Will Chlorine Kill Water Lilies?

Some Like It Cold

• Hardy and tropical water lilies are often divided according to their preferred water temperatures, as opposed to U.S. Department of Agriculture plant hardiness zones, which are more suited to plants growing on land. Hardy water lily species go dormant in the winter and can survive ice on top of the water as long as their rhizomes do not freeze. Some hardy species will grow in USDA zones 3 and 4. Tropical water lilies will grow in outdoor ponds as long as the water temperature does not drop below 60 degrees Fahrenheit. Most tropical species will grow in USDA zones 8 through 11.

Helping Kill Algae

• Chlorine evaporates from water within hours, and adding chlorinated water to a pond of fresh water should not affect aquatic plants or fish. Interestingly, chlorine plays a useful function helping manage algae in water gardens until aquatic plants and fish can do the job. If you grow water lilies in containers, let the water sit for one or two days to get rid of the chlorine before you plant them. After that, replace evaporated water with chlorinated tap water until the water is balanced, meaning that the plants and fish can hold off the algae. This will typically take about 60 days.

The Stubborn Chloramine

• Some municipal water systems treat water with chloramines, made by mixing chlorine with ammonia, to protect it from toxic organisms as it moves through water systems. Chloramine is more stable than chlorine and doesn't evaporate as quickly. Two types are used for drinking water and a third for swimming pools. The effect of chloramines on water lilies and other aquatic plants is unclear, but if your water supply contains chloramines, most garden supply centers sell activated charcoal or other products that will remove it.

Yellow Pond Lily to the Rescue

• The fragrant water lily (Nymphaea odorata) and other aquatic pond lily species are easy to grow and are widely grown in ornamental ponds. If your pond is connected to other ponds or slow-moving streams, water lilies can spread invasively, forming floating, dense mats wherever they go. Mats of water lilies over areas of open water provide excellent habitats for fish. If they are not managed, however, they can cover the water, depriving it of oxygen. University of California horticulturalists recommend the yellow pond lily (Nuphar polysepalum) a non-invasive, native pond lily that is found naturally from Alaska to California.