Succulents are drought-adapted plants that store water in their fleshy leaves, stems, or roots, making them perfectly suited for arid conditions. A traditional terrarium is an enclosed container that operates as a self-contained, high-humidity micro-ecosystem. The answer to whether these two environments are compatible is generally no; a succulent will not survive long in a standard, closed terrarium. However, it is possible to create a highly modified, open container display that mimics the aesthetic of a terrarium while meeting the specific needs of these desert-adapted plants.
The Fundamental Conflict: Humidity and Drainage
Succulents thrive in environments characterized by bright light, high airflow, and soil that dries out quickly after watering. Their native arid habitats led them to evolve mechanisms to endure long periods of drought, preferring low humidity (often 10 to 30 percent). A closed terrarium creates the opposite microclimate, trapping moisture and generating an environment with near-constant high humidity and stagnant air.
This environmental mismatch leads to two primary problems. First, the lack of air circulation and high moisture content around the plant’s roots encourages fungal diseases, such as powdery mildew, and bacterial rot. The stored water in the leaves becomes a liability when the surrounding air is saturated, as the plant cannot properly regulate its moisture levels.
Second, most terrarium containers lack a drainage hole, trapping excess water within the substrate. When the soil stays wet for too long, the roots are deprived of oxygen, leading to eventual root rot. This process compromises the plant’s ability to absorb water and nutrients, resulting in a sudden decline and collapse.
Designing an Open Succulent Container
To successfully display succulents in a glass container, the structure must counteract the flaws of a traditional terrarium. The container must be an “open” design, featuring a wide mouth or a completely open top to ensure maximum air exchange and efficient moisture evaporation. This openness prevents humidity buildup and allows the soil surface to dry rapidly, mimicking the conditions succulents require.
Since the glass container will not have a drainage hole, establishing a robust drainage layer at the bottom is necessary to capture and separate excess water from the soil. This layer should consist of two inches or more of coarse material, such as gravel, pebbles, or lava rock. The volume of this layer provides a reservoir for water that percolates through the soil, preventing the roots from sitting in stagnant moisture.
A filter layer must be placed directly on top of the drainage material to maintain separation between the gravel and the succulent soil. This filter can be a thin piece of mesh, screen, or sheet moss. Its purpose is to prevent fine soil particles from sifting down and clogging the drainage layer over time. The visibility afforded by a clear container allows for monitoring the moisture level in the soil and the water accumulation in the drainage layer.
Essential Materials and Plant Selection
The foundation of a successful succulent container is the substrate, which must prioritize rapid drainage and aeration. Standard potting soil retains too much moisture and compacts easily, which is detrimental to succulent health. Use a specialized succulent or cactus mix, often created by incorporating inorganic materials like perlite, pumice, or coarse sand.
A reliable fast-draining substrate can be formulated by mixing one part potting soil with one part coarse sand and one part perlite or pumice. Pumice and perlite are porous aggregates that improve soil aeration and drainage, which is crucial for preventing root suffocation and rot. After planting, a top dressing of decorative gravel or sand is beneficial. This reduces contact between water and the base of the plant stem, minimizing the risk of rot and discouraging pests.
Plant selection should focus on small, slow-growing varieties that tolerate being contained and can handle slightly less than ideal conditions. Excellent choices include Haworthia, Gasteria, and various small Echeveria cultivars. These are naturally compact and can tolerate lower light or slightly higher humidity.
Highly sensitive species, such as Lithops, should be avoided, as they require specialized watering difficult to manage in a shared container. Watering must be infrequent and thorough, allowing the soil to dry out completely between applications.