Terrarium

A terrarium is a glass container designed to house soil and plants in an environment differing from the surrounding atmosphere. Though commonly sealable, terraria may be fully closed or left open, depending on the species cultivated. They are widely used as decorative objects and also serve educational and horticultural purposes. Closed terraria create self-sustaining microenvironments, while open designs support plants adapted to drier conditions.
Closed terraria function through a miniature water cycle. Light enters through transparent walls, enabling photosynthesis and warming the interior. Moisture evaporates from soil and foliage, condenses on the glass, and returns to the substrate, creating a balanced hydrological loop. Open terraria, by contrast, lack this sealed cycle and provide greater ventilation, making them suitable for species that require lower humidity.

History

The terrarium originated in 1842 when botanist Nathaniel Bagshaw Ward unintentionally created the first example after observing a fern spore germinate inside a sealed jar that he had neglected. This discovery led to the development of the Wardian case, which gained popularity in Victorian England as both a scientific tool and fashionable household ornament.
Ward’s cases proved invaluable for transporting live plants over long distances. British species shipped to Australia survived months of sea travel, as did Australian species sent to London. These trials demonstrated that sealed environments could sustain plant life without external ventilation. Wardian cases soon became instrumental to Kew Gardens and to botanical exchange across the British Empire, including the movement of African agricultural products such as spices and coffee to Europe.

Types

Terraria fall broadly into two categories: closed and open.

Closed terrarium

Closed terraria replicate the humid, sheltered conditions of tropical ecosystems and are ideal for moisture-loving plants such as ferns, mosses, orchids and air plants. Their sealed structure allows continuous water circulation, creating a self-sustaining microclimate. To prevent fungal or algal proliferation, the container is typically opened once a week for ventilation.
Indicators of imbalance include wilting plants or a lack of condensation, both of which suggest insufficient moisture. Watering is usually done with a fine spray. Closed systems benefit from specialised soil media; a common choice is peatlite, a sterilised mixture of peat moss, vermiculite and perlite, designed to optimise drainage and minimise microbial risks. Some keepers introduce springtails, small arthropods that consume mould and help maintain a healthy substrate.

Open terrarium

Open terraria lack a sealed lid and are designed for species requiring lower humidity and better airflow. These include temperate plants and those native to arid habitats. Because heat can accumulate rapidly in a closed system, open terraria provide safer conditions for plants sensitive to high temperatures. They require more frequent watering but carry lower risks of microbial disease due to reduced moisture levels.

Difference from a Dish Garden

Although similar in appearance, an open terrarium differs from a dish garden in its ability to retain humidity. Transparent terrarium walls trap moisture, enabling a humid environment even when open, whereas dish gardens do not create additional humidity. Terraria must not be placed in direct sunlight because the glass walls amplify solar radiation, risking foliage burn. Dish gardens, especially those containing sun-tolerant species, can withstand direct light.
Succulents and cacti generally fare better in dish gardens than in terraria, as they require full sunlight and low humidity—conditions more difficult to maintain in glass enclosures.