In nature, mosses are often found in thin, sandy, rocky or infertile environments. This is because mosses obtain their nutrients from the air, rather than the surrounding soil, allowing them to grow on rocks, bricks, stones and other areas where conventional plants simply cannot grow. To create the poor-soil setting favored by mosses, combine equal measures of commercial potting soil, sand and clay. Scatter this blend across the bottom of the terrarium to create a layer of substrate at least 1 inch thick; moss has no roots, therefore, a deeper layer is unnecessary.
Gather mosses from rocks and trees, or simply purchase a block of sphagnum or peat moss from the local craft store. Crumble the moss and place the pieces into a blender. Combine ½ cup buttermilk and ½ cup water; add just enough dilute milk to cover the vegetation. Blend on low for one minute, spoon the moss mixture evenly over the terrarium soil, then cover the terrarium and set it in a warm place. The combination of heat, lactic acid and naturally occurring sugars will help rejuvenate the plant, encouraging the development of new spores.
Like all plants, mosses require a certain amount of light to flourish; however, they do not respond well to sunny conditions, primarily because direct sunlight tends to generate heat; mosses grow most actively in cool climates. To encourage moss growth, place the terrarium near a curtained window or several feet away from sun-drenched spaces. These dimly lit environments give healthy plants enough light to grow without causing the terrarium to overheat.
Mosses thrive in damp, moist climates. To ensure the terrarium has adequate humidity levels, spritz the moss three to four times a week with lukewarm water. Additionally, keep the lid on the terrarium as much as possible; this reduces air circulation, which slows the rate of evaporation and helps the terrarium retain moisture.