I am getting conflicting information about how safe vermiculite is. Some think it's safe enough that some people even mix the soil with bare hands. Some say that you have to mix the soil outdoor with face mask. How safe is vermiculite if I am using it for indoor plants?
It's only harmful if you inhale it. Touching it with your hands won't hurt you, as far as I know. The danger is that some sources of vermiculite, most famously a deposit near Libby, Montana, contain asbestos impurities. There's also the simple fact that it's usually not a good thing to inhale small particles of anything, whether it's going to give you cancer or not, but that's a smaller worry. I suspect the reason for the conflicting information out there is because people can mean different things by "vermiculite" (where is it from? how pure is it?) and "safe" (will it knock me dead immediately? will it give me cancer in 50 years?). Personally, I don't think it's enough of a risk to concern myself with: I don't use it very often, it's generally wet when I do use it (the dust gets into the air easier when it's dry), I'm using relatively small quantities, and I'm hoping that there's some regulatory agency somewhere checking the vermiculite that gets sold to ensure that it doesn't contain asbestos. (That last one is maybe optimistic of me.) If you're not using huge amounts, or using small amounts daily (as for example if you were handling it occupationally) you probably don't have a lot to worry about from vermiculite. That said, it doesn't hurt anything to try to mix your soil outdoors (for the ventilation), or to wear a mask or respirator when you're dealing with it, and to be careful how you dispose of used soil if your soil mix contains a lot of vermiculite. It's not likely to make a difference either way, but you may as well.
Thanks for a dose of confidence. I think I need the vermiculite for my african violets because just perlite alone doesn't seem to have enough aeration. I think that's because my place is air tight especially during winter when we have to close the windows all day. Since they are going to be placed next to couch and in bedroom, I am going to experiment mixing perlite and vermiculite for bottom two-third part and just perlite for the top layer.
Soil aeration will not affect unsuitable atmosphere - that is two different things. My understanding is that vermiculite, being a sort of flat wafer, does not provide as much aeration as perlite or pumice.
It didn't occur to me until someone teaches growing african violets at AV Society pointed out to me... I used to live in an apartment where windows have broken seals so there are draft. However, my african violets bloom beautifully without any care at all. Friends thought they were fake flowers. My current place don't have window problem but AV are not doing as well and the soil seem tight. I tried various ways of watering, locations, brands of soil, etc. but soil still seem tight to me. I studied the soil used in the AV exhibits and many have golden mica like substance. I was told they are vermiculite. Several websites recommend using combination of perlite and vermiculite so I decide to try this out.
The reason that you see vermiculite used very frequently in seedling mixes, but rarely in potting soil, is that it compacts faster that other comparable ingredients. It does provide excellent short-term aeration though, which matches perfectly with the needs of seed or cutting mixes. I use a combination of equal parts perlite & pumice, added to my standard recipe potting soil to get as much extra drainage as I need. The perlite is a little better at aeration, but the pumice is good too, and its slightly heavier weight solves the problem of too much perlite floating up to the top.
