Tropical waterlilies are another story. Classified as tender perennials, they will survive all but the harshest of winters in zone 9. In zone 9, it is not unusual to see tropical lily blossoms in December and sometimes January. To prepare them for winter, stop fertilizing them in mid-October. By “starving” the plants at the end of the season, they are encouraged to form small, very hard, and durable tubers. These tubers are more likely to survive winter than the large, fleshy root of the main plant. When the plant is in full dormancy (no more leaves) remove the pot from the pond and rinse the soil off the roots to collect the tubers. Air dry the tubers for 2-3 days, then rinse them thoroughly. Be sure to remove all old root fragments from the tuber (they should break off easily after air drying the tuber). Store tubers in a glass jar or clear plastic bag filled with tap water. Viable tubers will sink to the bottom. Discard those that float so they will not rot and spoil the remaining tubers that you have stored. Store the viable tubers in a cool, dark cupboard.
Plant the tubers in the pond in mid-April if you’re in San Antonio, Dallas, or Fort Worth, and early to mid-May if you’re in west Texas. They will begin to sprout new leaves in 3-4 weeks. Using a rich, fertilized soil, plant the tuber ½” inch below the soil surface, and place in a shallow area of the pond with 2-4” of water over the pot. For an earlier bloom season, you can force your tubers to sprout in February inside in an aquarium. Place the aquarium in a bright location, set the heater to 70°F, and keep the grow light on for 12-14 hours per day.
If you have a greenhouse your tropical lily can be trimmed back and placed in a small tub or temporary pool inside. At a constant temperature of at least 65°F, your lily will not go completely dormant and may continue to bloom through the winter, although not as much as during the summer. In an unheated cool greenhouse or cold frame, the lily will usually go dormant. Simply leave the pot undisturbed until new leaves come up in the spring. Once the plant is growing it can be divided if necessary and repotted in fresh, fertilized soil for the new season. This method is always successful if the temperature of the water in your greenhouse never goes below 55°F.
If you are fortunate enough to have a large natural pond, you will find that just leaving the lily in the pond is the best method. For most winters, the bottom layers of the pond retain enough warmth to protect the tubers from cold damage.
Or you can simply roll the dice and leave your tropical lily in your pond for the winter. Our winters are usually mild enough for survival. About 80 to 90% of tropical lilies survive a Gulf Coast winter with no care in 10 sq. ft or larger in-ground ponds. For added peace of mind you can also construct a “tent” of clear plastic over your pond for the winter. One group of tropical water lilies, the night bloomers, reliably survive Gulf Coast winters, even the winter of 1983 when they were subjected to temperatures in the teens for several consecutive days.
Should you lose your tropical lily to a cold winter, rejoice! Now you have the room and an excuse to try a new variety!