By Barbarak
North Yorkshire,
United Kingdom 
Tree peony. I bought a small specimen last year at this time and planted it in a large 30cm square container. After reading more about how temperamental they are I have a place in a sunny border for it. What would be the best time to move it into the garden? no flowers this year but didn't really expect any.
18 Aug, 2017
Answers
So leave it until the leaves fall and plant it dormant.
18 Aug, 2017
as its in a pot it can be planted any time really. dormant will cause less 'shock'. I planted mine from a pot into the ground in June. needed lots of watering but it is doing fine.
18 Aug, 2017
Yes growing in a sunny position should work for your tree peony, which is actually a deciduous shrub. Copy and paste the link below for all the RHS into on these and how to grow:
https://www.rhs.org.uk/advice/profile?pid=711
18 Aug, 2017