I went to Stoneleigh park for 'edible garden show' and the rockdust dust people there told me about the B&Q going to do it. I did buy 2 big sacks of the stuff then, but I've already used one and second one is open too so I shall need re stocking again soon.
I don't think there is anything wrong witht he fertility of my soil ...but it doesn't hurt neither to give some of this stuff neither. I haven't used it for several years, last time I did, it eventually did make noticeable difference. And the apple tree that stands on the spot where I had rockdust 'accident'..and loooots ended up into ground..well that tree just goes bonkers with fruit without fail. Tree 'next' to it doesn't do half as well.
I'm totally converted to use it now..not every year for same areas but here and there every other year.. ;)..though I'm still trialling with the results.
