Fungi play a vital role in soil health and plant growth through symbiotic mycorrhizal relationships. A sterile soil is nearly impossible to achieve and maintain, and may not provide the benefits of a diverse soil microbiome including fungi. The document discusses the complex relationships between plants, fungi, bacteria, and other soil microbes, and how they breakdown organic matter and cycle nutrients to support plant health. It questions the practice of using sterile soil for bonsai cultivation.

1. WHAT SHOULD BE IN YOUR
BONSAI SOIL?
Bio-Activity and Bonsai Growing Media.

2.  Having been immersed in my own little world of
growing bonsai for so long now I have picked up a
few things. Some of those things could be
described as newfangled, revolutionary or even
cutting edge. However the modernization of many
bonsai cultivation techniques is long overdue. The
existing tome of ‘wisdom’ is so firmly rooted in
ancient history that any new idea, no matter how
simple, can be construed by some folk as
incendiary. When you spend your time entirely
immersed in something, as I have, it’s inevitable
that you learn a few things. The more things you
learn the more you see and the more you see the
more you begin to realize what is…..

3.  1.wrong with what we currently do and….
 2.what we SHOULD be able to achieve.

4.  The word KAIZEN is a Japanese word that, in it’s simplest form
means ‘continual gradual improvement’. The primary connotation
being that the way we are currently working is the worst solution. By
applying a modicum of common sense and expending a little effort
we can make considerable advancement in our technique and the
results it produces. As an example, starting a car engine with a crank
handle was all very well but it did offer a few disadvantages. For it’s
time it made sense but only a Luddite would choose it over a modern
starter motor. Keeping warm around an open fire, burning in the
middle of your living room, was the norm way back before some
bright spark invented the chimney and the anti-smoking movement
came into existence. Change is the only constant in life unless you
practice bonsai where the norm is to not change anything. ‘If it ain’t
broke’, the oft’ repeated mantra of the unindustrious, bone idle and
somnolent seems to apply here. However in my experience it IS
‘broke’. I just cannot comprehend why anyone would want to spend
years doing something like bonsai and be perfectly content with
skuzzy half-arsed results, especially when there are dummies like
me out there who are prepared to share all we know for free. There
really in no need to reinvent the wheel we just need to put a tyre on
it!

5.  As I said at the beginning, putting together a new idea is a
process with a circuitous path. I tend to get a feeling that
something is going on upstairs, often long before I see
anything. It’s not unlike getting a teenager out of bed, even
though you know there is life up there you have absolutely no
evidence to support the notion. I have always found that once
I become aware my old grey matter is cooking something up
it’s not normally very long before it hits the table. This event
can be triggered by the strangest of events. Two things
happened recently that caused an avalanche of information
my mind had been cogitating for a long time. The first was a
discussion with a customer about fruit flies and the other was
a gift of wild mushrooms from one of our delivery drivers.
Later I was having a discussion about soil selection and, not
unlike a Monty Python sketch a fully formed conception
dropped at my feet. In order to flesh out some of the details I
decided to write it down as best I can so here goes……..

6.  Conventional wisdom states that bonsai trees should be
planted in sterile soil. The reason being that using sterile soil
will prevent the ingress of pest and disease (P&D). Not an
unreasonable idea. The notion, as so many other things in
bonsai cultivation, has come from mainstream horticulture. A
sterile growing medium has a few uses in horticulture such as
seed germination, striking of cuttings and a few other
technically demanding activities. However the practicalities of
sterilizing large volumes of growing media make use of such a
product an expensive proposition. Modern composting can
sterilize soil as bacterial activity can generate high
temperatures. The primary benefit however is the destruction
of weed seeds. Garden centre’s do not want to spend lots of
time weeding pots. However if you were paying attention you
noticed that it was the bacterial action within composted
material that generates heat, therefore the soil is not entirely
sterile.

7.  The growing media we use in bonsai cultivation
however is not, as a rule, soil. We use a variety of
natural and manufactured aggregates and organic
products like chipped bark etc’. Many of these are
easily sterilized or are sterile as a part of the
manufacturing process. So to a degree it would be
possible for us to use a sterile medium. However
unless you use sterilized water and keep the plant
in a sterile environment the soil will be
contaminated as soon as it comes into contact with
the atmosphere and water. So, the notion of
sterilized soil is…..
 Very hard to achieve and….
 Virtually impossible to maintain.

8.  In light of the above it’s easy to see that a perfectly
sterile soil is almost impossible to achieve and
absolutely impossible to maintain long term.
However I have to ask the question, is a sterile soil
really necessary? Are there any significant benefits
to using such a medium? What are the potential
down sides? Are there any benefits to NOT using a
sterile soil mix?

9.  This brings me to the gift of mushrooms I received. As a kid
our house backed onto a huge school playing field. Every year
I spent the latter half of the summer holidays tramping around
the field collecting vast quantities of mushrooms that grew
there. However it’s been thirty five or more years since I last
did that. The gift sparked my interest and so the next time I
took the dog out to the woods I gathered up a bag full of
different ‘shrooms’. My friendly delivery driver helped me
identify more than a few but that left me with a large number
we couldn’t figure out. So, as I do, I headed to the interweb
and that helped me with a few more and also led me to a good
old fashioned book. In the introduction I learned a VERY great
deal about fungi and their fruiting bodies, mushrooms.
Mushrooms and toadstools are exactly the same thing, a
generic term that applies to the fruiting bodies of fungi. The
appearance of such things in a bonsai pot is enough to cause
an instant coronary in many bonsai growers and cause them
to run, sweating, to the shed to break out the Armillatox.

10.  Many bonsai growers are aware of the fungi that lives in the soil with
pines, often referred to as mycelium. We know this is a sign that things
are good but why? Also should we be seeing this with other plant
varieties? Just to be clear an hypha (plural hyphae) is a long, branching
filamentous structure of a fungus. In most fungi, hyphae are the main
mode of vegetative growth, and are collectively called a mycelium.
Hypha develop into a fine web like net through the material from which
the organism gains it’s nutrition whether that be rotten wood or the root
system of your bonsai tree. Most of these organisms are not visible other
than with the use of a microscope. A single gram of garden soil can
contain a million fungi. The type of fungi associated with pinus species is
coarser and more abundant than some others and so we can see it. In
order to produce a fruiting body (mushroom) two mycelia of the same
species band together in the equivalent of a sexual stage. Then, given
the right conditions of nutrition, humidity, temperature and light a fruiting
body is formed. Then, given sufficient water, a mushroom is produced.
Some fungi are parasitic and can cause the demise of their hosts.
However here we are referring to what is commonly called Mycorrhiza,
those fungi that are able to live with plants, creating a relationship that is
beneficial to both (from myco meaning fungal and rhiza meaning root).

11.  Fungi are the third kingdom (Linnaeus), just as
important as animals and plants. Fungi are a very large
classification of organisms which have similarities to
plants but they lack chlorophyll and are unable to build
up carbon compounds essential to life. Instead they
draw their sustenance ready-made from living or dead
plants or animals in exactly the same way as we
animals do. As work on the ecology of fungi progresses
we are beginning to realize that the world of plants is
incredibly dependent upon fungi in every sense of the
word. Fungi break down leaf litter and dead wood and
ensure the surface of the world has a fertile layer of soil.
However it is through the intimate relationships between
fungi and the roots of trees and plants that the most
important contribution of fungi is made.

12.  Trees and woodland live in a symbiotic relationship with a vast
number of fungi and were it not for the help given to the plants
through these relationships many woodland areas would
simply cease to exist. If fact, without the third force of the
fungal world, life as we know it would not be possible, either
for plants or the animal kingdom that is entirely dependant
upon them. Virtually all plants develop mycorrhiza
relationships. It is thought that only about 5-10% of plants
function without some fungal help. It has been calculated that
there are over seven THOUSAND species of fungi that form
mycorrhiza relationships with a similar number of plant
species. Within this symbiosis the fungi receives carbon from
the plant and in exchange passes phosphorus, nitrogen, zinc,
and a greatly improved water supply back to it’s friend. The
supplies are passed through the mycorrhiza tips to the plants
roots. It has been calculated that in the region of eight million
tips are needed to form one small mushroom.

13.  N.A.S.A (North American Space Agency) have been investigating
the effects of fungal symbiosis for about fifty years. It carried out
a long term, controlled experiment by planting a pair of young
pines, both 1 meter tall, in very poor soil: one with a sterilized
root system, was planted in sterilized soil. The second was
infected with one of the Amanita species of fungi and planted in
unsterilized soil. Both plants were observed and kept under
controlled conditions for some 15 years. When the experiment
was concluded, the sterile specimen had grown to just over 1.5
meters in height: by contrast the infected specimen had grown to
8 meters in height with a trunk more than 35cm in circumference.
This graphically demonstrates the value of fungal symbiosis.
Some time ago we took three large serissa bonsai and bare
rooted them all. One was planted in sterile akadama. The other
two were planted in our No1 and No3 Bonsai soils that are
extremely bio-active. After a full growing season the one in
straight akadama had begun to discolor and shed fine
ramification and lower branches. The leaves were also smaller,
softer and paler in colour. I think we might be onto something
here….

14.  Symbiotic fungal relationships can make the difference
between life and death to plants and trees, particularly those
planted in less than ideal conditions. Also bear in mind that if
the plants fail the fungi go with them, neither will survive
alone. Forest clearance can change the fungi present in soil
with the result that fungi disappear. Therefore, attempting to
replant forest regions may not always be successful. That’s
one reason why, when ancient woodland is destroyed, it can
never be reinstated. In the ancient past areas like Scotland
were predominantly covered in beautiful woodland but
following deforestation it is impossible to restore the habitat.
We need to be aware that the fungi present in ancient
woodland systems have built up over thousands of years and
destroying the habitat by clear-felling will damage the whole
delicate ecological balance. When you consider what our
bonsai have to go through is it any wonder so many trees are
left struggling? I speculate that once we learn more and take
heed of these facts we can dramatically improve the growth,
health and development of our bonsai trees.

15.  So, to summarize the above. We know that plants are the basis of all life
on earth because they take water, oxygen and sunlight and create
carbohydrates that are used as an energy source by other life forms that
can’t perform this clever trick we call photosynthesis. Fungi cannot
produce their own energy source and so get what they need from plants,
However unlike humans they are not greedy or inconsiderate because
they give back in equal measure. In relation to the soil in which it grows a
plants root system is very coarse and not overly efficient at gathering the
water and nutrient it requires. Fungi however are infinitesimally small and
are spectacularly efficient at getting the best from the soil. However,
perhaps surprisingly to some, there is no ‘goodness’ in the soil, just raw
materials. In order to make use of those materials you need a chemical
factory to turn them into something useful. Fungi have just such a facility.
They don’t own it, they didn’t build it but they do work hard to keep it
working day and night for their own survival and much like a modern
chemical facility it’s called a plant. Fortunately for us there is also enough
left over for us too, at least there is until we destroy the whole system.
This relationship between a plant and a fungi is called a symbiosis and
both benefit enormously from it. As we can see fungi are vital to all life on
earth so what in the world would cause someone to think that bonsai, or
any other cultivated plant, should be kept in a sterile soil?

16.  At this point it’s important to consider another level of activity within a
healthy soil we could refer to as soil fauna. Soil is a word used very
loosely but it refers to “the upper layer of earth in which plants grow, a
black or dark brown material typically consisting of a mixture of organic
remains, clay, and rock particles”. So, a complex mix of elements are
required to create something we can call soil, it’s not just a growing
medium but a whole eco’ system. I hate using the word soil to refer to
horticultural growing media because it has become such an ambiguous
term. As we have seen, one large element of a balanced and healthy soil
is the fungi that live within it. However in order to create soil in the first
place, and to maintain it’s health long term, we need large volumes of
organic material which ultimately becomes ‘humus’, another ambiguous
and mis-understood term. Organic material from plants and animals falls
to the soil surface known as the soil-litter interface. Here the activity of
soil organisms break down the material. For sake of simplicity consider
these levels of activity like a sieve. Larger organisms break down waste
that is progressively passed to smaller organisms and so on until we
reach single celled organisms we call bacteria. Once they have finished
with the material we have humus. This atomically binds to aggregate
particles within the soil turning it the familiar dark colour and providing a
negatively charged coating that attracts and holds chemicals needed for
plant growth. These are what the fungi pick up and pass to their host
plant and so the circle is complete.

17.  Soil fauna consist of earthworms, nematodes,
protozoa, bacteria and different arthropods, not
forgetting fungi too. Without these life within soil is
extremely difficult for plants. So, not all creepy
crawlies and fungi are bad for our bonsai, in fact
most are very good. If we can keep our trees strong
and in a healthy natural condition they will be
resistant to the advances of their natural enemies.
Hopefully I have set this out clearly enough that it’s
plain to see, breaking the chain of events will cause
us dramatic problems. Evidently we may need to
adjust some of our techniques if we are to take
advantage of this situation.

18.  When I studied horticulture we covered a wide range of subjects and
different disciplines. When it came to pot culture of plants it was made
plain that this was one of the more complex and difficult areas of
horticulture to master. Now bear in mind that in commercial horticulture
the primary reason to grow plants in pots is so they can be easily
transported for localized use or sale. A small plant in a pot is a very nice
little package. However most of those plants are destined to be either
short lived as would be the case with vegetable or fruit bearing plants like
tomatoes, or planted out into open ground as with most garden plants.
Very few commercially produced potted plants are expected to remain in
their pots for decades as is the case with bonsai. So, we have taken one
of the more difficult aspects of horticulture, pot growing, and done that
with very large, very old plants and put them into entirely unsuitable
small, and worse still, shallow pots. These are often grown by folk who
have very little background in horticulture and also fancy themselves of
an ‘artistic’ bent. It’s a bit like giving a small kid a box of matches and a
box of fireworks. Given a little time it can all go horribly wrong. So what
can we do to take advantage of a natural phenomenon that is right
beneath our feet?

19.  Obviously our primary consideration is to select a soil or
growing medium that is going to be beneficial to supporting a
dynamic and biologically diverse rhizosphere. This is a
spectacularly complex job requiring a lot of knowledge,
understanding and experience. I have laid out the basics in
my article on Choosing Soil for Bonsai. We have also
developed an all encompassing range of soil products you
can use right out of the bag to save you all the head ache and
heart ache of costly experimentation with your prized bonsai.
It never ceases to amaze me why folk in bonsai, some of
whom have very expensive trees, insist on finding the
cheapest growing media they can, it’s just such a false
economy putting your thousand pound tree into cat litter
because it’s a pound cheaper than something that can
produce VASTLY superior results. It’ like putting cheap tyres
on your 200mph super car, sooner or later it’s going to go
horribly wrong. Lesson No1 DON’T BE CHEAP! It makes you
look bad and your trees will end up looking worse.

20.  Good bonsai soil will have a high degree of bio-activity built into it. It will
also have the ability to hold nutrients, maintain drainage, hold moisture,
prevent capillary action, have the mechanical strength to survive for long
periods and provide increasing space for a developing root system
without causing compression. It will also need an almost infinite structure
of micro pores in which to provide a moisture reservoir and a foot hold for
all those lovely fungi and bacteria. Also don’t forget that after a few years
it will need to come apart and release roots without damage when you
come to re-pot your bonsai. Sorry to say there is not a single product you
can buy out there for peanuts that will do all of these things. Even many
traditional products used for bonsai fall seriously short, products like
John Innes mixes, horticultural grit and even Akadama only give very
poor results at best and can cause the demise of plants in less than
extreme circumstances. After 25 years of cultivating tens of thousands of
trees I can honestly say that the most suitable medium available in the
UK toady is our own soil mixes. These are constantly being improved
and refined to give the very best overall performance possible cultivating
the widest range of bonsai in UK conditions. Maybe in time there will be
a breakthrough and we will all go over to using something else but for
now that’s not even on the horizon, if it were I would have trees growing
in it.

21.  Having decided upon our suitable growing medium it’s important to consider how
we get our bonsai into it. I have covered bonsai re-potting technique extensively
in Graham’s Guide to Repotting Bonsai Trees. The best growing media in the world
will be of little benefit if 80% of your plants rootball is an impenetrable brick of
compacted old akadama or similar. A bonsai lives in a very small amount of soil
and it’s important that ALL of it is available for root development, moisture and
nutrient supply and the provision of air to the developing roots. I will deal with the
subject of compacted root systems in a forthcoming article but for now the idea of a
new inch of soil around the outside is not acceptable. When re-potting bonsai
ensure the rootball is dry before you start, dry soil comes away much easier than
when it’s soggy and wet. NEVER wash the roots of a tree because this will carry
away the seeds of a beneficial community of bio-active colonies that are vital to the
re-establishment and long term health of the plant. If you decide to use a product
likeRootgrow bear in mind it will be wasted if you are using pure aggregate
products like cat litter, akadama, kiryu and their ilk. These types of product simply
don’t have the mechanisms in place to support the fungi that such valuable
products contain. Finally, after re-potting only give the soil a very slight watering.
Pouring water through the soil until it runs clear out of the bottom of the pot may
seem on the face of it to promote drainage but if you are using that all important
bio-diverse soil medium what do you think is being washed out of the pot? After re-potting
bonsai ensure the soil is just damp throughout and try to keep it that way
until full growth resumes. Cold wet soil discourages bio-activity and severely
retards the healing and subsequent development of new root mass. Also if there is
a lot of water held in the soil there will be less oxygen available which, at this stage
of the re-potting process, is more important than a copious water supply.

22.  In order to maintain a bio-active bonsai soil mix and healthy rhizosphere long term
a few simple points need to be observed. The most important factor being only
ever use organic fertilizers. Chemical fertilizers are too aggressive for bonsai, they
work great for fast growing plants like tomatoes or bedding plants but should be
avoided for bonsai use in my opinion and experience. I already mentioned the
fauna required for the development of a healthy root zone and many of these live
on what is called the soil-litter interface, the surface of the soil. In a bonsai context
this is the top half inch of soil including the area from about half way through and
moss covering down into that top layer of growing media. These incredibly diverse
array of organisms produce a valuable service in breaking down organic material,
including fertilizers, so that they can be accessed by bacteria that in turn release
nutrients that plants can access. If you take an inorganic fertiliser such as
Tomorite, an oft recommended product for bonsai, and mix it for use. Then swill
your hand around in it for a few seconds you will likely be surprised just how much
it stings your cuticles and will hurt like an S.O.B if you have any tiny little cuts.
Imagine pouring that into your bonsai pot, all the life in there will be covered until
next time you water. Keep chemical fertilizers out of bonsai all together they don’t
bring anything to the table that’s not available from a good quality organic product
like Green Dream Original. I will be covering the subject of fertilizers in a future
article but at this juncture it’s worth pointing out a few things in relation to the use
of organic products.

23.  Organic fertilizers are made from nutrient rich ingredients. These require
the activity of soil fauna to release them. This often results in a covering
of mould and a few creepy crawlies all going about their important task.
In the case of fertiliser pellets this can even result in the colonization by
maggots for a short period of time. These are all wonderful pointers to
the fact you selected a good quality product full of nutrients and that it’s
working as it should. Products like Bio-Gold are treated with a strong
pesticide to prevent all this taking place and is not, in my opinion, worthy
of the title organic. Fertilizers should only be used when the temperature
is constantly above 12° Celsius. Below that most root activity and cell
division ceases and even if some activity takes place it will not be
requiring nutritional supplementation. Our rule for spring is 12° for 12
days before we give the first feed. Always choose a product with a
multiple nutrient source. Products like chicken manure (shit) are single
source and are very poor fertilizers containing low levels of nutrients,
often in a very narrow band and missing lots of vital micro elements. A
great supplemental feed for your fast growing vegetable crops but not for
bonsai. A good product like Green Dream will contain diverse sources of
nutrient bearing compounds from bone meal to seaweed. So a little
smell, a little fuzz and a few little animals taking advantage of the bounty
is all a part of the bio-activity and diversity our bonsai trees so
desperately need.

24.  Just one last point to consider and that’s the use of ‘soil pesticides’. A very great deal of
commercial activity is developed on the back of fear. Just take a look around you. We are sold
products all the time that in reality do very little, if anything at all. Products to stop us looking
older, to make us more popular, more energetic, fitter, healthier etc’. If you could produce a
product that a nerdy, spotty teenager could spray on himself in order to attract beautiful girls do
you really think it would be for sale for a couple of quid in supermarkets? I have yet to find a
bonsai grower who does not turn sickly green at the sight of a vine weevil. But, let’s just think
about it in the cold light of day. The hype around these little critters has come from nurseries
that grow soft tissue plants. These types of plant are grown en-masse in huge commercial
establishments raising tens of thousands of the same plants, normally in the cheapest nasty
wet compost available, after all a lot of water means a bigger plant which means more bucks. If
you had never laid eyes on a mature vine weevil and just relied on the reputation it has in
bonsai circles you would imagine something the size of a lion with the hands of a huge mole
and a wood chipper for a mouth. In reality it’s a crunchy little beetle that can neither fly or swim
that matures from a little grub smaller than the average maggot. They love multi purpose
compost and peat based substrates because they are easy to burrow into and support a lot of
fleshy root growth upon which they feed. In practice you may find a weevil or two when re-potting
but seeing as they don’t eat wood and only live on fleshy roots and are a few millimeters
long how much damage can they do? If you grow begonias and the like I would be careful but
in bonsai cultivation over 25 Years I have never seen any damage inflicted by these guys
sufficient even to mention. Also bear in mind that they are now firmly established in Britain’s
carefully manicured lawns and grasslands and are here to stay. The best line of defense is to
choose a good bonsai soil mix at the outset and they will soon meander off to find easier
pickings. Using soil application pesticides really should be avoided unless you have a more
serious and persistent infection of something like root aphid. If we can maintain a good healthy
balanced rhizosphere harmful pests will either never appear or be kept in check by everything
else that’s happening down there.

25.  To sum up, I think that as kids we are taught to fear a lot of
things in order to keep us safe. Mushrooms are bad, well
some are but a great many are not and provide some good
eating, but do take the time to learn which is which, ignorance
can kill. We are also taught that bacteria is bad, the exception
being those stupid little bio-pots of yogurt that, judging by the
price, must contain some alien life from a distant planet. I was
also led to believe that if it smells bad then it must be bad. My
dog eats raw tripe every day and that smells pretty bad to me
but he loves it and is the picture of health. French cheese can
smell pretty bad too but they seem to like it. So not all bad
things are bad for everything and some good things are bad
for other things. We need to keep our ideas in context, think
these things through, clear out the commercial nonsense and
develop a way forward that works for, in this case, our bonsai
trees. A healthy bonsai tree is a happy bonsai tree and a
happy bonsai tree makes for a happy owner and now I am
getting a bit confused and need to go buy some of that nerdy
spray.

26.  Graham Potter.
 http://www.kaizenbonsai.com