Is it in a pot or in the ground? How long have you had it?

I have also got a yellowing, dropping leaf problem. Mine are in 2 large half barrels growing as mini standards. I've assumed it was the cold winter. How can I rescue them?

Rozalia, it may well be they need potting up into something larger - check how rootbound they are. This is what I was thinking for this questoin, and why I asked whether they were in containers or not.