Salvinia molesta (Giant Salvinia) Care Guide
Salvinia molesta, giant salvinia, is a fast-growing floating fern (Salviniaceae) from Brazil; it is a major invasive species and is legally regulated in many regions.
Compiled by Aquairi from published sources · Published · Updated
Overview
Salvinia molesta, giant salvinia or kariba weed, is a free-floating aquatic fern of the family Salviniaceae. Its paired leaves bear distinctive hair-like strands that join at the tips to form eggbeater shapes, and a modified root-like frond hangs submerged below the surface.
Taxonomy
- Family: Salviniaceae
- Genus: Salvinia
- Scientific name: Salvinia molesta
- Common names: giant salvinia, kariba weed
Habitat
The species is native to south-eastern Brazil and thrives in slow-moving, nutrient-rich waters such as lakes, ponds, rivers and marshes. It cannot tolerate high salt concentrations. It has become established in tropical and subtropical regions worldwide, including several US states.
Tank requirements
- Temperature: 20-30 °C (68-86 °F)
- pH: 6.0-8.0
- GH: 3-16 °dGH
- Frond size: 0.5-4 cm
- Lighting: high
- CO2: not required
- Placement: floating
Growth and care
Growth is very fast: under optimal conditions the plant can double in dry weight every 2.2-2.5 days and form dense floating mats. As a vigorous nutrient sponge it helps absorb excess nutrients, but its mats can quickly shade other plants.
Propagation
Reproduction is exclusively asexual, through plant fragments and dormant buds (about five buds per node); the spores it produces are defective and do not form viable offspring.
Propagating Salvinia molesta (Giant Salvinia)
Overview
Salvinia molesta, also called giant salvinia or Kariba weed, is a free-floating aquatic fern. Its fronds are 0.5–4 cm long and carry a bristly, waterproof surface formed by hair-like strands that join at their tips into characteristic eggbeater shapes. Like all Salvinia, each node bears a trimerous whorl: two flat, green floating leaves plus one finely dissected, root-like leaf that hangs submerged in place of true roots.
Propagation Method
This fern does not propagate from seed: its spores are genetically defective and non-viable. Reproduction is entirely vegetative, by fragmentation and division. New plants grow from fragments that break off or from dormant buds that detach — and each node contains up to five buds, which is exactly why the plant spreads so fast.
Step-by-Step
- Confirm it is legal to keep giant salvinia where you live before propagating; if in doubt, do not.
- Choose a healthy mat with firm, upright green floating leaves and no rot.
- Gently pull or pinch the floating chain into segments, each keeping at least one node (a node carries the buds that will sprout).
- Float the segments on the surface of a separate, fully enclosed grow-out tank.
- Within days the dormant buds activate and form new daughter fronds, expanding the mat.
Conditions for Healthy Growth
- Temperature: 20–30 °C is optimal.
- pH: roughly 6–7.7.
- Light: high; bright light drives the fast surface growth.
- Water: nutrient-rich, slow-moving or still water; it is a powerful nutrient sponge.
- Cannot survive high salt concentrations.
Maintenance
Because the plant doubles in days, skim and thin the mat frequently to keep gas exchange and light reaching plants below. Bag all removed material and dispose of it sealed in household waste — never down a drain, into a pond, or onto compost.
Common Challenges
- Runaway growth: a thick mat shades and deoxygenates everything beneath it — thin aggressively.
- Uncontrolled spread: stray fragments cling to nets and hoses; rinse and inspect gear before reuse.
- Legal exposure: keeping or moving a regulated species can be illegal — verify local law first.