Hardy, northern water plants can withstand a freeze and survive the winter and only require a little maintenance to prevent the buildup of rotting debris on the pond floor. Winter water plants are adapted to the water conditions of their native climates. Tropical plants are not frost hardy and require far more care if they are to overwinter successfully.
Remove all tropical water plants with the exception of water lilies and marginal plants from your pond after the first freeze or when the plants begin to brown. Most tropical aquatic plants are difficult to care for over winter, and it is usually cheaper and more convenient to treat them as annuals.
Remove tropical water lilies after the second freeze forces them into dormancy. Fill a child's pool, tub or fish tank with water. Dig lilies up and plant them in pots. Submerge the pots in the water in a greenhouse. The cool temperature should keep the plants dormant all winter.
Cut the stems of hardy marginal plants to 6 inches long. Place the plants near the deepest part of the pond.
Trim tropical marginal plants to 2 inches tall and bring them indoors in pots in late fall before the first frost. Drape wet burlap over the pots and store them somewhere cool and dark, such as a basement. Check every week or two to make sure the soil under the burlap stays moist.
Prune hardy water lilies in fall to remove any brown parts of the leaf. Move them to the deepest area of the pond.