Overwintering Hardy Water Lilies and Lotuses
Techniques for plants grown in tubs or pools
Many water plants will survive the winter in a pond or pool. However, plants in raised tubs, pools and other vessels will not survive the winter if you routinely have long periods of temperatures below freezing.
To try this technique, you will need a place to store the dormant plants. Temperatures should range from 30 to 50 degrees F. Light is not necessary because the plants will be dormant. An unheated basement is ideal, but you can sometimes find these conditions in garages or sheds, too.
Note that this technique is only effective with "hardy" water lilies and lotuses. In other words, they must be plants that normally spend the winter in dormancy. Tropical water lilies are generally treated as annuals.
Once temperatures have dropped in the fall, find a bucket or tub that's large enough to accommodate the pot that your lily or lotus is planted in. Take the plant from your outdoor garden-pot and all-and place it in the winter storage bucket. Remove all dead and dying foliage. Move it to the place it will spend the winter, and fill the bucket with water, covering the surface of the plant's soil by about 2 to 6 inches.
During the winter, check the water level occasionally to make sure it's still covering the soil surface by a few inches. Once the weather has warmed in spring, you can return the lily or lotus to its summer home.