once we move into refinement we now need to start growing fine fibres roots to get that effect on our tree.
This is where in organic substrates come into play, once again things like lava rock, pumice, akadama, kanuma, kyru, scoria, zeolite and perlite just to name a few. But there are some things we need to discuss before we choose which mix of these components we need.
here are a few things we need to take into consideration
- Species type
- How much water mobility our tree has ( depends on species type )
- Nutrient retention
- Moisture retention
- Oxygen capacity
- How long we need the tree to be in the pot for
- Your weather conditions
But the 3 main things are Water Retention, Oxygen Capacity and Nutrient Retention.
To figure out the mix you will need to research each substrate and its ability's.
For example, i personally use 100% Akadama with Australian Natives as they take up a lot of water and akadama has great water retention, has nutrient holding capacity and is very well draining. The down side to Akadama is it breaks down quick ( around 18 months ) and when it does this you lose your Oxygen Capacity in the substrate and we need a balance of water and oxygen for a healthy tree. With our australian natives though we are able to repot every 2 years without setting the tree back too much in the refinement process.
On the other hand for Conifers such as junipers and pines i use a mix of Akadama, Pumice and Zeolite. This give me my water retention, nutrient retention, and fine root growth in the akadama, and 2 substrates that wont break down ( pumice and zeolite ) as we need our conifers to be in the Bonsai pot for a lot longer ( around 5 years ). if we were to use just akadama the mix would be well and truly anaerobic by then.
For others these mix's wont be any good as different conditions can also cause a mix to change, for example if you live somewhere very hot during summer and are not around most of the day to water you may consider adding 20% kanuma to your mix as it has excellent water retention, couple that with akadama and youll be on the safer side for watering.
This also goes for windy locations, wind can dry trees out very quickly and if you are not around to water having some extra water retention in your substrate is something to think about.
If you live somewhere that has a lot of rain through out the year you might consider a mix with higher drainage and less water retention.
As you can see this all comes down to researching the different substrates and analysing your conditions and also your species, broadleaved trees move more water then conifers so you would need a little extra water retention. but i hope this article has some what helped. we have only scratched the surface but it is a great start just to shift your mindset when looking at soils.
Until next time enjoy your Bonsai Journey!
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