Soil pH and Bonsai

Ask a room full of Bonsai artists about soil and you will probably get different perspectives from each and every one of them. Soil for Bonsai cultivation is widely discussed and opinions are easy to find. From those who can afford to import Akadama and other Japanese sourced mediums through to Cat litter soils and organic mixes, all serve a purpose. In the end it is probably better to talk about the “Growing Medium” rather than soil as some Bonsai trees grow in mixes that can hardly be classified as Soil when one goes with the “normal” definition of what soil is. Here in New Zealand we just refer to it as “dirt”, but that is probably not good English for what we use to grow our Bonsai in. One thing that is not very well considered when it comes to soil and soil types, is the pH of the soil for Bonsai.

Ph is a measure of the acidity and alkalinity of the soil and is expressed on a scale that goes from 0 to 14. ) is very acidic, 7 is neutral and 14 is very alkaline. Soil pH is largely determined by the type of rock or parent material that the soil originates from. Limestone for instance will produce soil that is more alkaline. Soils with a higher content of decomposing organic material normally lies on the acidic side.

The pH of the soil is important as it affects the control of the solubility of different minerals. Different minerals are available to plant roots at different pH levels. What is available and can dissolve at a low pH, will not be available at a high pH as the solubility of the mineral is effected. Soil pH also has an effect on soil structure and the activity of soil organisms.

Some plants do not have a big issue with pH levels, but others are very specific. In the satsuki-azalea-bonsaiBonsai world, Azaleas and Camellias could be a good example. These plants prefer a slightly acidic soil. Fruit trees also produce more fruit  in slightly acidic soil. This is not a major consideration for Bonsai artists as Fruiting Bonsai are not necessarily grown for its fruit. As a whole, pH is something to be kept in mind for Bonsai artists, especially for those pH specific trees, but our larger concern should be for the drainage capacity of the soil. Here-in lies another challenge. Due to the free-draining characteristics of most Bonsai soils, it is very easy for minerals to dissolve in the water and be washed out of the soil. It is therefore important to fertilize the trees and to ensure that a good mineral supply is available.

What do you water your trees with? Water you say. Yes, but not all water is created equally. Your water supply could contain different types of chemicals that can in turn be deposited in your Bonsai soil and over time, alter the pH of the soil. Areas where the air is highly polluted can acidify the rain water and this in turn can change the chemical composition of your soil. So, what to do?

Common sense and logic, although sometimes scarce, should prevail. Water your plants with what you have available. If it is rain water from an unpolluted source, you are winning Lotto. If it is town sourced, it could contain all sorts of things like fluoride. The main thing is to be aware of your water source and to act accordingly. Also know that regular watering will wash nutrients out, therefore fertilize and use mineral supplements. If you are worried or just inquisitive about the soil pH, get a digital tester or a testing kit and determine the pH. If there is a problem, it can be rectified by either a preventative strategy (like only use unpolluted rain water or do not use organic material in your growing medium) or use supplements that will get your soil to the ideal pH for the specific tree. My experience is that to not let pH become something that makes you lie awake at night, but to use the opportunity to get to know more about your tree, find out about its specific pH preferences and then adjust by either supplying minerals or changing your growing medium when needed.


Images are open source and the last one is from

Mycorrhizal fungus – Root friends


The white threads are Michorrizal fungi.

Mycorrhizal fungi occurs naturally in soil. They form a close symbiotic relationship with plant roots. They are called mycorrhizae ,from the Greek “mukés”, meaning fungus, and “rhiza,” meaning roots. Mycorrhizae are considered to be in a mutualistic relationship because both organisms benefit. The fungus receives the products of photosynthesis from the plant and is therefore does not need to find its own sources of energy. At the same time the fungus grows out into the soil and retrieves nutrients, especially phosphorus and nitrogen, and passes these back to the plant. It is usually seen as a network a very thin, white threads spread throughout the soil in close contact with roots.


The root on the right has the fungus in close contact to enhance the absorptive area of the root. This means more nutrients and water can be absorbed than the root on the left.

However, in most soils that have been disturbed by residential construction, or intensive cropping practices with applications of fertilizers containing pesticides and other chemical products, the mycorrhizae content has considerably diminished, and has become insufficient to significantly enhance plant growth. Numerous experiments have shown that plants without mycorrhizae cannot cope as well with low mineral levels as those that have mycorrhizae.


In a Bonsai pot, the soil is a very controlled environment. The Bonsai artist determines what goes into the soil, what it consists of and how much water is given.

When mycorrhizal fungi colonize the plant’s root system, they create a network that increases the plant’s capacity to absorb more water and nutrients such as phosphorus, copper and zinc. This process in turn enhances growth and favors rapid development of roots and plants. Where this fungus is present in soil, a much faster establishment rate of new roots is observed as well as a reduced water need of up to 30%. The reason for this is that the micorrhizae ensures a much larger surface area is available for the absorption of water and nutrients. The plants are healthier and grow faster.

There is also evidence that these fungi can also improve the structure of the soil. The threads grow through the growing medium and aggregates the soil. This allows for more air to move through the soil as well as enhancing drainage.

Back to Bonsai cultivation. As mentioned before, the soil in a Bonsai pot can be very sterile as it could consist of particles that do not necessarily contain living organisms or lots of organic matter. These could include valuable soil bacteria (nitrogen fixing bacteria) as well as michorrizal fungus. In the absence of these, it is important that the Bonsai artist allows for modsc_1936re (more frequent) fertilization to take place. Michorrizal fungus spores can be bought (I have not seen it in New Zealand yet), but a much less expensive way to inoculate your Bonsai soil with the spores is to use a bit of the original soil in the Bonsai pot at planting time. I find that this is especially important when I plant Pines and other conifers.

In summary: Most plants in nature live in a relationship with Micorrhizal fungi. Both organisms benefit from this relationship. Most Bonsai soils will not contain this fungus and by adding the fungus to Bonsai soil, the plant will establish faster, take up more nutrients and will need less water. Something to think about when it comes to transplanting time.

Nebari – The Root of the Matter


These roots have grown over time, dropping of the side of a cliff.

No, we are not talking about the Nebari fictional alien race from the planet Farscape, but the Japanese term generally used to indicate the roots and specifically the root flare at the bottom of the trunk where the root region starts. It also indicates the visible surface roots.

Wikipedia refers to it as: “Also known as “buttressing”, nebari is the visible spread of roots above the growing medium at the base of a bonsai. Nebari help a bonsai seem grounded and well-anchored and make it look mature, akin to a full-sized tree.”


My idea is to write three or so Blogs focusing on Nebari and the development of roots. There is no doubt in any Bonsai artist’s mind that the roots of a plant is where it all starts. Healthy roots = healthy plant (generally). A plant absorbs most of its water and nutrients from the soil through the roots. We therefore have to know something about soil and its water retention and draining properties. Not all soils are created equally. We also need to know something about the physiology and anatomy of roots. This knowledge will help us to understand many of the concepts around root pruning. This will come in later Blogs.

Autumn bonsai images 2014 (17)

A tree growing in a woodland area. These roots definitely add to the character of the tree and indicate that it has been there for a while.

Getting back to the Nebari, the main aim of establishing a root flair at the base of a tree is to indicate age. A wider base caused by a flaring just above the roots, helps to establish the taper of a tree. One way to develop taper is to increase the circumference of the tree at the base and to keep the top of the tree relatively thin. Young trees do not have a huge flair at the base, but older trees show this without fail. In saying that, there are trees that are used for Bonsai that do not show a big root flare. Junipers come to mind here.


The roots are spread over a flat surface and tied to this surface.

There are multiple methods to improve the Nebari of a Bonsai tree. The first one is the continuous root pruning of downwards growing roots. For the health of the tree it is advised that this is done over time to enable the tree to grow new roots in the place of the removed roots. A second method is done through air layering. This is simply done through preparing the bottom of the trunk as one would for air layering and heaping up the soil or packing sphagnum moss around this area. Roots will over time establish themselves in that area. I have read about a method where a wire is bound tightly around the trunk just above the roots. The flow of nutrients will be impeded and that will cause new roots to grow from above the wire. I have not tried this method myself before and cannot comment on how successful it is. Other methods include drilling holes through flat tiles and tying the roots of the tree in a horizontal direction to the tile with wire through the drilled holes. It could also be done through grafting.

In the end, the Nebari plays a vital role in the aesthetics of the tree. It is crucial thfotolia_2553306_XSat some sort of Nebari be established as it indicates age, shows that the tree is balanced and sturdy and has been there for a long time.

The next Blog will address the science behind root development.

Liverwort and Bonsai

IMG_0035Liverworts are flat growing green plants, closely related to mosses (Bryophytes). They have no stem and only a thallus, the flat leaf-like structure that is seen above ground. They belong to group called Hepatics and belong to the Marchantiophyta, a division of bryophyte plants, the mosses. These plants are primitive, not only in structure, but also in the fact that they are old. Some sources mention that they transition onto land during the Devonian Era (400 million years ago). Goes well with Bonsai then, I hear you say. Not really.

Bonsai growers will find these plants in moist areas. Where I live we have a high rainfall in winter and I have to be very careful with watering. This is usually taken care of by ensuring that the soil medium is free draining. Most of the liverworts that I see growing on soil come from nursery sourced plants, probably because the soil contains the spores and the fact there could be lot more organic soil in nursery plant soils.IMG_0032

The problem for me is that they can rapidly cover the surface of the soil and prevent water from penetrating the soil. This is not necessarily a problem as they already indicate that the soil is too wet. This layer of Liverwort can also prevent proper air circulation through the soil. I have also had experience of Liverwort growing over moss (I want the moss), suffocating the moss to death.

IMG_0034These plants reproduce asexually and sexually. They produce bumps (cupules) on the leaves, usually during late autumn, containing “eggs” called gemmae. These produce new plants. The sexual reproduction produces spores which germinate and form new plants.

As said, these plants can be an indicator that your soil or growing medium is too wet. If this is the case, it is obvious that the medium must be changed to be more free draining. Larger inorganic particles can be used to do this. If it is still a problem, look at the top layer of the soil. This could contain spores of liverwort. Scrape the top layer off and replace with a coarse material like gravel or pea metal.IMG_0035

Harsh chemicals could be used to spray on the liverwort to kill them off, but I have found that dabbing or brushing vinegar on the leaves of the liverwort, kills them off as well.