Hardy water lilies grow as far north as Alaska and over-winter easily in Denver and other Colorado locations. In nature, these plants lose their leaves in the fall. The root system, or rhizome, remains alive providing the basics for next year’s plant.
In October or November, hardy water lilies can be lowered to the deepest part of a pool. Plants can also be moved to a root cellar or garage where winter temperatures fall to near 40 degrees Fahrenheit.
Hardy water lilies benefit from a long, cold, winter rest period, but don’t let the rhizomes freeze or dry out. Growth resumes in April.
Most tropical water lily species are found in Africa, and, thus, need a different winter treatment than the hardy water lilies.
In October, prior to our first frost, remove plants from their large planting containers. Most leaves and roots can be trimmed and the plant repotted in a one gallon pot. After repotting, move the plant inside to an aquarium tank or some other container. Be sure to provide plenty of light and keep the temperature above 68 degrees Fahrenheit.
Some tropical water lilies produce acorn-size tubers at the base of the crowns in late summer or fall. These tubers can be removed and stored in water at 55 to 60 degrees Fahrenheit for the winter. They sprout in the spring when placed in 70 to 75 degree Fahrenheit water in the greenhouse. Initially, they should be planted in three-inch pots, and moved to five-inch pots later.