Posted: 07/04/2013 at 13:28
I did some research into this and no-one seems to know the answer. Except that , it is reported that the best mulch for Rhododendrons is...................Rhododendrons. The reason ,apparently, why these plants are unhappy in Alakline soil (limey) is that the lime locls up Manganese which they need. The old leaves contain Manganese.
However, they also may be vectors in passing on a nasty disease which is killing off swathes of them, so all in all I would not take the risk myself.