Re: shearing perenials
In the past I have given post-bloom haircuts, but not cut back all the way, to C. verticillata. Nepeta ‘Walkers Low’ has always responded wonderfully to a post-flowering hard cut back, getting rid of the floppy stems and reblooming again to a lesser degree later in the season. I normally cut my Phlox back by about 1/3 by the first week in June. Smaller less robust plants are given a small pinch or left alone. Monster phloxes outgrowing their space get chopped even harder. They love it!