Terrarium

What is Terrarium?

A terrarium is a transparent enclosure, typically made of glass, designed for keeping or raising plants or small terrestrial and semi-terrestrial animals indoors. These enclosures serve various purposes, including decoration, scientific observation, and the propagation of species.¹²

To function effectively, a terrarium aims to replicate a natural habitat by carefully controlling humidity, temperature, and ventilation. A covered terrarium can often sustain itself for extended periods by recycling moisture trapped inside. When used for plants, the base typically consists of a drainage layer of pebbles or sand mixed with charcoal, topped with a layer of soil. Common animal inhabitants include small reptiles, such as the red-eared turtle, or insects like ants. While a terrarium is designed for land-based life, it is often compared to an aquarium, which is intended for aquatic environments.²¹

What is the difference between an open and a closed terrarium?

The primary difference between an open and a closed terrarium lies in how they manage moisture and ventilation to replicate a natural habitat.

Closed Terrariums

A closed terrarium is covered, typically with a glass top, which creates a self-sustaining environment. Because the enclosure is sealed, moisture is trapped inside and recycled through a continuous cycle of evaporation and condensation. This allows the system to maintain high humidity levels for months without external intervention, making it ideal for tropical plants that thrive in damp conditions.²⁴

Open Terrariums

An open terrarium lacks a sealed top, allowing for constant air circulation and lower humidity levels. Because moisture can escape, these environments do not recycle water in the same way as closed systems. They are better suited for plants that prefer drier conditions or those that cannot tolerate the high humidity and stagnant air that can sometimes occur in a sealed container. Proper ventilation is essential in all terrarium designs to ensure the health of the inhabitants, whether they are plants or small animals.⁴

How does the water cycle work inside a sealed terrarium?

Inside a sealed terrarium, the water cycle functions as a self-contained, closed system that mimics natural hydrologic processes. Because the container is sealed, water is continuously recycled rather than lost to the external environment.⁵

The process relies on two primary mechanisms:

• Evapotranspiration: Plants within the terrarium draw moisture from the soil through their roots. This water travels through the plant and is released into the air as water vapour through the stomata of their leaves, a process known as transpiration. Simultaneously, water evaporates directly from the surface of the soil.⁵⁶
• Condensation and Precipitation: As the air inside the sealed container becomes saturated with water vapour, it eventually reaches its dew point. The vapour condenses into liquid water droplets on the cooler surfaces of the glass walls. Once these droplets accumulate and become heavy enough, they run down the sides of the container or drip from the lid, returning to the soil as a form of internal precipitation.⁵

This cycle allows the terrarium to maintain a consistent level of humidity, effectively sustaining the plants with minimal external input.⁵

What are the best types of plants for a low-maintenance terrarium?

For a low-maintenance terrarium, the best plant choices depend on the temperature and environment you intend to create. Selecting species that thrive in similar conditions ensures the system remains stable with minimal intervention.

Recommended Plants by Environment

• Cool-Temperature Terrariums: If you prefer a cooler setup, consider using mosses, lichens, wood ferns, violets, trailing arbutus, or anemones.⁴
• Warm-Temperature Terrariums: For warmer, more tropical environments, popular and resilient choices include begonias, croton, peperomia, creeping fig, selaginella, Dracaena sanderiana, Chinese evergreen (Aglaonema), and maidenhair fern.²

To ensure your terrarium remains low-maintenance, it is essential to establish a proper foundation. A base layer of sand or large pebbles mixed with a small amount of charcoal, topped with 2–3 centimetres of soil, helps manage drainage and prevents root rot, which is critical for long-term plant health.⁴