I would treat it like an additive as Irina says. I would thoroughly mix it in the soil like any other additive. As far as the ratio, got no clue on that. Rosie

My thought is that it is less value as a straight fertilizer but more of a source of the microelements and beneficial soil bacteria. Too much of it - and then you need to consider it a fertilizer - and adjust your fertilizing routine to avoid an overload.

Exactly my thought too! Thank you both :o)

I put it into my mix when I make it up for repotting. You would only spread it over the surface if you were adding it to plants that are already potted and not due for a repot, IMO. I agree with Irina and use it lightly as an additive.