Frogbit Facts, Care, Planting, & Hardiness (Hydrocharis morsus-ranae)
European or common frog-bit, Hydrocharis morsus-ranae, is a floating perennial aquatic plant native to vast swaths of Eurasia, extending from Portugal to the Caucus Mountains and the British Isles and southern Sweden to northern Italy. The name frog-bit is nearly a direct translation of its Latin species name, morsus-ranae; the Latin word for “bite” is morsus and “frog” is rana. Some botanists believe that this is actually a misnomer, as the frogs seen supposedly feeding on the plant are actually catching caterpillars that the leaves host.
Often confused with water lilies in the Nymphaeaceae family, frog-bit grows rosettes of smaller heart-shaped leaves around 1 to 3 cm (0.4-1.2 in) in length and 1.2 to 6 cm in width (0.5-2.4 in) with a red or purple spongy underside. They produce miniscule (1.5 cm; 0.6 in) flowers with three white petals and a yellow center. Flowering occurs mid to late summer. Frog-bit usually grows at or just bellow the water’s surface, with very little vertical height. Instead, they use their hardy, fibrous root systems to anchor themselves to neighboring plants and rocks and grow outward.
European frog-bit plants are dieocious, meaning that each plant has either male or female reproductive structures and produce either pollen or seeds, respectively. Interestingly, one sex tends to dominate a growing area. Since a female plant cannot be pollinated without a male plant growing nearby, European frog-bit rarely reproduces in this manner. Instead, it sends out stolons or runners and grows outward from the central plant. Dormant buds may also detach from the central plant and be carried by the water downstream or sink to the bottom and regrow next spring.
Endangered in its natural habitat yet proliferating at a concerning rate as an invasive species, the benefits and risks of keeping frog-bit varies wildly depending on location.
Frog Bit Growth & Hardiness Considerations
European frog-bit grows is a particularly hardy and rapidly growing aquatic plant. In certain environments, European frog-bit has been found to spread 1.5 km (0.9 mi) over a single growing season. They do best in full sun and prefers soil that is mildly alkaline (7.6 to 7.8). European frog-bit requires tranquil water with a pH of 6.5 to 7.8 and have been found to do particularly well in water with high concentrations of organic compounds like those found in bogs as opposed to clay pits. Since part of their life cycle involves a winter dormancy, they can tolerate cold climates well and exist in areas with a minimum winter temperature of -28.8 °C (-20 °F).
How to Plant Common Frogbit:
Planting frog-bit is particularly easy. Separated stolons or a single rosette of leaves, can be added to a pond in late April. Since frog-bit is mostly free-floating, aquatic baskets or pots are not necessary. However, European frog-bit does best when there are areas of shallow water where it can attach itself to the pond perimeter. It is possible to grow a purely free-floating plant, but it will be less robust. If growing from seeds, sow them into very shallow water. The soil should be primarily composed of organic substrates, as European frog-pit does not do well in clay or aseptic tanks.
How to Care for Common Frogbit:
European frog-bit requires regular pruning to maintain the biodiversity of your garden. It can easily out-compete other aquatic plant species and dominate an entire pond in a short period of time. Trimming of the thick mats also minimizes the negative effect of fish mobility. Their roots can reach depths of 50 cm (19.6 in) so careful surveillance is necessary if kept with koi or goldfish.
Frog-bit naturally enter a dormant state at the end of fall. This involves a large portion of the plant, including all of the leaves, dying and the dormant buds—called turions, which originate from the stolons—falling to the bottom to wait out the winter. If you have pond fish, it is highly recommended that you remove the dead plant debris during late fall so it does not lower dissolved oxygen concentrations. If your pond is deep enough or you live in an area where it will not freeze through, no extra overwintering care is needed. Dormant buds can be brought inside in a container of mud and water if you live in an area where the entire pond will likely freeze solid.
Is Frogbit Toxic or Invasive?
European frog-bit is an invasive species in parts of Canada and the north west of the United States. It was first introduced to Ottawa, Canada in the early 1930s for arboretum cultivation, and had established itself in local waterways by the end of the decade. By the 1970s, European frog-bit had reached the United States. It is now considered established in Michigan, Wisconsin, New York and Vermont where its growth is likely facilitated by another invasive aquatic plant, the cattail (Typha spp.).
European frog-bit grows as dense mats that easily take over entire waterways and prohibit the movement of boats, swimmers, ducks, and large fish through the water. When frog-bit covers the surface of a pond, it blocks nutrient and sunlight absorption for the organisms living at greater depths. Frog-bit undergoes a natural die-off at the end of the season in which the plant dies and sinks to the bottom of the water. This is of particular concern because the dead matter lowers the dissolved oxygen concentration of the water, putting other organisms at risk of dying. The cultivation, possession, or transport of European frog-bit is prohibited in the states of California, Idaho, Illinois, Michigan, Minnesota, New Hampshire, New York, Vermont, Washington, and Wisconsin. Additionally, acquiring European frog-bit may be illegal in areas that tightly regulate non-native species importation, so always check your country or state legislation before purchasing the plant online.
Although nontoxic, dead or dying frog-bit should be cleared out of a pond to mitigate its potential negative effects on other vegetation and animals.
Will Pond Fish Eat Frogbit?
Gardeners and botanists have reported that European frog-bit is enjoyed by certain species of carp (Ctenopharyngodon idella Val.), beavers (Castor fiber), ducks, rodents, snails, and insects.