Joe, though I custom mix all my own potting soils, a typical houseplant mix you can use is 1/2 general-purpose potting soil (Miracle-Gro, Green-thumb, etc), 1/4 coarse perlite, and 1/4 medium fir bark or cypress. I want a soil that will hold a bit of moisture but at the same time is very well-draining. I am sure, if you asked a half dozen tropical plant growers what to use, you would get a half dozen "recipe's'. Rubber trees grow fast, and their roots are notorious for growing out of the drainage holes. Though they are trees and flourish when given strong, indirect light, they are very forgiving when it comes to lower light conditions. With less light they just won't grow as fast and the leaves might not be as dark-green. Rubber trees are a great houseplant.
