One of the best-selling garden books of all time introduced us to the notion of pruning perennials. The book is The Well-Tended Perennial Garden by Tracy diSabato-Aust, published in 1998. Among many other bits of great advice, the author advises boldly hacking back perennials early in the season - now - in order to create shorter, fuller plants that won't flop over when they reach their full size.
In my garden, the tall perennials get their first haircut in early May, and it's generally recommended that even the latest-blooming perennials have their last haircut by the end of June. I play it safe and do it as early as possible, as long as the stems are at least a foot tall. I simply cut off the top half of each stem.
Here are the plants I've hacked back to good effect in the past and will continue to prune that way:
- Asters of all types because boy, can they flop! Especially when they're in a bit too much shade.
- Tall Sedums, like 'Autumn Joy'. Ditto the problem of shade causing flopping.
- Garden phlox.
- Echinacea purpurea (Purple coneflower).