It will only grow as big as the roots will let it. It might need some fresh compost this spring - if you can't tackle getting it out of the pot and shaking off as much compost as you can then repotting, you can scrape as much compost as you can from the top of the pot and replace it with some fresh. John Innes No 3 is best for plants that are going to stay in their pot for a good long while.
It's a lovely shrub with great autumn colour and I want to get one for the garden we're creating here in our new home 
