12 Best Pond Plants That Clean & Filter Pond Water 2022 [Updated]
Submerged, floating, and emergent plants bring so many benefits that surpass their mere ornamental functions. Apart from naturalizing outdoor ponds and enhancing their overall appearance, their physical features provide shade and complex structure. They meet the sustenance and habitat requirements of a wide range of animals, but it’s their functional attributes that may truly make them worth cultivating in ponds.
Semi-aquatic and aquatic pond plants have highly-adapted vegetative features allowing them to obtain most of their needs in water. Just as the roots of terrestrial plants take up nutrients, heavy metals, and pollutants from the soil, those of aquatic plants can directly obtain them from the water column or from waterlogged substrates. This ability to take up free-flowing compounds (specifically ammonia and nitrates) is central to their role as living filters in a pond.
In any type of enclosed aquatic system, the removal of nutrients is vital as their accumulation can result in toxic conditions. Plants with a high metabolic rate can significantly reduce pressures on both artificial and bio-filters as they are simply hungry for nutrients. These plants also compete with algae, keeping their growth to a minimum and thereby preventing algal blooms. They can be placed in strategic areas where both their physical and functional attributes are maximized.
1) Hornwort (Ceratophyllum demersum)
An aquarium and pond favorite due to its appealing structure and ease of care, the humble hornwort is a fantastic oxygenating plant. Maintaining a fully submerged habit, its stems can grow up to 3 meters (10 feet) tall. These can quickly accumulate to form a dense, underwater bush in ponds with high nutrient outputs. The whorled leaves, which are quite stiff, provide surfaces that benefit healthy microbial communities and protect newly-hatched fish.
Due to its rapid growth rate, hornwort takes up considerable nutrients from the water column and substrate. Its fragments are able to persist even as they are removed from the main plant and become free-floating. Cuttings are thus frequently used for propagation. This highly resilient species also produces biochemicals that inhibit phytoplankton and algal growth.
Note that mature hornworts may need to be trimmed or restricted to pots as they may exhibit weed-like growth. They are most likely to compete with other submerged plants in still or slow waters, especially when they are cultivated in warm temperatures.
2) Water iris (Iris laevigata)
Ideal for growth along the shallow margins of a pond, the water iris is a stunning ornamental plant with favorable functional qualities. Its root system can aid in preventing shore erosion while taking up excess nutrients that have seeped into the substrate. Its emergent stems afford newly-hatched fry and pond visitors protection as they enter and exit the system.
High-nutrient concentrations are beneficial to the growth and survival of I. laevigata seedlings and mature plants. Even the width of the leaves is affected by the availability of nutrients in the soil. Fish ponds, which produce significant amounts of waste, are thus ideal for water iris cultivation. This species favors slightly acidic substrates and must be exposed to ample sunlight for maximum bloom production.
While aiding in water filtration, irises will surely bring desirable color and attract many pollinators to your pond’s margins. The decorative effect of their shoots is most spectacular when they are arranged in dense clumps. A generously planted water iris stand would also be best for rapid nutrient removal.
3) Water hyacinth (Eichhornia crassipes)
Known for its exceedingly rapid growth rate and tendency to spread, the water hyacinth is remarkably efficient at nutrient removal. It has even shown potential for use as a biological treatment for highly-contaminated wastewater. Its vegetative organs are able to bioaccumulate a wide range of chemical compounds, including dyes, heavy metals, and inorganic contaminants, apart from nitrates and ammonia.
Though it is quite an attractive plant and is undoubtedly one of the best species for water filtration, its rate of spread may dismay many pond owners. In the absence of competitors, water hyacinth may spread quickly enough to cover the entire pond’s surface in just a few weeks. It has thus been labeled an aggressive weed or invasive plant in many areas.
To limit its spread in an ornamental pond, water hyacinth may need to be physically eradicated from the water’s surface. Fully-grown plants can be removed by hand in small quantities. They can also be removed in large quantities with a rake or seine. All plant parts should be disposed of properly to prevent them from entering public waterways.
4) Soft rush (Juncus effusus)
The soft rush is a highly textural plant that can thrive along the margins or edges of a pond. It can tolerate minimal flooding and prolonged exposure to a few inches of standing water. Clumps tend to spread outward from the pond’s edge if the surrounding substrate is kept moist. To keep the roots secure, it is advisable to place rocks around the crown of the plant.
Juncus effusus has been shown to aid in the removal of nutrients from sewage water and agricultural runoff. The roots, along with the biofilm that accumulates on their surfaces, are able to efficiently take up nitrogen and phosphorus compounds. This highlights the plant’s potential not only as a living filter along a pond’s margins but also as a sieve through which runoff may be stripped of nutrients before entering the pond.
Though soft rush is frequently used for landscaping and pond design, it does have the tendency to become invasive. Its rapid metabolic rate and capacity to self-seed allow it to spread quickly. Mature plants may need to be plowed or topped regularly to minimize spread.
5) Water mint (Mentha aquatica)
Another low-maintenance plant favoring shallow, marginal conditions in ponds, M. aquatica is a flowering perennial with multiple uses. It can be cultivated as an emergent wildflower to attract pollinators, harvested to make herbal infusions, or planted in large densities to treat wastewater.
In constructed wetlands containing large stands of this species, significant reductions of coliform bacteria, organic nutrients, and heavy metals have been shown. It is evident that water mint has a high phytoremediative potential.
Water mint is characterized by its 4-sided shoots, which can grow up to 35 inches (90 cm) long. Its serrated, bright green to purple leaves are ovate and variably hairy. In summer, dense inflorescences arise on the tips of the stems. The root system, which is largely fibrous, expands via rhizomatous growth.
6) Fanwort (Cabomba aquatica)
A fully submerged perennial, fanwort has been popularized by the aquarium industry due to its appealing features and ecological benefits. It is known for being an oxygenator and for aiding in the removal of carbon dioxide from the water column. Apart from taking up nutrients to meet its metabolic demands for rapid growth, this species is able to bioaccumulate heavy metals.
The beautiful shoots of C. aquatica can turn any underwater landscape into a highly structural ecosystem where many types of small animals can thrive. Its floating leaves allow the shoots to remain upright, maintaining a graceful appearance that seems to defy gravity.
Propagation of this species is incredibly easy and straightforward as new plants can arise from detached stems. The nodes may readily produce adventitious roots. These can quickly become established once they come into contact with bottom substrates.
7) Water lilies (Nymphaea spp.)
Oftentimes, water lilies are the first to come to mind at the thought of plants for ornamental ponds. This highly popular group of floating aquatic perennials consists of a few dozen tender species. Some of the most commonly grown cultivars are those of N. odorata, N. capensis, N. elegans, and N. alba. The decorative features of some stunning hybrids have earned them the RHS Award of Garden Merit.
Water lilies aid in keeping the water column clear in two principal ways. First, their large lily pads provide shade, which is vital for the prevention of algal blooms. Second, their vegetative parts are able to accumulate considerable amounts of nitrogen and phosphorus-rich compounds. Removal efficiency may be associated with seasonal conditions as these affect the rate of plant growth. Some species have also been shown to adsorb toxic elements from effluents.
To be effective at nutrient removal, Nymphaea leaves should be in good condition and should not, themselves, be rotting on the pond’s surface. Decomposing leaf material releases nutrients into the water, so these should be removed as soon as they are spotted.
8) Cattails (Typha spp.)
Present along the edges of virtually all large freshwater waterbodies in the Northern Hemisphere, cattails number around 30 species. Their predominant and distinctly unifying feature comes in the form of a sausage-shaped inflorescence which opens up to reveal thousands of cottony seeds.
With stems that are fully aquatic to semi-aquatic, cattails are tolerant of partial submersion as their spongy stems are capable of transmitting necessary oxygen to their root systems. They spread via rhizomatous growth or via their seeds, which are capable of germinating in muddy substrates.
Typha species are generally efficient at nutrient removal due to their rapid rate of growth. T. latifolia, a common cattail that is often referred to as a bulrush, has shown potential for nitrogen and phosphorus removal in wastewater. Its cultivation has thus been proposed as an eco-friendly means of wastewater remediation. Simply planting a small colony along the margins of a pond should provide supplementary filtration.
9) Watercress (Nasturtium officinale)
With its rich history of cultivation, watercress is one of the earliest semi-aquatic plants to be grown as a vegetable. This nutritionally-rich crop is now frequently grown in hydroponic systems, though the water must be supplemented with nutrients to obtain favorable yields.
A pond or aquaponic system with its own community of waste-producing fish would be perfect for watercress growth. The presence of pollutants or heavy metals in the water, however, may affect how safe the vegetables are for human consumption.
Both nitrogen and phosphorus are readily taken up by the roots of N. officinale and are most efficiently removed during periods of maximum plant growth. The removal of nitrogen-based compounds is also influenced by fluctuating oxygen concentrations in the water column. A high concentration of nutrients has been linked to the rapid increase in biomass of this species, hinting at how potentially invasive species may rapidly spread in nutrient-rich systems.
10) Water lettuce (Pistia stratiotes)
Known for its remarkable capacity to spread quickly, water lettuce is an extremely productive aquatic plant. It favors relatively still or slow-moving waters in subtropical to tropical regions. The highest growth rates occur at a temperature range of 22 – 30˚C (72 – 86˚F) and at slightly acidic pH levels. A high nutrient load should result in boosted growth as this species can quickly assimilate nitrates and phosphates.
This floating plant has shown potential as a natural bioremediator in eutrophic stormwaters. Its rate of nutrient removal is markedly superior to that of many other aquatic species, though this is invariably affected by ambient conditions.
The main problem with using water lettuce as a natural filter is the difficulty in controlling or reducing its spread. It is unfortunately listed as an invasive species in countries where its wild colonies have damaged many natural freshwater systems. Mature plants reproduce by sending out offshoots. These may eventually separate from the mother plant and form their own clonal colonies elsewhere.
11) Variegated water celery (Oenanthe javanica)
A highly edible herb, O. javanica is an aquatic plant with both ornamental and medicinal uses. It forms large clumps along the shallow margins of swamps, streams, marshes, and lakes. Though it thrives best in tropical climates, it is able to tolerate a wide range of ambient temperatures. Some cultivars may even persist in frosty conditions.
Fertile soil or water is most likely to produce the highest yields of variegated water celery. In areas where it naturally grows as a marginal plant, it aids in filtering out excess nutrients from the shoreline. A high intake of nitrogen and phosphorus tends to significantly increase the biomass of its roots and shoot, producing more edible material for wild grazers or for use as a culinary vegetable.
The downside to growing this natural filter outside of its native range is its rapid spread. If its growth can be controlled, it would be a desirable ground cover plant for diversifying texture, adding color, and hiding liner in garden ponds.
12) Taro (Colocasia esculenta)
C. esculenta is an economically important species. It is frequently cultivated as an ornamental pond plant due to its magnificently large leaves and as a crop vegetable due to its tasty corms. Taro is so entrenched in the history of many tropical countries that dozens of cuisines have a use for its flavor and texture. Both the large corms and leaves are a testament to its productivity.
Of course, this plant needs to have access to nutrient-rich substrates to produce its most important features. It favors fertile soils in consistently moist or wet areas, such as the margins and edges of slow-moving water features.
As its vegetative parts grow, taro actively removes organic matter, nutrients, and toxic pollutants from the soil and water surrounding its root systems. It has been proven to reduce nitrate and phosphate concentrations in raceways that received wastewater. It is also capable of bioaccumulating heavy metals, such as lead and cadmium. If your pond’s water quality is often poor despite a functional filter, try introducing taro to its margins.