Tropical water lilies can survive safely outside only in the mildest climates such as Zone 9 or the southern part of Zone 8. Even then you take the risk of losing them if you have a colder than average winter. The vast majority of the country will need to treat them as annuals or overwinter them inside in a protected environment.

My preferred method of overwintering tropical water lilies is to force them into dormancy so they will make a tuber. About six weeks before freezing weather, stop fertilizing your tropicals. The leaves will become smaller and smaller with the help of the first few cool fronts of the year, the plant will go dormant and produce a tuber. Tubers will range from pea size to the size of a golf ball generally being round or elliptical in shape. Medium sized tubers tend to survive the best, discard any tubers that are soft or mushy. Remove your tuber from the pot and wash off any soil. If the tuber still has any roots remaining I like to float them outside in a bucket of water until the roots rot away or are easily removed without damaging the tuber.

Tubers can be stored several ways. I like to place them in Tupperware containers or plastic bags with LIGHTLY DAMP, coarse sand. The key here is that the sand cannot be too damp, just moist enough to stick together. Make sure no tubers are touching one another in your container as this could spread mold. Store your tubers in a cool dark place with temperatures between 50 to 60°F.

When spring arrives pull your tubers out and place them in a heated aquarium at 75 to 80° F. The tubers, if they are viable, should sprout within 7 to 14 days. If they do not sprout and are still firm, place them back in the damp sand for a couple of weeks. Sometimes this second dry period will help tubers break dormancy.

When water temperatures in your pond are above 70 to 75°F, pot your tropicals up and place them in the shallow end of the pond, or on cinder blocks. These young plants are very tender and if the temperature drops you may need to bring them in for a brief period until the water warms up.