Christmas Moss

Scientific name: Vesicularia montagnei

Origin: Brazil

Growth: medium to slow, 3–5 cm

Light and CO2: medium light; CO2 optional

Placement: attach to wood or stone

Propagation: divide and re-tie

Christmas Moss (Vesicularia montagnei) grows in flat, branching fronds arranged a little like the side branches of a fir tree, which is where the name comes from. It is a South American moss and grows more slowly than Java Moss, and it is a touch more demanding: it looks its best under medium light with a little water movement, and it stays neater and denser. Because the fronds pack tightly it makes better cover for baby shrimp than a loose moss, and the dense mat holds more biofilm, the film of microbes that shrimp graze. Like all mosses it has no roots. Attach it to hardscape rather than pushing it into gravel; it takes everything it needs from the water. Starting height is 1–3 cm and an established mat sits around 3–5 cm. Once it has settled it spreads outward across the surface it is tied to, and an occasional trim with scissors keeps the fir-branch shape instead of a shapeless clump.

Water: adaptable; kept in the same range as most tropical tanks. Gentle flow helps keep debris off the fronds, which otherwise trap mulm and brown off.

Planting: tie a thin layer to wood or stone with cotton thread, or use a dab of aquarium-safe cyanoacrylate gel glue. Spread it thinly; a thick pad shades its own base.

Light and feeding: medium light (Tropica lists about 0.5 W per litre) gives the tightest growth, though it survives lower. CO2 injection (carbon dioxide gas added to speed plant growth) is optional and not needed. A weak liquid fertiliser dose is enough. Trim as it thickens so the inside stays green.