Mick has contributed to the bonsai community with articles and demonstrations as visiting tutor for the AABC over many years and has donated bonsai to the NBPCA.

Over the past 40 years of bonsai I have learnt a little bit about conifer growing but unfortunately I reside on the far south coast away from the mainstream bonsai scene which in turn makes it difficult to impart it.  As well, quite truthfully I am no longer asked to speak or demonstrate anywhere as I am no longer on the AABC visiting tutors’ list.  My home group the Twin Lakes Bonsai Society has been wound up and I have formed a small group named ‘The Literati Appreciation Group’.

My first visit to Japan was in 1954, a ‘Nasho’ on the HMAS Vengeance, enroute to Australia with the 22nd Squadron from Korea on board.  Our last port of call was Yokosuka then a US Naval Base and I and my mate caught a train to Tokyo for a look.  It was still a mess; nothing was over one story high as there was no earthquake technology to build any higher then.  On the open streets covered with dust were bonsai.  I never forgot them and made my mind up then I would eventually learn to grow them.  I did much later, but am still learning.

My bonsai collection consists of pines, junipers, cedars and ficus.  Like me they are ‘old’ by Australian standards and some are big.  They have in the main (with the exception of the cedars and ficus which I collected myself) been grown from seed and cuttings. This year I will divest myself of most of my trees, keep a few I cannot yet part with and possibly try to grow a few shohin.

Quite truthfully I prefer Chinese punsai and penjing to that of the Japanese.  I have realized that nothing is perfect as is strived for in Japan and nature is not perfect in the Japanese sense of styling.  If I may say so, nothing stands perfect next to God and with your trees be better than nature but do not make a fool of it.  It now appears relatively common practice to place/bend a branch on a beautiful tree into an unnatural position so as to satisfy the stylist and viewers.  I abhor that practice.  It is way past tanuki or foxing or badgering [English translation to fox and badger]!  In any event, I want to write this time in the main about potting mixes and nitrogen drawdown. There could be a few add ons with my rambling.

As bonsai growers we do certain things to our trees outside of the usual realm of horticulture.  We remove the tap root of the tree!  This is nature’s anchor and we aim to substitute it with a mass of fibrous roots; the more the better.  Because of this, we can create instability and I have in the past always ensured my soil mixes contained ample heavy gravels to provide not only good drainage, but ballast to the tree in its container.  Also the gravel must be sharp as I have found the feeder roots of the tree will split when meeting the sharp stuff leading to more fibrous roots in the pot.  If the gravel is smooth and rounded the same roots will go around it without splitting, proceeding quickly to the edge of the pot and curling in turn causing root curl which is often seen in a badly slip potted tree. As well, most trees feed at their drip line where the feeder roots usually finish.  We grow trees in pots well short of their drip line when the tree has a wider spread than that of the pot.

I, like many other bonsai enthusiasts, have had trouble with curl grubs found in my containers often after the damage has been done to the feeder roots of the tree[s].  The grub is usually a scarab grub, but down my way can also be the larvae of the roller tiller beetle. Usually it is too late to save the tree when the problem is discovered. Unfortunately, over time, I have lost some valuable trees to curl grub damage and for this reason I then considered the use of “no soil” or “inorganic” mixes so as to reduce the risk.  I now grow in a mix of pumice, zeolite, diotamite, mini pine bark nuggets and coco peat.  I will on rare occasions add river sand and milled cow manure if I think the mix not right.  I made enquiries to Debco and some Sydney City Bonsai members and have received some feedback from Dorothy Koreshoff and Lee Wilson, and as well Grant Bowie and Ian Hearn have helped.

Some time ago when in Sydney to attend the Bonsai by the Harbour weekend I was fortunate enough to have some valuable discussions with some well qualified horticulturists who are very aware of the problem of nitrogen drawdown. There is definitely a tendency in Australia to use “soil less” mixes in bonsai.  This also applies in general gardening practices and insofar as bonsai is concerned we have witnessed the emergence of pumice, zeolite, diotamite, coco coir, coco peat and pine bark mulches in the form of nuggets, and various other grades down to fines. As well, akadama from Japan has appeared on the scene which obviously has the permission of our quarantine authorities.  Additionally there are the “usual” sands and gravels that have been used for some time.  Akadama, zeolite and diotamite, pumice along with scoria, sand and gravel can be said to be inert or inorganic materials while coir fibre, coco peat and pine bark are organic materials.

Pumice from New Zealand is imported into Sydney.  It is available in various sizes.  It is widely used in Hawaii and other US States.  I find it a wonderful and the best addition to my mix. Akadama from Japan is imported into Western Australia by Arthur Robinson, a known grower of Satsuki Azaleas.  Arthur and other users praise it highly.  They point out the Japanese have been using it for some hundreds of years and so should we.  I believe it is available from Scott Roxburgh of the Canberra Bonsai Society.  I have not used it and do not intend to.

Zeolite is readily available in various grades. It has a very good cation [pronounced “kat iron”] exchange.  Zeolite Australia was very informative and helpful.  In 2004 I wrote to Zeolite Australia seeking assistance.  I received the following reply; ‘From my experience with potting mixes you are very much on the right track. The 5mm gravel is basically an inert filler in your mix [my mix then] providing an open pore space, the zeolite used in its place will raise the cation exchange capacity of the mix and therefore hold more nutrients in the media. As it is porous and holds water it will increase the water holding capacity of the mix whilst not affecting drainage.  It is wise to begin with a half gravel half zeolite approach but it should not be a problem to move to 60% total zeolite.  The difference will be the higher nutrient and water retention which may alter the growth so observe carefully and record the application rates of fertiliser used.  You may find with the greater nutrient holding capacity from the zeolite that less fertiliser is required over time for the same rate of growth.  I have not grown bonsai myself but unlike other potted horticulture you may not be wanting an optimal growth situation rather than a slow controlled rate of growth.  The zeolite will also be helpful in buffering any ammonium in the cow manure as well as providing a store of ammonium, potassium, calcium, magnesium and the trace element minerals that will not hold in sand and gravel’. Zeolite have wished me well and asked for my results/observations.  Let it be said that since 2004 I have no wish to try akadama when I have an Australian product on my doorstep.

Mini pine bark nuggets are available in Sydney.  I buy mine locally from an Orchid Society.  If there is old product on hand I buy that as it is broken down.

The widespread use of wood based potting mixes has meant some changes in the way we fertilise.  Mixes containing bark etc are not stable and have the capacity to use nitrogen at the expense of the plant.  This feature is called nitrogen drawdown and is calculated as the nitrogen drawdown index or NDI. Mixes with an NDI of close to zero are those which have the greatest capacity to draw down nitrogen and are typically those containing pine bark or sawdust.

Additionally coco peat, also known as coir, coir fibre, is made from coconut husks, which are byproducts of other industries using coconuts.  It is used as a soil additive and is not fully decomposed when sold in block or brick form.  Coco peat will also use up available nitrogen [drawdown] competing with the tree. I have found that there are some contradictory claims made by some Sri Lankan suppliers of coco peat, pointing out that it is very high in nitrogen!  I am not sure these claims are correct as all information elsewhere points otherwise.

Diotamite, known as diatomaceous earth is now mined in Australia and is a sedimentary rock largely composed of the skeletal remains of aquatic plants called diatoms.  It is light in weight and has the capacity to absorb up to 200% of its own weight in water.  This is very useful to us.  When diotamite is incorporated into the soil, it serves to reduce compaction and increase the water and air permeation.  It also increases plant available water, firms soggy soils, loosens hard to work soils, provides better drainage, aids in nutrient transfer, and improves root growth. [As an aside, I have found that any diotamite on or near the surface of my pots will wash out, or blow away in a wind as diotamite is very light in weight]. Currently the available diotamite has lost favour as it tends to break up in the mix.

At the time of writing, I noted with interest that the NBPCA were using the mix of 2 parts diotamite, 1 part pine nuggets, 1 part zeolite and 1 part coco peat. I do not know if this is still the case in view of the stability of the available diotamite.  The NBPCA mix is equal to 60% inorganic and 40% organic. Grant Bowie advised me that the organic materials are used ‘straight’ from the pack and added Osmocote was put in the mix with a biweekly liquid feed of 10% – 14% of nitrogen.  It was pointed out that the most notable difference in growth of the trees was when Osmocote was not in the mix.  I personally do not fertilise excessively.

I did not attend the last visit of the late Peter Adams but asked an attendee if his experience with nitrogen drawdown could be discussed.  I understand Peter Adams’s mix to be 70% sand and 30% organic.  Unfortunately, I do not know what organic material is used but I was told he feeds the trees high in nitrogen during the growing season.

At present I am using a mix by volume of 3 parts pumice, one part zeolite, one part diotamite, 2 parts pine nuggets.  Note: this is until my diotamite reserves are used then I will increase the pumice volume to 4 parts.  As mentioned above I add the cow manure to assist with composting the pine bark, but I am not sure it is necessary.  This has not been done without experiment and last autumn I repotted a Monterey pine using the mix as a trial.  The tree is growing well.

In spring, when available I sparingly use two liquid fertilizers:

  • Brunnings “Nitrophoska”  – 16% N, 3% P  – slow release  and
  • Bloom N’ Grow “Cultisol”  –  20% N, 9% P, 17% K – water soluble

As well, seaweed based fertilisers are used.

I understand that many members of the Sydney City Bonsai Club use Dorothy Koreshoff’s coir and gravel mix.  I was told that this mix prevents the intrusion of curl grubs. I understand the mix to be 7 parts washed screenings (sharp gravel), 3 parts coir peat, 1 part standard Dynamic Lifter (no additives).

Ian Hearn [a grower of pines] on the North Coast now uses Debco ‘Plugger Custom’.  I have in the past had regular contact with Ian who advised that Plugger is used extensively in Coffs Harbour Bonsai.  It is available at Bonsai Environment, Sydney.  Debco Plugger is made with composted pine bark, coir fibre and mineral additives and has been pH balanced. Ian prepares his mix using a concrete mixer and said he removes the larger pieces of pine bark material during the process.  He reports good results, particularly with his pine trees.

I have never pushed the growth of my trees and have in the past fertilised sparingly and only when thought necessary.  The tree always tells you when and what it needs.  I liken heavy fertilizing to force feeding.  How would you, replete after a fine meal and asleep in bed, like to be woken at midnight and have a hamburger with the lot pushed down your throat?  I think not, but as I am now using new materials I have revised my ways after 40 years or so of bonsai cultivation.  I will not go overboard.
Remember there are black cats and white cats – they are different but they both catch mice. I am not sure if this is helpful, but I guess it is informative.  Hopefully!  I am a bonsai grower, not a continuous conference attendee and I am still learning.

Enjoy your bonsai!