Paleo,
I'll be keeping my eye out for a fertilizer product that contains Thaimine but is low in nitrogen, something I could use which might toughen the plants as well as keep the tight colorful growth we love to see.
Yes I'd agree that dust of any kind should be used with discretion, especially perlite dust which probably doesn't provide any nutrients. In the case of extra fine particles, I think it's positive to have enough of them to somewhat coat your larger particles (so long as they might provide nutrients which could benefit the plants), but too many fine particles can lead to a soil more reminiscent of concrete which is difficult for roots to permeate. I bought decomposed granite to use as mulch once... big mistake! it dissolves almost entirely into fine rock dust which seals the soil with a hard shell, good for a pathway perhaps, but not as a gravel mulch around succulents.
Jesseln,
I buy most of my seed flats at grow shops which specialize in cannabis, it was at one of these shops where I first discovered mineral additives beyond lime. They do cary some wild stuff at some of those shops. I think I actually recall seeing some SEA-90, I was concerned that the semps might not appreciate it's organic compounds though (and at the time I was going out of my way to avoid products which may have contained salts), my thoughts are the same for the Mycorrhizae which I'm thinking may actually attack the slower growing, sensitive roots of sempervivum. Cannabis is much more akin to annual garden vegetables, growing ferociously for one year then dying back, all of those types of plants seem to be on the opposite side of the flora spectrum from sempervivum with regards to optimal conditions.
Anyone can plop a semp in the ground and it'll probably live, it does take some research to grow them to their full potential though. My early plantings were in the awful local clay we have here, but when my first colorful semps didn't produce or grow in the first two years I had them, I decided to look deeper into designing a soil that would suit them better, and for the most part my efforts have payed off. Aside from my recent mistake of using un-composted bark mulch in my soil, I think most of my new ingredients have lead to better growth.
Ridvan,
I thought this topic was one that hadn't really been touched on, we talk so much about soil/compost/drainage/fertilizer but never about the minerals that these plants may be starving for.
It's exciting to hear you've also had luck with dolomite, now I'll definitely have to try it. With you and Paleo both noticing positive results I'd say that definitely warrants some experimentation. Bone meal has also interested me some, combined with bio char it completes a well rounded low nitrogen fertilizer that also wouldn't be likely to attract the same microbes that might attack the semps. I am thinking about avoiding as many plant-based additives as possible these days, try to stop the rot by not giving it a reason to enter the substrate. I know Mark did some experiments with sensitive semps potted in completely inorganic substrates, don't know if he ever reported his findings though.
I often use crushed granite gravel as a mulch and quickstart during the growing season, the plants seem to like that.
Biofungicides might be something to look into as well.
Alice,
I don't think there's anything majorly wrong with pearlite, it just doesn't have nutrients to contribute and it's unsightly. Pearlite dust on the other hand sounds like a choking hazard, both for the plants and the gardener.
-Sol
