I know what you're thinking. There's nothing to it! They easily and happily return each year.
What you may not know, however, is that if there were a group for Aggressive Weeder's Anonymous, I would join. No intervention would be required. I know I weed a little too aggressively.
I have weeded out all my echinacea, and have had to buy more. :(
I have weeded out all my coreopsis, and have had to buy more. :(
Whenever a perennial plant doesn't return, I wonder if I have weeded it out. (Of course, I have also weeded out a lot of weeds!)
This year, I tried very hard to leave a few plants that looked suspiciously like weeds to me, in the hope that they weren't actually weeds. Well, it paid off! Some of those weed-look-alikes were, in fact, coreopsis. My quest for finding coreopsis the second year was finally successful!
Look at all the sweet, sunny, yellow blooms! Coreopsis! Proof positive that I am becoming rehabilitated. Let the quest for echinacea begin!