Hardy water lilies grown in containers require division every year or two. Overgrown lilies in need of dividing do not bloom. They produce smaller and smaller leaves from multiple growing points in the rootstock. The lily has a congested appearance and leaf color may be yellowish. The lily's container may be so full of roots that it is difficult to insert the fertilizer tablets.
Division and repotting usually restores vigor and bloom. The best time to divide a hardy water lily is in the spring although they may be divided at other times of the growing season. After repotting, a lily usually does not bloom for three to four weeks.