Limnobium laevigatum is a wonderful aquatic plant for adding color and complexity to both indoor and outdoor water features. Commonly called smooth frogbit, South American spongeplant, or Amazon frogbit, its colonies are known for their quick capacity to proliferate. Along with other frogbits, tape grasses, and waterweeds, it is a member of the Hydrocharitaceae family of aquatic flowering plants. The best places to search for its natural stands are the freshwater systems of tropical to subtropical Central and South America.
Smooth frogbit naturally occurs as a floating species, with smooth, glossy, and bright green leaves that lie prostrate on the water’s surface. Mature leaves, which may arise on slightly lengthier petioles, may maintain an emergent habit. Juvenile leaves are distinguished by their spongy undersides. Their sponginess is reduced as the leaves mature and grow to a maximum diameter of about 1.6 inches (4 cm). The flowers of this species are generally solitary, small, and white. They develop into berry-like capsules containing hairy seeds.
In terms of appearance, the mature foliage of smooth frogbit can easily be mistaken for those of water hyacinth (Eichhornia crassipes). Unlike the latter, the petioles of L. laevigatum do not maintain an inflated appearance. The small, floating seeds of this species look similar to those of duckweed (Lemna spp.).
Facts, Benefits & Uses of Smooth Frogbit
In outdoor ponds, the presence of controlled populations of smooth frogbit can help prevent algal blooms. The rosettes of floating leaves, which may eventually form expansive mats, can serve as a vital habitat for many small amphibians and juvenile fish. As the glossy leaves can block sunlight, they aid in maintaining water temperature. Despite these many benefits, however, this species should be cultivated with caution.
Smooth frogbit can spread in an aggressive manner, especially in relatively still waters with rich concentrations of nutrients. If the leaves are dense enough to block out copious amounts of light, they can deprive the water column of oxygen and stifle the growth of other freshwater plants and microbes. Escaped populations may need to be controlled by mechanical or chemical means.
In fully enclosed ponds and aquariums, a well-maintained colony of smooth frogbit can serve as a vital food source for herbivorous fish and snails. Nonetheless, keep in mind that the seeds or fragments of this species are easily dispersed by visiting wildlife or via overflowing pondwaters entering public water systems.
Smooth Frogbit Growth, Hardiness & Climate
Smooth frogbit grows best in calm, slow-moving bodies of freshwater. Moderately warm conditions bring out the best features of its glossy leaves, whereas cool waters tend to slow its growth and spread rates. Though it is known for being highly adaptable to a wide range of ambient conditions, it prefers to be situated in tanks or ponds with a water hardness that is maintained at 0 – 12 GH. Full sun exposure or high illumination (at least 10 – 12 hours per day), should help prevent the occurrence of diseases.
Hardy to USDA zones 4 – 10, smooth frogbit can quickly form dense mats. In the absence of natural predators or competing plants, it may block entire waterways and impede recreational activities. Make sure to keep this in mind if you intend to purchase this plant for aquascaping purposes. While it can definitely give your water feature a lush appearance in no time, its population may need to be contained.
The availability of nutrients is definitely a major limiting factor to the spread of frogbit. Floating debris, and oxygen-poor, fully stagnant water (which ironically is a potential effect of its aggressive spread), may also compromise the quality of its leaves and roots.
How to Plant Smooth Frogbit
Smooth frogbit is remarkably easy to propagate. Able to spread via vegetative or sexual means, its colonies can expand via the dispersal of fragments or seeds. This species isn’t exactly “planted” in the typical sense, as its seeds or fragments need not be buried in soil to germinate or grow. Instead, they can be left to float on the surface of a pond or tank. When provided with optimal lighting and nutrient conditions, they should begin to produce new tissues in no time.
In aquariums, smooth frogbit tends to spread via runners that produce new plantlets. These can be pinched off from the mother plant and placed into another aquarium or section of the pond. Prepare the water’s surface by removing debris. Gently lower the plantlets onto the water’s surface. Minimal water movement is key to encouraging new growth.
Plantlets can also be left on their original runners. As these mature, they tend to separate from the mother plant on their own. Their leaves should grow faster and reach larger sizes if they are attached to runners, from which they can obtain additional nutrients, for as long as possible.
How to Care for Smooth Frogbit
Proper care and maintenance would definitely improve this plant’s longevity. Healthy smooth frogbit colonies should brighten up water features without attracting pests and pathogens. To maintain the appearance of smooth frogbit leaves, avoid getting water on their upper surfaces. Dirty droplets from an aquarium cover, for example, can pool on the surfaces of the leaves and eventually trigger the onset of leaf rot.
Well-maintained water quality is critical for this species’ health. Though it naturally aids in removing excess nutrients from freshwater systems, toxic concentrations can damage the roots and encourage the growth of harmful pathogens. Regular water changes, coupled with monitoring techniques for ensuring maintained temperature and pH levels, should benefit the leaves. In ornamental ponds, the nutrients from fish waste should boost the growth of new leaves. If you notice that the runners have yet to produce new plantlets, especially in aquariums, you may need to fertilize the water.
How to Winter Smooth Frogbit
As smooth frogbit is native to regions that rarely experience harsh winter conditions, it is unlikely to persist as a perennial in northern temperate zones. A sudden drop in water temperature can stress the tissues of this plant and cause its suspended roots to die back. In cool climates, it would be necessary to provide additional heating during winter months. This should help stabilize water conditions and encourage continuous plant growth.
If your pond is situated in a temperate zone, you can overwinter your delicate smooth frogbit colony by moving it to a warmer location. Gently fish out the floating foliage and place them in a temperature-regulated indoor aquarium or drum of pond water. To encourage this plant to conserve its energy through winter, it is advisable to minimize lighting and withhold the provision of supplementary nutrients.
Is Smooth Frogbit Invasive or Toxic?
L. laevigatum is not a toxic plant and is generally safe to grow around fish and other domesticated pets. Nonetheless, it would be prudent to grow it with caution as it has the tendency to become an invasive plant. Introduced into continents outside of its native range as a low-maintenance aquascaping plant, its escaped populations have caused significant damage to many natural waterways. In California, for example, its colonies have threatened the ecology of several important wetland systems.
Smooth frogbit fragments and seeds are dispersed by boating activities, waterfowl, tidal action, wind, and currents. When these are transported into slow-moving waters, they can quickly self-propagate to create new colonies. Chemical growth regulators may occasionally be necessary to prevent weed-like growth or treat severe infestations.
Is Smooth Frogbit Edible? Do Animals Eat It?
Though smooth frogbit is non-toxic, it is not generally consumed by humans as food. Many aquatic animals can benefit from the nutrients in their floating foliage. Herbivorous fish, turtles, and some invertebrates will readily feed on this plant. Some species of freshwater fish, particularly those in the Amazon River, may rely on several frogbit species as a major part of their diet.
Where to Buy Smooth Frogbit & Seeds? (UK & US)
Limnobium laevigatum is frequently sold in aquascaping stores throughout its native range. Fish shops, particularly those that sell aquarium gear and aquatic plants, tend to carry this easy-to-grow species. If you’re located in the US or Europe, make sure to double-check your locality’s list of prohibited plants before placing an online order for this species.
