The ecological health of your pond is dependent on the kinds of aquatic plants you include in its landscape. A well-balanced pond has different types of plants, with each type providing a service. A properly landscaped pond is more likely to have clear waters, healthy fish and pond life, and less algae.
Plants growing beneath the surface of the pond oxygenate the water, and may be referred to as oxygenators. They thrive only in water, rooting in the pond's soil at the bottom or within a container placed in the pond. The majority of the plant, if not all of it, remains below the surface, though it may float its leaves at full growth. Oxygenators include parrot feather, water hawthorne, creeping jenny and water snowflake.
Floating plants, or floaters, move through the water, their long stems and root systems making them look untethered. The roots and plants both require a substantial amount of nitrates. This need aids in algae control, as the algae are less capable of flourishing without excess nitrates.
The floating plants, which include water lettuce, duckweed, pennywort and water poppy, also provide shade and hiding places for fish. Koi, and other species of fish, may nibble on these plants. Some floating plants, such as fairy moss, may be aggressive in growth and cover the pond's surface, effectively choking off any sunlight. Avoid this by anchoring your floaters in containers and moderating their growth.
Sometimes referred as edge plants or bog plants, marginal plants function like a retaining wall--providing anchors for the surrounding soil and reducing erosion. Marginal plants may be placed both outside the pond, along a boggy edge or just within the pond's perimeter.
Marginals include reedy grasses and cattails, canna, elephant ear, and umbrella palm. These plants tend to have dense growing habits and/or large leaves. The density of the marginal plantings helps protect the fish within your pond from predators such as herons or cats.
Like floaters, water lilies move across the pond's surface, providing shade and demanding nutrients. As with any plant, the water lily interacts with the immediate environment, providing oxygen, processing carbon dioxide, and exchanging nutrients.
Water lilies may be either tropical or hardy. Tropical water lilies have larger blooms, up to a foot across in size. The hardy water lily is smaller in size, and is a perennial, that is, it will go dormant in the fall and winter, and bloom again when the weather warms.