Прошлась немного поиском по иноязычному нету. В блоге у Walter Pall есть информация, приведу англоязычную цитату
"baked loam as main ingredient for bonsai substrate
I try to avoid the word 'bonsai soil' because there is no soil in modern bonsai substrate. I use for ALL plants that are in containes (bonsai, also the most expensive ones, flowers for the house and terrasse, tomatos tec.) 70 to 80 % of baked loam and 20 to 30 % of rough peat. Instead or in addition to baked loam you can take pumice, lava split, hard akadama (not the cheap one, because it decomposes and can kill your trees, crushed bar etc.
Baked loam is sold under many different names. Look for mateirals that are for tennis courts, addtion to soil for golf courses, sports lawns, material used by fire departments to pick up lost oil, material used in the building industry for insulation against cold and heat and for sounds. In America a product called 'turface' is fine. If you ahve a choice between the round particles and crushed ones always take the crushed ones.
In Germany a product called 'Maxit', 'Fibotherm' is OK. Use particle size of 2mm to 4mm. sometimes one gets a wide variation of sizes. Sieve your material and throw away everything that is smaller then 2mm."
(извините, но перевод не привожу - поздно уже и спать пора , нужное выделено полужирным шрифтом
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