Tropical water lilies (Nymphaea spp.) are flowering pond plants that provide needed shade to the pond in addition to hiding and egg-laying places for pond fish. Tropical water lilies also absorb certain nutrients in pond water that otherwise would feed harmful algae. Tropical water lilies are perennials, but they're hardy only in USDA zones 9 and 10, where winter temperatures stay above 30 degrees F. In colder climates, tropical water lilies are planted as annuals in ponds or over-wintered indoors.
Plant tropical water lilies in 10- to 14-inch-diameter fabric pots. Fill them with loamy garden soil about 2 inches from the top, placing two to four fertilizer tablets in the middle of each. Top off the soil with 1 to 2 inches of pea gravel.
Place the tropical water lily in the pond, setting the plant so that the water surface is about 6 inches above the water lily's crown. Gradually lower the tropical water lily to a depth of about 12 inches as it grows, ensuring that the leaves stay floating on the water surface.
Feed tropical water lilies once every month throughout the spring, summer and early autumn with fertilizer tablets made for aquatic plants. Follow the dosage instructions on the label.
Over-winter tropical water lilies by removing them from the pond and placing them in an aquarium indoors, if you live in a cold-winter climate. Remove the plant and keep it indoors in water that's 70 to 75 degrees F when the pond water temperatures drop below 70 degrees.