If you ask 10 bonsai growers what is the best potting medium to use, you will get 10 different answers and possibly start an argument too. There is however an increasing usage of inorganic [non organic] mediums being used both here in Australia and around the world. Not just by back yard growers experimenting with substrates but also authorities on the subject who's trees are testimonial to the benefits of modern substrates.
The following article by Walter Pall [edited by Victrinia Ridgeway] is a very interesting and educational reference on the subject. It lays out the facts, benefits and importantly the potential dangers of using modern substrates for your trees. Before reading (and subsequently repotting all your trees) please pay particular attention to Walters advice "But one has to read quite carefully and then do EVERYTHING".
This article has been reproduced with WP's permission from His blog - Walter Pall Bonsai AdventuresWalter Pall wrote:Substrate, watering and feeding cannot be seen as separate. Each is connected to the other and so it becomes quite complex. Be it a deciduous tree, conifer, young, old, recently potted, or even collected, there are so many variables inside a bonsai garden. Can there be a clear answer?
Well, yes. But one has to read quite carefully and then do EVERYTHING. It is not feasible to pick one that you like and ignore the others. You cannot feed according to my method and don't care what substrate you have or what your watering regime is.
First, I set aside everything that has been written in most bonsai literature about the subject. As technology grants us access to new and more effective methods and products, the way we care for our trees has progressed beyond the boundaries of tradition. It has been a new and modern world for some time, but many have not realized this. Even if some measure of success is achieved with the old methods it can be dangerous if used with modern substrates and practices, or even deadly.
Substrates: Good substrate material must: be of equal particle size, have the ability to absorb water and release it back, have no fine particle organic material, must not decompose easily, be as lightweight as possible when dry, preferably inexpensive and should have an aesthetically pleasing appearance. This would then be: lava, pumice, baked loam, Turface, zeolite, Chabasai (a type of zeolite), coconut pieces, bark pieces, Styrofoam pieces (no joke) and a few more which you can find yourself if you have understood the principles. Please note: Some of these materials may not be available in your area.
Normal akadama is questionable as a good substrate as it inevitably decomposes, especially when exposed to winter frost. It can become deadly loam in the pot, choking the flow of water and air into the soil. This is especially true for trees which are only rarely repotted, like collected conifers and old bonsai in general.
Substrates which are not useful: soil, compost, stones, sand etc. Trees grow in sand and flower soil, of course, but it is not an optimal growing medium for health in bonsai culture.
All substrates can be mixed according to your liking and it makes almost no difference. They can also be recycled and used again, but make certain to sift and clean any recycled materials as needed.
There is no such thing as an 'ideal bonsai substrate'. There are in fact thousands of ideal substrates. I believe that IT DOES NOT MATTER WHAT YOU USE AND IN WHAT MIXTURE as long as it is a modern substrate.
Since there is no soil in modern substrates there is very little alive in them. They dry out easily and one must water several times a day when it is hot, especially if you have used pure inorganics. Therefore I add rough peat in addition to the previously mentioned substrates. This is the kind of peat that is harvested in bogs and comes in its natural coarse form. Make certain not to use fine particle peat/sphagnum moss, even if the package says “dust free” as the particles will be too small. If you cannot find the correct type of peat, use small bark bits without dust particles, or cut coconut fibers. These organic components should comprise 15-20 % of the overall volume, a bit less with conifers, olives and such, and a bit more with small trees and azaleas.
These organic materials are good for keeping humidity higher in the substrate and for supporting the colonization of beneficial microbial life in the soil composition. Research also seems to indicate that peat moss has plant hormones which are good for trees. These are organic materials which would normally have no business being in a bonsai substrate, but the ones mentioned take five years to decompose. You have to consider this when planning your repotting schedules. The organic material should also be sieved out of any substrate that is being recycled.
Watering: I have a watering schedule that runs from the end of March to middle of October EVERY day. This is regardless of whether the trees appear to be dry or not. Only when it rains heavily will I refrain from watering the trees. When it is hot, or there is strong wind, or a combination of the two, I water two or even three times in a day. Very small trees must be watered twice a day. ALL trees are watered the same. Individual watering habits are not needed when all of your trees are in a consistent well draining substrate. There is also no need to carefully train a friend how to water your trees when you are away. Any person can water the trees; everything must only be watered thoroughly. It also does not matter what type of water is used. Tap water is very usable for all plants, even if it is hard water. I have some of the hardest water in Europe in my garden (23° DH). I use this water for everything, including azaleas. I water with a garden hose, full speed. I do not water individual trees, but areas, just like you might water your garden with a sprinkler system.
When you water this way, water aggressively. This means everything becomes very wet, the whole tree from top to bottom. The water must run out of the draining holes. It is very good for the trees if the crown gets wet every day.
With modern substrates over-watering is almost impossible. You can water for hours and all of the excess will just run through the pot if the correct substrate is used. It is very easy to under-water though. Many bonsai die because they are sitting in modern substrate but are watered according to the old methods - under-watered in fact.
Feeding: With modern substrates and aggressive watering, feeding is no secret anymore. ANY fertilizer that is offered for ordinary plants can be used, whether organic or chemical. Fertilizers should have LOTS of nitrogen. Only with nitrogen plants can grow.
I use mainly liquid fertilizer that I get from our cheapest general discount market. In America it would be Walmart. Use general fertilizer that is noted as being good for all plants. In addition I buy a few dozen boxes of granular fertilizers which contain chemical and some organic ingredients. Two times a year, in the beginning of May and in the end of August, I throw a handful of dried chicken manure at the trees. I buy this in large bags, which is very inexpensive. That's it. For ALL of my trees including the world famous ones I use the same fertilizer.
How much? WAY MORE THAN YOU THINK! I feed from 20 to 60 times more than the average bonsai grower. From the beginning of April to the middle of October, every ten days everything is fed with liquid fertilizer, using three to four times the suggested dose. All trees are fed equally, whether deciduous, conifers, small, large, repotted, collected or not. This is a span of about 200 days when the trees are being fed. Since the trees are fed three times the normal dose on twenty days in that time, it makes for 60 doses of fertilizer in the growing season. The average bonsai grower feeds maybe three or five times at half the normal dose because 'bonsai trees should not grow'. If you then add two times a year of chicken manure being given to the trees, you can then understand why this schedule is 20 to 60 times more than the average.
Asian fertilizer cakes are fine but superfluous in our culture. We don't eat steak with chop sticks and don't have to feed plants with cakes. But they don't hurt if you insist of using them; they are just unattractive to look at. Biogold was made to be used with modern substrates like akadama, and it works well. If you give it to me I will break it into very small particles which I then throw all over the substrate surface of the trees. After one watering it becomes invisible.
Too much salt in the substrate is almost impossible if one waters aggressively every day. Even azaleas don't mind my treatment. They thrive very well with very hard water, ordinary baked loam and peat as the substrate and aggressive feeding like all the rest of the trees.
About ten years ago 'super feeding' was proclaimed and a while later forgotten. It did not produce the expected results and many trees suffered and even died. What I do sounds similar. Well, it is similar, only that I insist on aggressive watering in parallel to aggressive feeding and the use of modern substrates. I also don't make the ingredients of fertilizing trees into a science. I tell you to buy whatever is on sale in the garden center or agricultural supply store.
This feeding scheme is for trees in development. Remember that 99.8 % of all bonsai are 'in development'. If you happen to have one that should really not develop anymore you slow down its feeding schedule considerably. You let it starve on purpose. Then it will get smaller, and fewer, leaves and needles. It will look good for shows, but your tree will go downhill if you continue to do this for too long. After a few years you have to feed it aggressively again to let it recover.
Summary: Do all three or nothing! You have no choice here. To just pick one method and refuse the others will end in disaster. Those who do 'super feeding' using old-fashioned soil, and insufficient watering will kill trees. Those who use modern substrates, aggressive watering and fertilizes like the old days will have very weak and, in the end, dead trees. That's all there is to it.
So the question, “How do you feed conifers?” Gets the answer, “Like all other trees, but you have to know the whole story.”
I know that many will not believe this. ‘He who heals is right’, is a saying in human medicine. In gardening 'he who has the healthiest trees in the long run' is right. Come to see my garden or look at my gallery, they speak for themselves.
All this was not discovered or invented by me. I only learned from professional modern gardeners. They have done this for decades with great success. I have adapted modern horticulture to bonsai. Only in the bonsai world does this seem revolutionary.
Walter Pall
For more information and discussions on the topic of substrates, please see the following threads on AusBonsai;
Inert Growing Medium
Grit of various types and size
Diatomite and similar properties testing
Potting Mix Tests Results Abbreviated
Soil mix test results
Soil mix test results 2
Happy reading and research
Regards,
Steven
Pup
) can be found here - 
That would be 120-160ml of Nitrosol to a 9 litre watering can 
