When we moved to our house eight years ago, I found several peony bushes planted by the shady west wall. They bloomed abundantly in the spring, but their huge pink flowers had no smell:
I couldn't believe that someone would plant scent-free peonies, but took consolation in the fact that they were also ant-free.
A few years later I made a flower bed by the stone wall in front of the house, and needed big plants that would look good all season long, even when they weren't blooming. I like the looks of a peony bush, flowers or no flowers, so I walked around to the shady spot where the pink peonies lived and transplanted six or seven of them to the new bed.
The bushes rooted well, died down to the ground in the winter, and sprang to life the next spring. Soon they were covered in buds, but when the flowers opened one sunny morning, they were almost pure white...and they gave off clouds of that unmistakable, that divine, peony smell.
Every year since then the peonies have put on their show: pink and unscented and ant-free on the shady west side, white and perfumed and beloved of ants in the sunny spot.
How can this be? I can imagine that a change in soil composition might cause the change in color, as hydrangea aficionados know. And perhaps the sun exposure has something to do with it. But the truly miraculous part, the scent that would cause me to plant peonies even if they looked like crab grass, remains a mystery.
If any of you botanists, peony-loving gardeners, or lyric poets out there have a theory, I'd like to hear from you.