To understand what is killing it, maybe you can tell us of the decline?
Yes, for sure.
First they are healthy, with new shoots and bloom. Then, after blooming (and the flowers and stems being cut), new shoots sprout again.
Soon after, leaves start to wilt.
After wilting, they start to dry.
And then...
They die.
It goes like: thriving->healthy->good->struggling->DEAD.
In six months or so.
"A dry azalea is a dead azalea". I never stopped to think that a "wet azalea is a dead azalea" too.
My guess at the moment is exactly that: overwatering.
People here all say Azaleas like wet feet, but in my case this is causing root rot, i think.
Last one I threw out in the trashcan had all roots black and decaying.
I *think* the exact substrate is not too important. It will be in heat of the rootbal, watering regime and strength of fertilizer, I think.
I am inclined to agree.
If in the nursery soil azaleas do thrive, it's not the Kanuma that is killing them.