Overwintering
Tropical Water Lilies
By Rich Sacher, New Orleans, Louisiana
Tropical water lilies are perennial by nature, arid they will go dormant as the weather becomes cold and days grow shorter. In New Orleans, they will often bloom until mid to late December, at which time the plants are already becoming smaller and slow-growing.
You should stop fertilizing the lilies in mid-October, because by starving the plants at the end of the season; they are more likely to form some small, very hard and durable tubers which survive the dormancy period much better than the large fleshy root of the main plant. These small tubers can be broken off from the parent plant and rinsed clean of soil; they should be stored in damp sand for the winter at a temperature of 50 to 55 degrees. These tubers can be planted out in the pond in mid-April, where they will begin to sprout new leaves by the middle of May. (Plant them in rich or fertilized soil, one half inch below the sod surface, and place in shallow area of the pond with 2 to 4 inches of water over the pot.)
If you have a greenhouse, you should move your water lily to a small tub or temporary pond inside. In this case, do not disturb the roots; allow the plant to continue growing until it becomes dormant and leave it in the pond until new leaves come up again in spring. Once the plant is growing again, it can be divided if necessary and repotted in fresh soil for the growing season. This method almost always ensures the survival of the plant if the temperature never goes below 55 degrees in your greenhouse.
Those people who are fortunate enough to have a large natural pond will find that just leaving the lily in the pond through the winter is the best method; this is especially true if the pond is fed by artesian well where the water temperature of the pond stays above 50 degrees no matter how cold the winter nights might be. This allows the plant to go dormant but the temperature is warm enough to prevent damage to the tubers. If the water temperture of your pond goes below 45 degrees for a number of days during the winter, then you will need to move the plant or tubers indoors for the dormant season, because temperatures below 50 degrees may result in the death of the tubers.
Since winters in New Orleans are so unpredictable, I would guess that most people would have about a 50% success rate if they just left their lilies in their ponds through the winter. Because the winter of 88-89 was so mild, the success rate for overwintering lilies was more like 90%, according to most pond lovers in this area. The determining factor is temperature; how cold does it get and how long does it stay cold.
SO, if you enjoy a challenge, try one of these methods of overwintering your lilies. Or, if you want to be more laid back about it, you can do nothing at all and take a chance on Mother Nature. You should win about half the time!