Lee others know lots more than I on water lillies, but here you go. I have seen them climb out of pots several times. The pondowner then spend conseiderable money paying me to kill them. However I think if you monitor them in the pots this can work, and is much better than planting. Of course the lilly experts will direct you to varities that are not as invasive and can not tolerate as deep of water.

Greg Grimes
www.lakework.com