You will agree with me when I say that a good soil mixture is very important for a Bonsai to thrive.
But you might wonder what makes a Bonsai soil mixture good! Well, you’ve come to the right place, here you’ll learn everything you need to know to make the best soil mixture for your Bonsai plant from scratch.
I’ve learned that, while improper watering of a Bonsai plant is a major cause of Bonsai deaths (learn how to water properly here), the correct soil is a much bigger contributing factor than people realize.
Over the years, our team has done a lot of research about the best type of soil for Bonsai plants for the Indian Climate, and found that some of them work much better than others. I will tell you that recipe down here, so keep reading.
So let’s get started with a quick background on Bonsai.
What is a Bonsai?
The work Bonsai simply means “a plant in a tray“.
Bonsai is an art that has evolved by taking nature in its rawest form into inspiration. Many styles of bonsai have emerged over time and it a Bonsai artist’s imagination is the limit to his creativity. There’s no doubt that bonsai has its roots from Japan, but it has become a lot more popular in our country lately.
Every day we see tons of people falling in love with Bonsai Plants and its unique art forms.
If you are a beginner in Bonsai and looking for a comprehensive guide, check out my post on ‘Bonsai for Beginners‘.
Hey before we go further, it would be awesome if you could support us by visiting our exclusive bonsai nursery You, Me and Bonsai in Saket, Secunderabad. We have a collection of over 300+ species and styles of Bonsai. It would be a great place for you to start your Bonsai Journey. We also take Beginners classes for Bonsai enthusiasts. Follow us on Facebook to stay in touch!
Table of Contents:
- Criteria for ‘Good’ Bonsai Soil Mixture
- Can I use regular garden Soil?
- Basic Ingredients of Bonsai Soil
- Our Soil Mix recipe
So let’s get started with, what makes a good Bonsai soil?
Criteria for ‘Good’ Bonsai Soil Mixture
Good Water Retention
The best soil for Bonsai in pots will hold enough water for them to absorb what they need, but still dries out quickly so the roots won’t rot.
Excess water must be able to drain immediately from the bonsai pot. Soils lacking good drainage are too water-intensive, lack aeration, and promote a buildup of salts.
Excessive water in the soil may also cause the plant’s roots to rot, leading to a weakening and the possible death of your Bonsai Plant.
Want to learn more about bonsai pots? Check out our comprehensive article about ‘Choosing the right Bonsai pot for your plant‘ here.
The particles used in your bonsai soil mix should be of sufficient size to allow tiny gaps or air pockets between each particle.
As water drains through the soil it pulls oxygen down to the roots (not commonly known is the fact that plants absorb a great deal of oxygen through their roots).
Aside from the roots’ need to “breathe” oxygen in the soil promotes the development of “good” bacteria and mycorrhizal (symbiotic associations that forms between plant roots and fungi in a bi-directional movement of nutrients where carbon flows to the fungi and inorganic nutrients move to the plant) so the processing of nutrients can start even before they are absorbed by the plant’s roots.
The soil must itself contribute only limited nutrients to the plant, to allow the bonsai artist to control the application (when, quantity, and type) of nutrients that the tree will receive.
Therefore, the gist is a soil works fine as long as it provides excellent aeration and drainage.
Can I use regular garden Soil?
Well, for starters, BONSAI DO NOT GROW WELL IN SOIL.
It may sound like a bold statement and it’s a statement for discussion. As per the above section, where you learned about the essentials of a soil mixture, the garden soil doesn’t provide any of them.
A pot of regular garden soil will hold far too much water for too long than the tree requires it. On top of this wet soil becomes very compacted very quickly, so we end up with two conditions in the pot which prevents oxygen getting to the roots and root-rot quickly occurs.
Basic Ingredients of any Bonsai soil
I always tell people that the right recipe for bonsai soil is like the right recipe for a perfect lemonade. Everyone has a slightly different idea of what should go into it, but the basic ingredients generally remain the same.
Before we get into the ingredients, let’s learn some basics that govern choosing those materials.
1. Soil pH
Soil pH is a measure of the acidity or alkalinity of the soil on a scale of 0 to 14. Neutral is 7, while less than 7 is acidic, greater than 7 is alkali. This is our basic 7th grade science and understanding this is key to your bonsai health.
Soil pH affects the amount of nutrients soluble in soil, water and, therefore, the amount of nutrients available to plants. Some nutrients are more available under acid conditions while others are more available under alkaline conditions.
What should the pH value of your Bonsai soil mix be?
It should be essentially pH neutral… that is, neither wildly acidic nor basic. A pH value somewhere in the 6.5 to 7.5 range seems best. Some people also recommend the pH of the soil mix must be like the plants native soil.
Most deciduous trees (e.g. maples, elms) prefer soil that is nearly neutral— 6.5 pH. But conifers prefer a slightly more acidic soil, around 5.5 pH.
Organic mixture or inorganic mixture?
As far as I’m aware, there is no physical advantage in using any organic matter in your bonsai soil, but there are some disadvantages.
- After a time organic matter will break down into fine particles and, if mixed with other more stable ingredients, it will wash down to the base of the pot to form a pan that inhibits drainage
- Once bone dry, most organic matter actually repels water and is difficult to re-wet.
We can grow plants of all sorts in a totally inorganic medium, but they require major and minor nutrient supplements as well as the introduction of all manner of microbes to compensate for the unnatural habitat the roots have to deal with.
So what we propose, is a mixture of both.
Plants will thrive better and be stronger and more independent if it is growing in a soil that provides a natural environment for roots and all the microorganisms that make a soil ‘alive’. To achieve this, a certain amount of organic matter is necessary, but too much organic matter is unnecessary and often counterproductive.
Organic Components of Bonsai Soil:
- Sphagnum Moss
- Lava (Scoria) / Red or Black Soil
- River Sand
Let’s see each of them in detail.
Bark has a fairly high cationic exchange capacity (the ability to absorb nutrients for future release) but it is generally very acidic and it keeps much of the nitrogen to fuel its decomposition, so its usefulness as a soil component is dubious to begin with.
Sphagnum moss is the best rooting medium on the planet – if it is fresh. It is easily available in your local nursery. Dried sphagnum crumbles to dust in next to no time, whereas fresh moss keeps its structural integrity for the duration of its use in a pot. So make sure you wet it before use.
Akadama is entirely unique and can’t be fairly compared to any other mineral, so let’s deal with that first.
Akadama is a naturally occurring clay-like (but not clay) mineral found only in one region in Japan. It is surface mined, dried, graded and packaged. It involves no baking or firing. When wet, it does not form a slurry like clay but forms a gritty paste.
Akadama is with no doubt the absolute best growing medium for Japanese maples and many other broad-leaved species and is arguably one of the best ingredients to incorporate in smaller proportions for most other species.
Some growers complain that Akadama readily breaks down into much smaller particles and therefore impedes drainage, but they are not watching closely enough. Certainly it breaks down, but this only means that the pore spaces become smaller, not that they disappear altogether.
Since Akadama is not a clay, but a kind of cohesive sandy structure, it still drains efficiently after several years in use just as sand would.
But as said earlier it is only available in one part of Japan and very expensive. So this is out of your equation for us.
Lava (Scoria) / Red or Black Soil:
Lava is solidified molten igneous rock that has flowed from volcanic eruptions. It is essentially foamed glass with sharp edges and partially interconnected pores. Depending on its source, most lava contains some heavy metals and potentially some minerals useful to plants.
Roots cannot grow into or through lava particles, but they can and do penetrate the pores to a certain extent. Lava can hold a considerable amount of water (up to two and a half times its weight) but it takes several hours of soaking for the particles to become fully wetted due to the microscopic channels between pores, where channels exist.
As a soil ingredient for bonsai lava performs well. I have seen a very strong root regeneration on newly collected trees planted in almost pure lava. Another major advantage lava has over Akadama is that we can salvage it: after use it can be dried, sifted and re-used time after time.
Like lava, pumice is a product of a volcanic eruption, but there the similarity ends.
Rather than solidified molten rock flow, pumice is the non-crystalline solid form of molten rock that is blasted out of a volcano at extremely high pressure and temperature. It is this rapid decompression that happens as it leaves the volcano that gives pumice its softer texture and more interconnected pore structure.
Pumice can hold large quantities of water – up to four times its own weight. This, coupled with the soft and easily powdered surface means that when used alone or with other absorbent materials, careful watering is necessary to avoid water logging.
Although soft, roots cannot penetrate pumice – even the surface pores since they are far too small. However, since the surface of each particle is soft, roots seem to enjoy their company very much, and ramify well. After a while, the roots seem to break down the surfaces of the particles to form a micro-environment of small particles and dust that keeps them snug and fine.
Pumice drains well but it loses its properties in a couple of years . However, drainage is never impeded to the extent that it becomes a problem.
Turface is calcined montmorillonite clay ( Quite a mouthful isn’t it!). Calcining is the process of heating a substance to a temperature high enough to bring about a ‘phase transition’ – a change in physical state (like baking a cake!).
Turface is heated just enough to stabilize the particles – to prevent them forming a slurry when saturated, but not high enough to reduce its absorbency rate.
Clay Fact: If clay is fired to the highest possible temperature, the result is so hard and non-absorbent that it is used for super sharp knives. Reduce the temperature and we have stoneware; reduce it further and we have oven-proof earthenware, Terra-cotta (as in flower pots). As the firing temperature decreases, the absorbency rate increases.
Popularly known as Grit, or otherwise known as gravel or sand. Grit comprises grains of stone between 1.5mm and 3mm. Anything smaller is sand, anything larger is gravel. We use primarily grit to reduce water retention in the soil in general, to aid rapid drainage after watering, and to maintain an open soil structure. It also adds weight to the soil making it a more stable anchorage for roots.
Now that we have learnt about the ingredients, let’s dive into the good stuff.
Our Bonsai Soil Mix Composition:
As mentioned earlier, each Bonsai artist has their own soil composition and it might have worked wonders for them. The composition you will read below is the one we have been using for the past 30 years for our Bonsai. And if you follow us on our Facebook and Instagram page, you would know that our Bonsai collection is one of the best in India.
What we use?
- Red soil
- River sand
- Yard Manure / Vermicompost
Composition of our Mix:
We use a media(Soil) mixture made of equal parts of red earth, yard manure and river sand.(1:1:1 in ratio). Make sure you divide the parts by volume not weight. For e.g If we take one pot of red earth soil, we take one pot of river sand and yard manure for the mix.
We dry each part and take one part each by volume red earth manure and sand, and we mix them very well. We also add moss on the top which helps us in watering the bonsai.
The moss as explained above is an excellent rooting medium. If you use moss on your bonsai, make sure that the moss does not cover the entire surface of the pot and that you can always inspect the moisture condition of the soil. There is a Japanese rule which says moss may be permitted to touch only three sides of the container. If followed it means that you will always be able to inspect the condition of your soil easily.
The one part of the river sand helps with aeration and the equal parts of red earth and yard manure help the Bonsai with the required nutrition and water retention.
The size of the particles used is important. For example, a mixture made with larger particles will drain faster than a mix made using smaller particles.
A small pot will have less soil and tend to dry out faster than a larger pot. We can keep a small pot from drying out too quickly by using smaller sized soil particles in the mix. The following table shows the size of particles recommend for different size pots.
HOW TO MAKE OUR SOIL MIXTURE ( Step by Step Procedure) :
Take equal parts of Red soil and yard manure with one part of the river sand and then sift each material three times. Here under is a step-by-step process of how you need to do it:
- First, sift using the largest screen and keep the material that doesn’t fall through the screen into one pile or bucket.
- Now use the medium screen and again sift the material that went through the largest screen — keep the material that doesn’t fall through the screen into another pile or bucket.
- Now use the finest screen and sift again — keep the material that doesn’t fall through the screen into a third pile or bucket.
Once you are done with the sifting, then mix all the parts thoroughly and Tada! Your Bonsai soil mix is ready.
Now that your soil mix is ready, pot your Bonsai with it and let us know the results down below in the comments. As said earlier, each of you might have your own recipe of Bonsai Medium/Soil mix. So comment the composition you use for your Bonsai Soil below and tell us why t works well.