All I can say is they grow very well in my south facing front garden which gets very dry. I have found though anything I have bought from anywhere other than a garden centre never seems to be very good.
Tilly, be careful with what you buy - I've seen the ones in Aldi (which are no doubt similar to Lidl) and some of them are definitely artificially coloured, so the colour won't last. The only ones which are authenic are the white, pale pink and purple (which are heather's natural colours).