Willow Moss

True Willow Moss is a coldwater plant — which is unusual, because almost every moss sold for aquariums is tropical. Fontinalis antipyretica grows wild in cool, fast-flowing streams and lakes across Europe, North America, and northern Asia, anchored to rocks and submerged wood. Its dark olive-green shoots trail in the current, with small leaves set in three rows along the stem that give each shoot a keeled, three-dimensional shape rather than the flat sprays of Java moss.

Because it is a genuine coldwater species, it does best from 10 to 22 °C and slowly declines in a heated tropical tank, where it thins, browns, and eventually melts. It suits unheated rooms, coldwater setups, and native or temperate biotopes, and it is hardy enough to overwinter in an outdoor pond. Soft, slightly acidic to neutral water at pH 5 to 7.5 keeps it healthy.

Like other mosses it is attached rather than planted — tie or glue a thin layer to wood or stone and it grips the surface with rhizoids over a few weeks. Growth is slow to moderate, so it needs little trimming, and it copes with low to moderate light. CO₂ is not essential but firms up the growth. The two things that reliably harm it are warm water and very strong light.

The long, trailing shoots give good cover in shrimp and fry tanks and look natural draped over hardscape in a coldwater aquascape. Propagation is simply dividing a clump and reattaching the pieces. One caution when buying: several unrelated tropical mosses are sold loosely as 'willow' or 'weeping' moss, so confirm you are getting genuine Fontinalis if you specifically want a coldwater plant.