Mark my only advice is and only the obvious is drainage, watering unfortunately is a feel thing, but if your still keen and your more than probably doing it, is to latch onto a dedicated azalea grower in your area, get his medium mix and stick to his mix and keep listening to him/her and as for killing trees.. mate I have killed more trees than you have in your collection and some, so don t worry about that as long they last a little bit longer each time and you are learning haha...so get some more and keep going, don t let them beat you Mark

cheers Anthony