Homemade compost is probably the best, but I use ordinary top soil from a big box with twice the volume of Pine Bark Soil Conditioner and a long list of amendments. The texture or tilth works for me in my environment where rain is neither to much nor too little season-to-season. It wets-out easily and dampness is evenly distributed. Perched water is only a problem in media that is watered too much or too often. That can be a function of automatic watering systems in which the size of pots affect the volume of water accumulated verses used, as in pots too big for a plant's use and/or the interval between waterings being too short, - for that size pot & tree combination. I water by hand with a hose looking at each tree and happily doing my thing, individually. Small pots in the shade use water greatly different than small pots in the sun, etc., etc. People who live in a rain belt like down south where it can rain every day for weeks, or on the Great Plains where drought and constant wind makes people adjust to that situation eventually find a mix that suits themselves.
I don't like rocks in my pots because they take up space and provide nothing for the trees to eat. It may be that the Japanese evolved to rocks because of their environment, -mountainous islands that are always close enough to winds that sweep-up moisture over the seas and dump rain as they rise up the mountainsides, just like the northern coast of California and Oregon and Washington and BC where the Japanese who introduced bonsai to America lived. That, and coniferous trees dominating collections, not to speak of yamadori. Trees growing on mountainsides are already in scree, so that's what they continued to use?
I stopped recommending my mix to others because there is no one media suitable for all, just like every place on Earth is slightly different than everywhere else. I guess that's why everybody seems to have a different formula, -and some are complaining it doesn't work for them. Whatever "it" is.
