It’s one small upside to fall yard cleanup: All those perennials you’ve been nursing ... and your hori hori is your best tool. Use it like a knife to cut through the rhizome.
When to Divide Perennial Plants: Generally, fall's the best time to divide perennial plants that bloom in spring and summer. (Conversely, spring's the best time to divide fall-blooming plants.) But if ...
Many perennial plants benefit from being divided every three to five years to improve plant performance. In general, spring and early-summer blooming plants are the best candidates for fall division.