Water lilies are tuberous plants with tubers that grow roughly vertically with fibrous roots beneath. Hardy varieties can be plant out in the pond from late spring to late summer, so they will have enough time to establish before winter. The tender, tropical varieties can be plant out only after the risk of frost have passed, or just grow them in a conservatory pool. If grown outside, they need to be lift and their tubers stored over the winter in a place with 5-7 degrees Celsius (41-45 F), in moist sand and protected from rodents.
Use 30-35 cm diameter and 15-19 cm deep containers for planting water lilies. Trim long roots and cut off any damaged leaves and flower buds before planting. Plant them, add a sachet of slow-release fertilizer and water well so the container will be heavy enough. Lower the container into place. Repeat feeding with slow-release fertilizer every six weeks during the growing season.
To keep them in good shape, they need to be divided when their foliage is crowding the water surface or when the roots have outgrown their container. Lift them, cut off pieces from the crown making sure each is having a young and strong shoot. Each piece must have about 15 cm of attached tuber. Replant the pieces in fresh soil and discard the old crown.
Propagation of water lilies can be done by bud cuttings, division of rootstocks from rhizomatous types, plantlets separation or even by sowing seeds.