At our recent bonsai soil workshop, members had the opportunity to create their own mix using a number of different ingredients in different proportions for different types of plants. Several of these ingredients seemed similar in their funtion; for example, haydite, turface, pumice, granite, lava rock have similar properties and should therefore, one would think, be interchangeable in a formulation; soil, compost, leaf mold also share similar characteristics.
Why would one want to use one rather than another?
On what is such a decision based?
Why is one percentage of an ingredient appropriate whereas another is not?
Is there such a thing as a good all around formula for all bonsai trees?
Do we need to distinguish between evergreens versus deciduous versus tropical, ... based on what?
Why do some members swear by a complete inorganic mix whereas others use significant proportions of organic matter?