Sisyrinchium bellum (Blue Eyed Grass)

Good afternoon every one friend gave me some cuttings of blue eyed grass a few years ago. They had know idea what the plant was called. I planted the cuttings which all had roots and forgot about them. The following year the grew into four different clumps.  I left them alone for another two years until last year. I dug up all clumps and thinned out and replanted and this year was given a beautiful display of brilliant white dainty flowers. I have managed to edge the the flower bed with this.
The flowering seems have slowed down now and I would love advice on how to care for the plant I know it seems to be hardy, and perennial. Can it be trimmed.
Look forward to your replies