goldenrod is one of those perennials which if some stems are shortened in late spring/ early summer can have its flowering season extended the shortened stems flowering later than those un-touched....there was big publicity thing about this when some american gardening goddess brought out a book earlier this year detailing her experiments and what worked and what did nt....she did nt invent the process though...a few years ago my nephew threw his frisbee around a border in early summer with interesting subsequent results.