My experience and opinion is this: If you're not going to do a full organic grow, don't waste your time. Just pour salts through the pot, give the plant what it needs, and let it run its course. If you want to build a healthy soil web, then rock dust helps complete the symphony of particle sizes. (yes, it is often derived from clay, and/or is the net equivalent) Rock dusts seem to be most effective when used in the top few inches of the soil strata. It's useful for helping hold nutrients, more than anything, from what I see. It must be very fine, almost powdered. And it works REALLY well when combined with a complete organic fertilizer. (I like to mix with greensand and blood meal, but still use a fully built fertilizer)
My rock dust containers outperform the non-dusted containers, but I'm not suggesting that its necessarily due to direct uptake of something that is available directly from the dust, itself. And I'm not saying that it isn't, either. But for sure, it really makes a noticeable difference in the texture of the mix. (much like true soil strata) However, I would suggest that it's a long term strategy, for those with a longer growing season. Otherwise, for single season grows, I'd amend compost with it that was destined for the worm bin, and use the resulting vermicompost, in its stead. I would guess that if there's anything to be made bioavailable in any foreseeable period of time in the dust, the worms would be the most efficient means.
