Sacha wrote:

That's not compost though. *That's soil improver, if that.

And highly variable too :-| I've seen some that is OK, but I've also
seen other stuff that is truly 'crap' and not fit for anything. As
for growing on plants in containers, if you aren't particular about
the quality of what you're growing then go for the cheapest potting
compost you can find. If you want to grow a really good plant that
performs well and makes the effort of growing it worthwhile, then you
need to either make a well-balanced compost or buy a decent one. The
latter is the least expensive and easiest option.

All multi-purpose composts 'run out of steam' after 6-8 weeks, so they
need to be supplemented after that, but reluctantly I have to admit
that the best all rounder is the B&Q multi-purpose. It has beat the
others in trials by Garden Which? for 2 years running and I like its
open, airy, root-promoting texture. I use it as a base, adding
perlite and slow release for certain plants and use it 'neat' for
others. I've never had anything other than very good results.