I tend to see black leaves on them due to lack of water/too much sun. They do best in moist soil in semi-shade - badly in dry soil and full sun. I wish my one would do better - it has semi shade but Vine Weevils and Slugs get to it.

I often get black leaves on my Aucuba bushes but I just prune them out and they survive and soon grow back. Mine are all in shade and as Kildermorie says they seem to suffer when we have dry spells.