A paludarium, part aquarium and part terrarium, with water below and land and air above, is close to perfect moss country. The humid air over the waterline gives moss exactly the damp, sheltered conditions it craves, and the result can be a vertical green landscape running from the water up the back wall.
Where moss thrives in a paludarium
The sweet spot is the emersed zone: the banks, rocks, wood and background that sit just above the water in saturated air. There the moss stays constantly moist without being drowned, and grows lush. Moss fully underwater behaves as an aquatic plant, while moss high and dry near a vent will struggle, so the band around and above the waterline is where it does best. Many keepers run moss from a little below the surface up the hardscape, blending the aquatic and emersed forms.
Which mosses
The aquarium mosses double brilliantly here, since species like Java, Christmas and weeping moss grow happily both submerged and emersed, which suits a tank that straddles both. For the purely land portions, the resilient terrestrial cushion and carpet mosses used in vivariums also work in the high humidity. Java moss is the reliable workhorse to start with, spreading over wood and rock with little fuss.
Establishing and maintaining it
Attach moss thinly to the hardscape exactly as in an aquarium, tying or gluing a light layer over wood and rock, since a thick wad rots in the middle. Keep the emersed sections misted or within reach of the splash from a trickle or waterfall feature, which is why paludariums so often include moving water. Bright but indirect light and a humid, lidded environment do the rest. Trim to shape as it fills in, and the clippings will seed new growth wherever they land. For attaching technique and species detail see aquarium mosses.