Under the water, on the water or by the side of the water, perennial plants bring a water garden to life for many years. The plants provide food and shade for water garden fish and help keep the water clean and free of harmful algae and bacteria. Water plants are more than a visual effect. They are an important part of the water garden ecosystem.
Pickerelweed (Pontederia cordata) is found growing in wetlands as far north as Minnesota and Nova Scotia and as far south as Argentina. The plant grows up to 3 feet tall with dark-green, arrowhead-shaped leaves. Violet-blue flowers 1 inch across bloom in late spring and summer in clusters. Plant pickerelweed around the edges of water gardens. The young leaves are edible and used in salads. Give the plant full or filtered sun and a a wet soil. Once established, it can take standing water up to 6 inches deep. The plant is hardy in U.S. Department of Agriculture climate zones 5 to 11.
Common hornwort (Ceratophyllum demersum) grows submerged in the water, providing food and shelter for the water garden fish. The plant produces stiff, bright-green leaves measuring up to 1-1/4 inches long and growing in clusters of 5 to 12 that look like a raccoon's tail. The stems grow suspended in the water or buried in the sediment on the bottom and reach from 8 to 12 inches tall. Tiny flowers grow under the water and are followed by dark, oval-shaped fruits. Common hornwort is hardy as far north as USDA zone 3 and as far south as South America.
Swamp mallow (Hibiscus moscheutos) is also known as swamp hibiscus and swamp rose mallow. The plant grows up to 7 feet tall, dying back in the winter and returning in the spring. The plant flowers with white or pink petals and crimson-red centers measure about 6 inches across. Plant swamp mallow in full sun and well-fertilized moist to wet soils by the side of the water garden.