Place activated charcoal and pebbles in the bottom of the container for drainage and to keep the air clean.
Use peat moss potting soil because moss thrives on acidic soil. Make your own potting soil by mixing one part peat moss with one part garden soil. Add water to the mixture. Cover with aluminum foil and heat in an oven for 30 minutes at 200 degrees Fahrenheit. Allow the soil to cool.
Place the terrarium in an area that does not have direct sunlight. Too much sun will dry out the terrarium and kill the moss.
Keep the moss moist. Mist it with water in a spray bottle every two to four weeks.