If you mean digging them up and putting into pots I wouldnt as they hate being moved.

They have a large tap root system that does not like being disturbed. I think that pot culture would be difficult.

Thanks for you answers but i think i gave you the wrong idea. I have bought the paeonias and as we have little garden i thought about putting them in lardge pots. they are 3 year plants and have come to me as dry roots ready to be planted. If i put them in pots how do i care for them? answers asp as i need to plant them this weekend

Liam, I really don't know how to give a reasoned answere to your query as container cultivation of tree paeonies is not something that I would do. I would suggest a rich, peat free compost with plenty of grit added to it for drainage. Keep the pot itself in a cool, shady position to stop it getting hot but allow the stem and foliage to get plenty of light.
Good luck

Liam I think you are going to have a problem trying to grow tree peonies in any sort of container... their tap root goes down for well over a foot as they grow and they need this to anchor them. A peony is fully herbaceous but a tree peony grows on from the previous years growth so they can get seriously large. Bulbaholic and I recently pruned back our tree peonies a little before they came into leaf... at that point the branches were well over 5 foot in length. Plant them in the ground or accept that they are not for your garden.