Aquatic plants come in all shapes, sizes and functions to adorn both the outer edges of a water garden as well as within. While these water-loving plants may seem merely aesthetic, their value goes beyond beauty. Some plants oxygenate the water, some shade it from the sun and some convert waste into food. In other words, by adding plants to a water garden or pond, you not only enhance external beauty, but you also support a healthy ecosystem.
Water lettuce, water hyacinths, frog bits and fairy moss are just a few floating water varieties that shade the pond water from the algae-producing rays of the sun while free-floating around the pond. According to the University of Illinois Extension website, at least 50 percent of the water surface should be covered in floating plants to help regulate algae growth. But beware: Floating plants thrive in warm water, sending out shoots of baby plants. In some Southern states these plants can be invasive and illegal to grow.
Hardy Marginal Plants
Plants that tolerate water covering the containers they are planted in are called marginal plants. Marginal plants starve the growth of algae by using nitrates converted from fish waste and decaying debris as fertilizer. A "hardy" marginal has a zone corresponding to the zone of its environment. In order to regrow hardy marginals every season, overwinter them by cutting the foliage back to one to four inches and place them in a cool, damp and dark location that does not freeze. When the temperatures reach above freezing in the spring, move these plants back to the shelves of the pond or water garden.
Tropical Marginal Plants
Much like hardy marginal plants, tropical water plants line the outskirts of the pond on shelves and use nitrates as food. Unlike hardy marginals, though, tropical marginal plants thrive in warmer climates. A plant is considered tropical when its hardiness zone is greater than the environmental zone. Overwinter tropical marginals the same as hardy marginals except store them in an area that does not dip below 68 degrees Fahrenheit. As soon as the air temperature outside reaches a consistent 68 degrees, place these plants back on the pond shelves to regrow.
Water lilies, lotus and other lily-like aquatics are plants that shade the pond with foliage and keep down algal growth like floating plants; yet, like marginals, they use pond waste in the form of nitrates as plant food for the rhizome or tuber. These submergible water plants are also like marginal plants in that they come in both hardy and tropical varieties that are even overwintered in the same manner. However, to ensure healthy growth when reintroducing submergible plants, cover the rhizome in only six inches of water at a time until the leaves grow to the surface.
Oxygenating plants are healthy for fish as well as the overall maintenance of the pond because they transpire oxygen into the water through their leaves. Anacharis, cabomba, hornwort and parrot's feather are some common oxygenators that are completely submergible. And although fish thrive off the oxygen they emit, they also destroy the plants by foraging for food on the pond floor. Planting several bunches of oxygenators in a large container anchored in pea gravel may deter fish and keep plants in their place.