Pots Pots Pots!!! You'll definately lose them if immersed in water.
When potting them put some crocks/stones at the bottom to aid drainage, then fill the pots using 50% John Innes number 2 or 3 which is soil based, and 50% normal compost.
if you decide to leave them in pots, then make sure they are at least 2 feet deep and 2 feet wide. The size of the growth is relative to the amount of room you give the roots to grow in. So the larger the pot the better! and dont forget to sprinkle a handful of fertilizer in early spring like Blood and fish bone or Top rose, and don't let the compost dry out.
Best of luck Pinkpeony