Koi-lo's considerations aside some species can become huge it allowed to run riot. The up side is you stand a chance of a stunning display of pads and blooms. One chap I know has free lilies and he is 600 or so ft higher mean which generally means his plant should be behind mine. I seem to remember him having 20 blooms on one large plant before I even had pads on any of mine. I have several pygmies growing loose in a gravel bed in my fish pond.