A terrarium is a miniature ecosystem contained within an enclosed or semi-enclosed glass vessel, functioning much like a tiny, self-contained garden. It creates a relatively low-maintenance environment for specific plant types. Choosing the correct plants is paramount because the glass container imposes strict limits on the growing conditions, primarily concerning space, humidity, and light exposure.
Essential Plant Selection Criteria
The foundational rule for successful terrarium gardening is selecting plants that will remain small and slow-growing within the confined space. Fast-growing species require frequent, disruptive pruning and often lead to system failure. Plants should be miniature or dwarf varieties to ensure they do not press against the glass walls, which can promote disease development.
Plants must also tolerate the specific moisture conditions of the terrarium environment, and grouping plants with similar water needs is mandatory for a healthy habitat. Closed terrariums develop a high-humidity, perpetually moist atmosphere, while open terrariums require plants that can handle drier conditions and greater air circulation. Since most indoor terrariums receive only ambient light, all chosen species should thrive in medium to low indirect light, as direct sunlight can rapidly overheat the sealed container and cook the plants inside.
Plants Thriving in Closed, Humid Environments
Plants in closed terrariums benefit from the miniature water cycle that takes place inside the sealed container, where water transpired from the leaves condenses on the glass and returns to the soil. This self-watering system is perfect for species that require consistently moist soil and high atmospheric moisture.
Foliage Plants
Small-leafed foliage plants add color and texture to the mid-ground layer of the terrarium setup. The Nerve Plant (Fittonia spp.) is a popular choice due to its vibrant, patterned leaves and preference for consistently high humidity. Low-growing varieties of Peperomia, such as Peperomia orba ‘Pixie Lime’, are excellent candidates because they tolerate moist air despite their semi-succulent nature. Species from the Pilea genus, like the Artillery Plant (Pilea microphylla), are also frequently used for their fine, dense foliage and compact growth habit.
Ferns
Ferns are quintessential closed terrarium plants because they naturally inhabit the damp, shaded understories of forests. The delicate fronds of the Maidenhair Fern (Adiantum spp.) thrive in the near-constant moisture, provided the terrarium maintains extremely high humidity levels. Button Ferns (Pellaea rotundifolia) offer a slightly more robust texture with their small, round leaflets and are easier to manage in the enclosed space. Selecting miniature or non-spreading varieties of ferns prevents them from quickly dominating the small ecosystem.
Mosses and Ground Covers
Mosses serve as a lush, green carpet that helps regulate soil moisture. Sheet Moss and Mood Moss (Dicranum scoparium) are non-vascular plants that absorb water directly from the air and soil surface, flourishing in the high humidity. For a living ground cover that creeps along the substrate, Baby’s Tears (Soleirolia soleirolii) creates a dense, bright green mat of tiny leaves. These ground covers help reduce exposed soil, which can minimize the growth of undesirable molds and fungi.
Specialty Plants
For a more unique addition, certain specialty plants are perfectly suited for the stable, humid climate of a closed vessel. Miniature orchids, often called micro-orchids, thrive in these conditions, particularly Jewel Orchids (Ludisia discolor) which are prized more for their velvet, patterned foliage than their flowers. Carnivorous plants, such as certain tropical Drosera (Sundews) or Nepenthes (Pitcher Plants), can also be cultivated successfully in a closed terrarium due to their requirement for consistently moist, nutrient-poor, acidic soil and high humidity.
Options for Open, Dry Terrariums
An open terrarium, which lacks a lid or seal, is designed for plants that require excellent air circulation and low atmospheric moisture. The open container allows water to evaporate readily, preventing the saturated conditions that would cause rot in dry-loving species. This style of terrarium functions more like a decorative planter with high sides than a self-regulating ecosystem.
Plants suitable for this environment must be drought-tolerant and planted in a very well-draining substrate, typically a mix specifically formulated for succulents and cacti. The open top is essential for air exchange, which helps keep the foliage dry and prevents fungal issues common in humid, stagnant air.
Succulents and Cacti
Succulents are the most popular choice for open terrariums because their fleshy leaves and stems store water, allowing them to tolerate infrequent watering. Rosette-forming species like Echeveria and the translucent-leaved Haworthia are slow-growing and visually striking, fitting well into the confined space. Small, slow-growing cacti varieties, such as those from the Mammillaria genus, can be included, provided they are placed in a container with a very large opening to ensure maximum airflow and dry soil.
Air Plants
Air Plants (Tillandsia spp.) are an alternative option for open containers, as they do not require any soil and absorb moisture and nutrients through specialized scales on their leaves called trichomes. These plants are typically placed on decorative elements like rocks or driftwood, and they require high air movement to dry out quickly after their occasional misting or soaking. The open environment is mandatory for Tillandsia to prevent the base of the plant from rotting, which would happen quickly in a closed, humid setup.