A sad Paeonia Sorbet

Well, it could be a number of things, kazza, some varieties don't like travelling and will sulk on being placed in a new pot. One of the golden rules is not to plant them too deeply, an inch of two of compost/soil over the roots at the most. I would keep it in light shade for the moment and keep the compost/soil moist. They're pretty tough plants and yours should settle down and recover after a week or too........or not
Can I ask if you intend to keep them in the pots? I'm not in favour of keeping such large clump growing plants in containers as they just don't seem to perform as beautifully as they do in the ground. Despite all the myths you hear about established Peonies not liking being divided and/or moved my Wife used to regularly move our Peonies when she wasn't happy with anyone and we had no problems. Again, when planting into a border, just cover the roots with just an inch or two at the most.
So if you bought the Peonies bare root it doesn't matter who the supplier is, bare root peonies have got to start afresh so they will take time to establish themselves, especially in a pot. They will probably take two to three years to produce flowers...........but it's well worth the wait.

 

If you don't try, you'll never know, kazza. Peonies will grow, naturally, into clumps of 4' to 6' wide depending on where they are, in a pot they will be very restricted and will need feeding regularly but even so will never compare to that of a Peonie in the ground which will give around 40 to 60 flowers in a large clump of say 6 years
I tend to break all the rules and advice of the book selling "experts" so I'm the last person who should be telling some one not to do something So keep them moist, and then after about 6 weeks give them a feed of Tomato Feed and they will settle down. I now have around 11 different varieties of Peonies, with ages ranging from 30 years to around 3 years and can't resist roaming from each one and filling my lungs with their scents. Let us all know how you get on!!

 

Ordinary compost general has enough nutrients in it to last around 6 weeks,kazza. So I would let the Peonie settle into the container for a while. If it is a bare root it will spend some time putting down roots to build itself up. Yes, it will grow "OK", but restricted, in that compost and pot, but I would not expect flowers for maybe 3 years. I did suggest using Tomato Feed but,taking into consideration that it is a bare root plant having to establish itself, I would withdraw that suggestion and would give it regular feeds of, say, Growmore.