There is more than one type of fern leaf. There are true species P.tenuifolia and P.tenuifolia 'Flore Plena'. I have one of the species singles and a species double on order. The one pictured came from Spring Hill nursery a few years ago. It was sold as a double but turned out to be a single. I have divided and moved it 2 or 3 times. This is the third year in its present spot. I do not think it is the true species type due to the root structure so it could be one of the many hybrids. The species fern leafs multiply very slowly so do not expect them to spread like the common peonies. My double red is a hand-me-down from my wife's grandmother. We have had it for 30 years but it was planted close to a tree and did not do well until I moved it into the sunlight. It too has been divided at least 3 times and I now have 3 very healthy clumps about 3 years old.
They require full sun, prefer reasonably deep very well drained soil, and very little watering in a normal climate. No watering after they go dormant in late summer or early fall. I think they originated in very harsh climates so too much tlc does more harm than good.
There is a lady in Canada who has a huge clump of the single type but I do not know how long she had it. It appeared to be 4 or 5 feet in diameter in the picture she posted a couple of years ago.
