Salvinia natans

Salvinia natans is a small, annual or short-lived perennial floating fern native to Europe and Asia, where it occurs in slow-moving rivers, ponds, lakes, and rice paddies across a wide temperate range. Each plant node bears two floating oval leaves and one finely dissected submerged leaf that functions as a root, absorbing nutrients from the water. The floating leaves are covered in water-repellent hairs, keeping the surface dry, and have a distinctive bright to medium green coloration. Salvinia natans is notable for its tolerance of cooler temperatures, remaining active at 15 °C — significantly cooler than most tropical floating plants — making it a rare option for cold-water and unheated aquariums. In autumn or when temperatures drop below about 10 °C, the plant produces spores and dies back, completing its lifecycle in temperate outdoor ponds before reappearing from spores the following spring. In consistently warm aquarium conditions it can persist as a perennial. Compared to Salvinia auriculata and the invasive S. molesta, S. natans is smaller, grows less aggressively, and is generally considered non-invasive outside its native range. It provides surface cover, shade, and nutrient uptake and creates a hiding place for surface-dwelling fish, fry, and shrimp. This species is an ideal choice for aquarists seeking a floating plant for temperate or subtropical setups, species tanks with cooler-water fish, or as a seasonal plant in outdoor ponds in temperate climates.

Water Parameters Salvinia natans tolerates a broad pH range of 6.0–8.0 and performs well in temperatures from 15–26 °C. It is one of the few floating plants suitable for unheated tanks in temperate rooms. Avoid sustained temperatures above 28 °C.

Lighting Moderate light of 40–100 µmol is sufficient. Outdoors in natural sunlight, growth is most robust. Indoors, a quality full-spectrum LED sustains healthy growth.

Seasonal Behavior In outdoor ponds in temperate climates, this plant behaves as an annual — it produces spores as temperatures drop in autumn and recolonizes from spores in spring. In indoor aquariums at stable temperatures above 15 °C, it persists year-round.

Surface Flow Prefers still or very gently moving water. Surface agitation damages the delicate floating leaves and disrupts the water-repellent air layer on the leaf surface.

Nutrition The submerged root-leaves absorb nutrients directly from the water. In nutrient-poor systems, supplement with a diluted all-in-one liquid fertilizer for floating plants.

Maintenance Thin regularly when growth is vigorous during warm months. Remove yellowed or damaged fronds. In outdoor ponds, collect and remove the bulk of the plant before the first frost to harvest spores; alternatively, allow natural die-back and recolonization.

Common Problems Sudden yellowing usually indicates a nitrogen deficiency or water temperatures outside the preferred range. Browning fronds are often caused by excessive surface agitation or mechanical damage.