Layers on layers, yo.
Glass terrariums are hit or miss for me. On one hand, watching my plants grow from root to leaf is an incredible experience for any plant lover.
On the other…Glass containers will kill your plants if you do not know what you are doing.
The key to keeping a healthy terrarium thriving lies in the layers – specifically, the layers of soil, rock, activated charcoal, and moss at the bottom of your container.
Layers of these materials keep roots from rotting, as glass containers have no built in drainage. You have to create a drainage system yourself, starting with rocks at the bottom.
After you place the rocks at the bottom, add a layer of activated charcoal to purify any water that seeps through. This will keep your terrarium from forming a layer of pond scum at the bottom.
Then, add your soil. I use regular potting soil because the only plants you should be placing in a terrarium should be moisture tolerant. Succulents, cacti, and air plants should never go in a terrarium, as they will quickly rot from the lack of drainage.
Water your terrariums less than traditional pots, especially if the container has a lid. The lid will keep additional moisture in the terrarium. I water my small terrarium seen above on a monthly basis.