Q. Will my water lilies overwinter outdoors? If not, is there anything that I can do to keep them over the winter?
A. Your water lilies' ability to survive the winter outdoors depends on whether the plants are hardy or tropical. Hardy water lilies rated cold-hardy for zone 5 will survive winter temperatures in the Chicago area for years, providing the rhizomes will not freeze during the winter.
Tropical water lilies are zoned for warmer climates and will not survive Chicago winters. In order to keep them year after year, remove them from your pond or aquatic container before the first frost in the fall. Place the potted plants in containers or plastic bags and store them in a cool, dark area indoors that remains above freezing such as a crawl space, basement, or closet. Monitor the plants during the winter months to make sure that the plants are always damp; do not allow them to dry out. The water lilies can be re-acclimated to the outdoors after all danger of frost has passed and the water temperature remains consistently around 70 degrees.
Tropical waterlilies must be removed from the pond four to five weeks before the Chicago area’s average frost date of October 15. Cut off any flowers, stalks and foliage and store the tubers in a covered bucket of moist sand in a cool room or basement where the temperature remains between 55 and 65 degrees. Hardy waterlilies can be left in the pond as long as the water doesn’t freeze. A good pump or water heater can help keep the pond and plants from freezing.