The first layer in your terrarium should be pebbles. This will ensure proper circulation of water throughout the system. I like to add some glass as well. I normally try to add about 1 inch of drainage material to a terrarium. Use a bamboo skewer to level the pebbles in the container.
Add your activated charcoal next. If the opening to your terrarium container is narrow try rolling a piece of paper into a cone and pouring the charcoal in through the cone. You only need enough charcoal to lightly cover the pebble layer.
Now it is time to layer your small bits of soaked and dried sphagnum moss to the terrarium. The bits of moss should be no larger than the opening of your terrarium container. Try to completely cover the pebbles and charcoal as the moss will act as a filter and keep soil from drifting into your bottom layers. This layer is optional- if you prefer to have your charcoal and pebbles mix up in your soil you can leave this step out. Use a bamboo skewer to tamp the moss down.
Mix two parts potting mix with one part sand to ensure proper drainage. If your terrarium is on the small side (decorative bottle rather than aquarium), you may want to increase the amount of sand and decrease the amount of soil. Add distilled water to make damp but it is easier to transfer to terrarium when it is dry. Remember - you can always add more water to your final terrarium but it is difficult to remove!
You are now ready to add your soil. You should have enough soil to fill about 1/4 to 1/3 of your terrarium container. I would recommend using about 1/2 of the portion you have set aside for your terrarium and then adding the rest after you have planted your largest terrarium plants. Add the soil by scooping spoonfuls into your paper cone and tamping down with a skewer.
Once you have layered your dirt into the terrarium you'll want to mist down the soil. Soil will need to remain damp throughout the life of your terrarium to support your plant growth.
This is the second post in my series "How to Make a Terrarium"
Previous Post: Materials and Tools