I have 5 hardy lilies just in the rock, they probably don't bloom as much, because I don't fertilize them. My pond guy said they filter the water better when not in pots and the fish provide nutrients. It must work because that lily wasn't there last year. I grow them mostly for the cover the pads provide and the lilies are a beautiful bonus. I do have some large buds coming up right now.
He installed four when he built the pond and I hope to post some pictures when they open so maybe you experts can tell me what they are.