I think these are fab and was going to buy one the other day, but I'd not done all my research, so didn't bother as it was quite expense.
I think your right to apply a balanced feed, they do like their food. There are also a bit tender in coldish climates and can at times loose leaves and turn yellow, if exposed, so perfectly normal.
Something to consider - Have you checked the root ball, you say you bought it last year. Gently check to see if it has took, is there plenty of new roots for example or, is the ground to wet, they do like plenty of drainage. They can be susceptile to Phytophthora root rot.
Symtoms of Phytophthora root rot above ground are wilting, yellow or sparse foliage and branch dieback. Below ground, poor root system.