A terrarium is usually a sealable glass container containing soil and plants and can be opened for maintenance to access the plants inside. However, terraria can also be open to the atmosphere rather than being sealed. Terraria are often kept as decorative or ornamental items. Closed terraria create a unique environment for plant growth, as the transparent walls allow for both heat and light to enter the terrarium.
The sealed container combined with the heat entering the terrarium allows for the creation of a small-scale water cycle. This happens because the moisture from both the soil and plants evaporates in the elevated temperatures inside the terrarium. This water vapour then condenses on the walls of the container and eventually falls back to the plants and soil below.