Tree peonies are an established popular plant here, growing well, and nothing handsomer when in bloom. However, my history of buying and growing them is complicated. It used to be possible to purchase potted plants in the local nurseries, to grow on in pots or plant out; and they grew. These were named varieties, though they came without names; they were fairly costly for local-nursery-potted-plants, but worth it. Then things changed. Potted plants I bought didn't survive, however cosseted: they had apparently been grown in the ground, then lifted, their roots reduced to near-zero to fit them in the pots, where they were dumped with compost and put out for sale (wholesale growers, retail nurseries). They died.
Alternatives? Pay a decent, i.e. high, price for plants correctly grown and prepared for sale. I don't willingly spend that much money. Propagate my own? From what I read, tree peonies are hard to impossible to propagate from cuttings; they don't sucker, or not much, so, no plants that way. Most commercially available plants are grafted onto herbaceous peonies, I seem to remember, and I've never practiced grafting. Last possibility, try to grow them from seed, and see what happened.
I did this once, some years ago, collecting tree and herbaceous peony seeds and attempting to grow them in pots. It was a near-total failure, but I did end up with one tree peony (plus a few herbaceous ones). The parentage of this plant was obvious, as it looked very like one of the ones I collected seed from, only more pink in hue and less lavender. It's a lovely plant, eminently worth growing. Unfortunately I left it too long in the propagation beds and it has become a permanent resident, as I'm also terrified at the thought of trying to move a tree peony.
So last I year I once again collected tree peony seeds, from the lavender one as before, and its handsome offspring, and put them in plastic produce crates lined with several layers of newspaper and filled with compost. I waited. The cats used the trays as litter boxes. I swore, and covered the seedling flats with further plastic crates, ones that let sun and rain through, and weighed them down with wood to keep everything in place. Nothing happened. I had read, and it has been my experience, that peony seeds collected fresh will sprout quickly, while ones gathered later can take a long time to germinate. I thought I had collected these promptly, but swallowed my impatience and left the flats to go on. The winter passed.
Finally, yesterday, I was checking the pot ghetto, and there was a tiny little peony shoot! And another, rather battered. Another check today showed a third one. So, they're on their way, though not safe yet with enemies like snails around, and the plants so little and fragile. What a rewarding sight, though. Who knows, I may yet fill the garden with home-grown tree peonies along with all the other wonders. Gardeners are hopeful sorts.
My 'Mollis' peony, a Mediterranean peony, seeds readily, and the infant seedlings survive, in spite of terrible soil and drought, and grow. I started many years ago with two plants and am now up to about twenty, most of them tiny. This fall I want to shift a couple further out in their bed and spread the effect. They're a nice peony, but the thrill of their seeding adds considerably to their interest and charm. I'm also wondering about various forms of P. officinalis, and P. peregrina, found further south in Italy, and whether they could set seed. P. peregrina has never done so: is it because it's a single clone? There are two clones readily available in commerce: what if I bought both, and planted them together? Thoughts and schemes for the future.
P.S. If other peony fans and students read this and notice faults in my information, by all means point them out! I'd love a discussion on growing peonies, even if it's here on the old roses forum.
rosaprimula UK (Cambridge) Z8/9