Yeah... I gather the answer is simply too complicated to even worry about. Just give them your native soil and that's as good as anything else we can figure.
A Ph of 4.5... that doesn't seem natural. I wonder if that's a condition created by semps to discourage roots of other plants.
On the other hand... I do wonder what are the optimal conditions for Sempervivums. I often think the mountain crevices are not optimal but rather survivable habitat for them. A place not survivable for most other plants. Would they actually flourish much better down in the valleys if not for the many aggressive shrubs, trees and weeds that would choke them out? Plants that cannot survive in those alpine environments. Do we not feed them Nitrogen although there would be precious little in a rocky crevice. They seem to like that. Maybe they would love some more Ca in my naturally Ca-deficient soil. I seriously doubt it would bother them even if it was needless. I would think the weathering rocks in an alpine environment would provide a good deal of Ca. So much I don't know.
