Posted: 28/02/2014 at 10:30
I'd re pot into something bigger in spring, prune back a bit and give it a feed. The more top growth you have, the bigger the rootball needs to be to support it, so it's probably a bit pot bound in the one it's in. Tease the roots out a bit when you re pot - if they look like they're just going round and round in circles that's the sign they're potbound. Anything that's permanently in a pot needs a bit more looking after in terms of water and nutrition, especially a large shrub.
Each spring take some of the compost out and replace with new to keep it happy, and just check that drainage holes aren't blocked so that it doesn't get waterlogged either.