Salvinia natans aka Floating Fern

Salvinia natans is a small fern that floats on water. Its common names include salvinia and water fern. It belongs to the family Salviniaceae. Kew places its native range across temperate Eurasia into Indo-China and Java. Missouri Botanical Garden also lists northern Africa within its range. It is not native to Britain or Ireland. This aquatic fern is a perennial, though gardeners also grow it as an annual.

The plant has no true roots and forms spreading mats. Its simple stems have few branches or none at all. The leaves grow in whorls of three along each stem. Two leaves float, while the third stays below water. The floating leaves are pale green, oval, hairy, and unlobed. They reach about 0.06 feet [0.019 m] long. The submerged leaf is finely divided and serves as a root. The foliage mat rises about 0.08 feet [0.025 m] above water. The garden listing gives an overall height of 0.26 feet [0.08 m]. Listed spread reaches about 1 foot [0.3 m], though mats keep expanding.

This fern does not bloom, so flowers provide no display. Its leaf mats give it value in ponds and water gardens. Sporocarps sink to the bottom in autumn and spend winter there. They return to the surface once spring water warms. The plant loses its foliage seasonally. In suitable conditions, its spreading growth can cover more water than intended.

Grow it on still water in full sun or part shade. Put small groups on the surface after the last frost. Missouri Botanical Garden lists USDA hardiness zones 10–11. In colder gardens, keeping plants through winter calls for frost-free shelter. Lift some before the first autumn frost. An aquarium can provide a winter home. Another option is moist soil beneath about 0.17 feet [0.05 m] of water. Keep this container in a bright place without frost.

Growth is fast when conditions suit the plant. Use a net to remove surplus growth as needed. In frost-free climates, its spread can become aggressive. This makes control an important part of pond care. Missouri Botanical Garden reports no serious insect or disease problems. It also lists resistance to rabbits.