Paleo,
The gravel distributor near my garden sells big sacks of dolomite gravel and it comes in some very fine sizes which border on sand, I've been very tempted to try it out but wasn't sure if there would be a big benefit of using it over regular gravel but your experience makes me think it might be worth a try. Knowing that it introduces calcium and magnesium carbonate to the soil sounds like a valuable benefit, it's certainly much cheaper than glacial dust which claims to add the same things.
I've always thought pearlite was sort of trashy looking, as I understand it provides 0 nutritional benefits to the plants aside from adding drainage. I guess it's lighter/cheaper than pumice, plus it's clean, which is probably why folks use it instead, but I love the way the fine roots grab onto the pumice and doubt they'd hold as tightly to pearlite.
Kevin,
That's cool to hear about Ed. The volcano and glacier dust claim to have trace elements though I'm not sure that their fritted. Possibly the volcano dust because I read an article that mentioned the elements becoming infused in rock during the extreme heat and pressure of it's formation, which is probably the same thing. I suppose them being encapsulated in frit/stone slows the release of the minerals, similar to a slow release fertilizer.
I haven't really determined whether the traditional semp rot we see in wet weather is from fungi or bacteria, but if it's fungi I imagine the epsom salts might help. It doesn't seem like the positive relationship that trees/other plants have with mycorrhiza exists with the more vulnerable roots of sempervivum. In bonsai it's a big plus to have mycelium growing on the roots because it breaks down nutrients in the adjacent soil which can then be absorbed by the trees, in the case of semps I think it might dissolve the roots to!
I know you want to avoid excess nitrogen to keep the growth tight in semps, and it sounds like calcium helps to, so maybe the dried milk would provide some benefit as well. Sounds like things that work for irises often work for semps to. I've had an iris potted up in one of my semp mixes for a couple years now and it's doing well so far.
Thanks for the input,
-Sol
