This is a beautiful bush in my garden that flowers most of the year with the mauve flowers you see in the photo. There are still a couple left and picture 2 shows them..unflowering. Butterflies love it as do bees in particular. I need to trim it back but I note that its is fairly bare in the center with most of the leaves /flowers on the fringes. Firstly I need to identify the bush and secondly any tips on how aggressive I can be in cutting it back would be much appreciated.