bisco_bonsai

I don't see why starting with sterile soil would be good for most nusery plants and bad for bonsai. With exposure to the environment, I'm sure the sterile soil will not stay sterile for long, but it's a good place to start, providing that appropriate fertilization is given to the plant. Lastly, I'm not sure which would be better, adjusting your soil to the specific tree, or adjusting your watering to the specific tree. To me, I think intuitively I wouldn't give a pine as much water as say a maple. Adjusting the soil for all my trees so that I can water them as a group seems like a good idea at first, but I think a nice consistent soil mix across species that will perform just as well for each might have its merits. Of course, adding a little more grit or bark here and there to accomodate a specific species wouldn't be so bad after all.
All the best,
JDL