Freshwater pond habitats contain three general plant types: those that are floating, those that are rooted in deeper water and marginals or those that grow on the shallow shoreline. These plants improve water quality and provide cover and food for animal life. In the context of plants used in garden ponds, plants that are tropical in origin do not permanently grow in cold winter regions. Hardy aquatic plants are those that go fully dormant in winter and survive in cold, submerged water until spring.
Aquatic plants that float freely on the surface are called floating plants or sometimes oxygenators because they release oxygen from their leaves into the water. The floating plants serve multiple purposes. They shade the water from the sun, lower water temps that otherwise favor growth of undesirable algae. They absorb mineral salts from the water by the plant roots, helping purify the water and helping diminish algae blooms. Floating plants also provide a protective habitat and food for fish-egg hatchlings, called fry.
The muddy bottom of the pond is home to the roots and rhizomes of deep-water plants, although most of these plants typically grow in water from 2 to 5 feet in depth. These plants are fully submerged and have stems that are buoyant and hollow, allowing their foliage to float on the water's surface. Gorgon plant (Euryale), pond lily (Nuphar), waterlily (Nymphaea, Victoria) and lotus (Nelumbo) are examples. In aquatic plant nurseries and catalogs, waterlilies and lotuses are usually placed in a category unto themselves because their varieties are numerous.
Marginal plants are those that grow on the edges and ephemeral shorelines of the pond. Their roots may or may not be submerged in shallow water during the year. Cattails (Typha), flag (iris), papyrus (Cyperus), pickerel weed (Pontederia) and marsh marigold (Caltha) are examples.
Hardy Pond Plants
In the context of pond plants, those species tolerant and needing a cold, dormant period in winter are called hardy aquatic plants. As long as their roots and rhizomes remain underwater and do not freeze during the temperate climate's winter, they endure to sprout another spring once warmth returns.
Tropical Pond Plants
Aquatic plants that diminish or die in water temperatures that drop below 50 degrees Fahrenheit and will not tolerate any freezing temperatures are called tropical aquatics. Native to the year-round warm waters of tropical and subtropical regions, these plants are often temporarily placed in ponds over summer and removed in autumn in cold winter regions.