Ahhhh the deepest questions of Life. So many possible answers, and no perfect one.
Are you reading
this thread? Lots of good information here, including the organic/inorganic suggestions for different trees, and why they are important.
As Will points out, you could grow trees in glass shards if you paid enough attention to them and gave them adequate water and ferts. Perhaps for the greenhouse, with controlled conditions and generally similar plants, one perfect soil could cover it. After all, in greenhouse growing they want the lushest plants so they give them lots of fertilizer. The plants are climate controlled and watered on a schedule. We, on the other hand, and bringing in trees from the deserts or from the swamps. We can't control the climate or humidity, and we don't always want the lushest growth. We want controlled growth.
Joanie