This plant likes acid, moist but free draining soil conditions - do you have it planted in full sun in alkaline conditions, or somewhere too dry for it?

Thanks very much for your answer. I have planted my tree in acid compost in a pot which is placed out of the sun under a pergola in my garden. I presume from your answer that it would appear my tree is becoming too dry therefore I must remember to water it.

Also consider how long its been in the pot - if its been there more than a year or two, it might need potting on.