I'm gonna have to say that a lot depends on the plants that you wish to grow then and the all-rock substrate that you wish to use.
Sorry, having a little confusion replying here to Q's in the other thread as well--
Yes, of course, you can incorporate hypertufa into the design--if you can make it or get it--and plants can actually grow right in the real thing or the fake thing, but they will not grow right in field stone, for example. well, okay maybe some mosses, algae and lichens will, but I presumed that is not quite what you had in mind. Slate, in my experience, depends on how flaky it is really, but there the plants/roots are growing in the crevices between flakes not actually in the rock, or roots are behind the rock in the medium in the case of a dry-stack-wall. Some lava stones and some sand stones, with 'built in' crevices have worked pretty well for me with some weeds.
