Hardy Water Lilies
Once winter approaches and the water temperature of the pond drops, the hardy lilies automatically go dormant. If any new leaves appear, they will be very small and will remain under the water, close to the soil. As the old foliage browns, simply prune and lower the lily to the deepest part of the pond. If a sufficient depth of water can be maintained so that freezing does not occur at the root level, the hardy lily does not need to be removed from the pond.
If there is a possibility of the pond freezing solid, there are several methods of protecting the lilies. If you prefer to leave the lilies in the pond, place boards, side by side, across the top of the pond. Cover the boards with mats or layers of straw or leaves, weighted down with stones. In the spring, as the ice thaws, all the covering must be removed to prevent premature growth.
For indoor storage until spring, a cool basement or heated garage are possible choices. The lily tuber should be covered with moist burlap, peat moss or leaves. You could also cover the soil with newspaper and place the entire container in a sealed plastic bag. Check occasionally that the soil is moist.
Tropical Water Lilies
Tropical lillies are most often treated as an annual. They continue to grow and bloom until several freezes drive them into dormancy.
If you choose to store your lilies through the winter, a greenhouse is the most successful way. Provide only 10-20% of the space of your pond. A wash tub or tank is suggested. The lily should be kept small, so don’t fertilize.
Another method is to use an aquarium. Pot the lily in a 4-6″ pot, plug holes, and place in at least a twenty gallon tank. Heat the water to 70-75 degrees F and place a fluorescent grow light close to the top of the tank. Do not encourage growth. Simply keep the plant alive.
Some specialists consider starving plants in late summer, causing the formation of tubers. Once all the leaves are dead, feel under the crown for a hard tuber. Remove the tuber and wash it thoroughly. The smaller tubers generally make the nicest plants the next spring. If there’s any root or stem tissue still attached to the tuber, air-dry a few days then snap it off cleanly. Again, wash the tuber well and place it in a plastic bag or mason jar. Fill the container with distilled water or slightly moist sand and store it in a cool, dark place at approximately 50-65 degrees F. Be sure to check the container regularly. If the water is foul or discolored, replace it with fresh distilled water.
A tropical lily should only be placed in water of 70 degrees F. Do not rush the plant outside. It could return to dormancy or it may die.