The next picture is 'Shima Nishiki', a bright red double. Most of our red tree peonies have a magenta cast to the color, but not this one. It is definitely red.
'Mystery' is a pale pink on with darker shading towards the center of the petals. It always seems to have this odd shape, seeming to be not quite open.
Last picture this morning is 'Black Douglas', the darkest one we grow, and maybe the darkest one out there. I've seen blooms that were even quite a bit darker than this one. It is very double and will open a bit more than in this pictures, but will still seems totally packed with petals.
When we first started growing tree peonies, the accepted wisdom was that they had to be grown in the shade and so our tree peony beds get quite a bit of shade. A half day at least of sun is now recommended. Morning sun is better because it fades the blooms less.
Tree peonies can be planted bare root any time in the fall up until when the ground freezes. We do most of our planting in October or early November, but have been known to be working in temperatures that just about froze our hands. If you buy a potted tree peony, you can plant it any time during the spring, summer or fall. As with any plant, dig a generous hole and loosen the edges. Incorporate some good compost in the hole if possible. After planting, mulch your new babies well. Remember, when planting tree peonies that they are grafted and you need to have the union of the top and root at least 6 inches below ground level. A lot of nurseries will put a marker at that point to make it easy. If you don't, the rootstock will send up shoots and take over, killing your tree peony. If you see herbaceous shoots appearing, remove them. What will happen over a few years is that the tree peony 'top' will grow its own roots and no longer need the root part. Tree peonies are grafted for propagation because they just don't multiply fast enough. You can divide an older tree peony and have a new on that will be on its own roots. If you do divide a peony, tree or herbaceous, don't expect bloom right away again since they take awhile to adjust.
No pruning is necessary except to remove a dead branch. These are wonderfully self sufficient plants. Yearly fertilization is recommended with something low in nitrogen but rather high in phosphoris and potash. We no longer use commercial fertilizers on ours, but rather mulch heavily and use compost. Our plants seem to like it.
In far northern areas they may need some winter protection, but we've never needed any here in zone 6.
Very few things bother tree peonies. Deer don't eat them and rabbits only occasionally will nip a new shoot. Botrytis is the only disease we've ever had any problem with and good air circulation is the best preventive for that. Captan or Benlate will cure it.
I'll write a little bit on growing tree peonies from seed tomorrow and then it will be on to the herbaceous ones.