Propagating Salvinia molesta (Giant Salvinia)

How to multiply giant salvinia by fragmentation in a closed tank, with strict warnings about its status as one of the world's worst invasive aquatic weeds.

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.