A closed terrarium is a sealed glass container housing a self-sustaining miniature ecosystem. The sealed environment traps moisture, which cycles through evaporation and condensation to keep humidity consistently high; ideal for tropical plants such as mosses, ferns and Fittonia that would struggle in open air.
For most beginners, a sealed glass jar with moss and a small fern is the simplest and most reliable starting point.
Closed terrariums have become a popular way to bring low-maintenance greenery indoors. Their sealed environment creates a largely self-sustaining ecosystem, recycling moisture internally and requiring very little intervention once established. This makes them well-suited to anyone who wants a living display without the demands of conventional houseplants.
A closed terrarium is a sealed glass container that creates a self-sustaining growing environment. Inside, plants release moisture through transpiration, which condenses on the glass and returns to the soil, maintaining consistent humidity without regular watering.
How it works:
Benefits of closed terrariums:
Creating a closed terrarium involves selecting a suitable sealed container, choosing humidity-tolerant plants, and layering substrate materials correctly. Each layer serves a specific function: drainage, filtration, moisture retention and growing medium, and the order matters for long-term plant health.
Selecting the right container is essential for a closed terrarium. Using clear glass jars, vases, or cloches ensures good light penetration and maintains the required humidity levels. Examples include Mason jars, apothecary jars, or specialised terrarium containers. These containers should have enough space for the plants and design features, but not so large that the ecosystem becomes difficult to manage.
Choosing the right plants is critical to a closed terrarium’s success. Select small, slow-growing plants that thrive in humid environments. Ferns such as Maidenhair and button ferns thrive well, along with mosses like sheet and cushion moss. Tropical plants like Fittonia (nerve plant) and peperomia are also excellent choices. Avoid succulents and cacti, as they cannot tolerate the consistently high humidity inside a closed terrarium.
Creating a proper drainage system is vital. Start with a layer of gravel or small pebbles at the bottom of the container to support drainage. Next, add a thin layer of activated charcoal to help prevent odours and mould. Charcoal is essential for keeping your miniature landscape fresh. Keep each layer roughly one inch thick to maintain a balanced level of drainage and moisture retention.
Add a layer of moss to retain moisture and prevent the soil from sinking into the drainage layer. Sphagnum or sheet moss can be used for this purpose. Add a lightweight, nutrient-rich potting mix to create a stable growing base for the plants. Make sure the potting soil is rich yet light enough to allow roots to grow freely without becoming waterlogged.
Before placing plants into the terrarium, prepare them by gently removing excess soil from the roots. Arrange plants with taller varieties toward the back and smaller plants at the front to improve visual balance and light exposure. This arrangement enhances the aesthetic appeal and ensures each plant receives adequate light.
Carefully place each plant into the potting mix, ensuring the roots are fully supported. Use terrarium tools such as tongs or long tweezers to position plants without disturbing surrounding layers. This is also the stage to ensure plants are balanced visually and have enough space to grow without overcrowding.
Add decorative elements to personalise the terrarium and enhance visual appeal. Consider using small stones, crystals, or figurines. Driftwood or bark adds a natural touch. These elements not only enhance the aesthetic value but also help to create a themed terrarium like a fairy garden, jungle, or minimalist design. Choose elements that complement the plants and container for a cohesive look.
Lightly mist the plants and soil to initiate the terrarium’s internal water cycle. This kickstarts the water cycle within the closed terrarium. Seal the container tightly to maintain the high humidity required for closed terrarium plants to thrive. The mist creates an initial humidity level that is self-sustaining, as condensation will return moisture to the soil and plants. Ensuring a good seal also prevents external contaminants from entering the ecosystem.
For most beginners, a sealed glass jar with a layer of moss and one or two small ferns or Fittonia plants is the simplest and most reliable starting point. In our experience, the most common mistake is overwatering at the outset; once sealed, a closed terrarium needs far less water than most beginners expect. Mist lightly before sealing, monitor condensation on the glass over the first week, and open briefly if moisture appears excessive.
If moisture builds up significantly, open the lid for a few hours to allow excess humidity to escape before resealing. Beyond that, a well-built closed terrarium can remain largely self-sustaining for months or years with minimal intervention.
Miyagi Bonsai stocks a carefully chosen range of closed terrariums, glass containers and terrarium accessories, with next working day UK delivery available on most orders. The products and recommendations in this guide reflect what we stock, use and see working for our customers every day. We are rated 5 stars across over 100 Google reviews, and our team is on hand by email and phone if you have any questions about choosing or setting up your closed terrarium.
Common questions about making and caring for closed terrariums, answered.
Start with a clear glass container with a sealable lid to maintain high humidity. Layers include a drainage base (clay pebbles or gravel), activated charcoal to prevent fungus, a moisture-retentive substrate (peat moss, sphagnum, and potting soil), tropical plants, and decorative elements. Tools like tweezers help with planting.
Closed terrariums can last for years with minimal maintenance by creating a self-sustaining ecosystem. Moisture cycles within the sealed environment, reducing water loss. Occasional checks for mold or dead plants may be needed, but many closed terrariums thrive for 3-5 years or longer when well-balanced.
Build layered drainage, charcoal, and soil in a sealed glass container. Add tropical plants suitable for humid environments and carefully water the soil. Seal the lid to trap moisture, creating a mini water cycle where evaporation condenses and nourishes plants. Avoid overplanting to maintain balance.
Using just soil is not ideal for terrariums. Drainage materials like pebbles or clay balls are essential to prevent waterlogging and root rot. Proper layers support air, water, and nutrient balance crucial for healthy plants in a terrarium environment.
Yes, tap water can be used if free from harmful chemicals like chlorine. Let tap water sit for 24 hours to allow chlorine to evaporate. Alternatively, use filtered or distilled water for sensitive terrarium plants to avoid buildup of minerals or contaminants.
Choose slow-growing, tropical plants that thrive in high humidity and low airflow, such as ferns, mosses, fittonia, and small tropical vines. These plants help maintain oxygen and moisture cycles in the sealed environment.
Control moisture by adding appropriate water amounts when building the terrarium, sealing the lid tightly, and monitoring condensation. Wipe excess water droplets from glass to prevent mold growth, and open the lid occasionally if too much moisture builds.
Adding animals is possible but requires careful research. Small invertebrates like springtails can help control mold and waste. Larger animals need ventilation and meer space, which is usually limited in closed terrariums.
Clean your terrarium by removing dead leaves and wiping glass with a soft cloth. Use sterilized tools to prune plants and avoid harsh chemicals. Proper cleaning prevents pests, mold, and maintains plant health.
Place in bright, indirect light away from extreme heat or cold. Avoid direct sunlight, which can overheat and damage plants. A stable temperature between 18-24°C supports healthy plant growth and a balanced ecosystem.
