Hi, 1st time user of this site. I would like to know what to do with an out of control purple berberis bush (tree). I chop it back about twice a year to show it who's boss but I'm really not sure when I should do this and how much could I get away with so it would be about 5 - 6 ft in the summer. I would like to do this only once a year.

Any advice appreciated. Thanks, James