Yes, soil is definitely not allowed to be brought in. Years ago I was visiting Kakteen Haage in Germany, Haage was one of the old Epiphyllum hybridizers and there is also a cactus named after him. There were several greenhouses with Epis alone. To bring some into the USA would have been possible, bare root, treated with all sorts of stuff and then certified. For a special fee which just made you give up right then and there.
I am not sure if bark falls into the same category, it probably does too, but Sphagnum does not. Ecuagenera wraps many of their plants with that and then wraps them tightly with paper.
