I've managed to find a local nursery to supply all my plants at once for those of you who saw/commented on my thread yesterday (and thankfully I did not refer to perineals in my email to them 
).
I have a quick question about planting so I can confirm plant numbers.
I am aiming for a overgrown/intermingled look. How much do I take account of the eventual spread of the plant I'm putting into the ground? I don't want it to look too sparse (I realise it will initially) but do want the plants the reach their potential.
For example one of the plants I'm using (Perovskia blue spire) will eventually grow to a 1m spread but plan to mix this with a couple of other shorter plants in a 1m square space. Is this what I should be aiming for?
I suspect I'm making this more complicated than needs be but am on a steep learning curve here.