Select a container, such as an aquarium, for your terrarium. Containers can be made from anything you choose, but an aquarium provides an enclosed humid environment, which is perfect for ferns.
Pour a layer of sand or pebbles, approximately 1 inch deep, on the bottom of your terrarium. This layer provides drainage for your terrarium.
Pour a layer of activated charcoal over the layer of sand. The activated charcoal acts as an air filter in an enclosed environment.
Place a layer of sphagnum moss over the charcoal. The moss acts as a barrier to prevent the soil from settling down into the lower layers.
Add a layer of soil over the moss. Make the soil deep enough to accommodate the roots of your plants.
Plant your ferns and other plants as desired. Take care to arrange them, so they are not touching the side of the terrarium and have enough room between them. f you choose, you can also add ornaments to your terrarium.