Hi

I wonder if anyone would be kind enough to explain what the main differences are between the black soil like John Innes formulas and the "multi-compost" type which is lighter in colour and springier?

Perhaps more specifically, I have a small Leylandii screen on a balcony in 10 inch pots which I'm planning to move to 12inch ones that are currently in the multi-purpose compost. Would they be better off in the black John Innes soil ? And in general when to use soil like John Innes and when to use the compost stuff?

I've been searching around the internet for hours but haven't really found an answer to this - maybe its so simple nobody feel the need to explain!

Thanks in advance for any advice on this.