The true meaning of terrarium is a closed environment – a few small plants growing in a transparent sealed container – its own little ecosystem.  Water inside the terrarium is constantly recycled.  When moisture from the air condenses on the glass walls of the terrarium, it is then returned to the soil and absorbed by the plants’ roots.

This type of terrarium is a great learning tool for children and adults alike.  Many different natural processes may be observed:  photosynthesis, respiration and water passing from liquid form to gas and back again.

When choosing plants for a closed terrarium, you will want to look for plants that love humidity; for example, small mosses, lichens and ferns.

Building your Closed Terrarium

1. Place a thin layer of small stones (approximately 1 inch) in the bottom of the terrarium to aid with drainage
2. Next place a thin layer (approximately 1/2 inch) of activated charcoal over the stones. It is best to use horticultural charcoal.  This acts as a filtration substrate and helps to keep the water clean
3. Next place a thin layer of sphagnum moss over the charcoal to act as a barrier to prevent settling of the soil
4. Place a layer of potting soil approximately 2 inches deep
5. Make small holes and carefully plant your chosen plants
6. Lightly mist with water the soil and sides of the container
7. Close up the container and you have a terrarium!

Care & Maintenance

The two factors that will most influence your success is sunlight and water.

• Sunlight: Be sure to place your terrarium in a bright area with indirect  Direct sunlight will most likely burn your plants
• Water: A properly maintained terrarium can go for weeks or even months without needing water.  Watch the condensation on the sides of the container to monitor watering needs.  If the sides are constantly wet, then you have too much water and will need to open the top to allow it to temporarily “dry out”.  You should see some mist on the sides of the container as well as a bit of fog.  If not, then it is time to give it a few shots of mist.
• Pruning: You will need to periodically prune your plants to keep them small enough to fit the container.  A small pair of scissors will work great for this.
• Fertilizer: You should not need to fertilize, as you want to keep the plants smallish.

Plants for High-Humidity Terrariums that enjoy moderate to dappled light

• Aluminum plant (Pilea cadierei)
• Arrowhead vine (Syngonium podophyllum)
• Artillery plant (Pilea microphylla)
• Asparagus or emerald fern (Protasparagus setaceus)
• Baby tears (Soleirolia soleirolii)
• Begonia rex (Begonia rex-cultorum)
• Bird's nest fern (Asplenium nidus)
• Black mondo grass

If you like succulents and cacti, then you can create stunning plantings in small glass containers, but these should only be thought of as short-term solutions for weddings, centerpieces, etc. 

Succulents and cacti should be watered thoroughly with adequate drainage where the soil is allowed to dry out between watering.  This cannot happen when the glass container has no drain hole.  Additionally, if you plant deep into a container with high walls, the humidity and condensation created by the glass walls will likely be detrimental.  Think of a desert and envision the air flow.

Succulents placed in a glass container with high walls will present a problem in that while the plants love the sun and even require it, placing a glass container in the sun will bake your plants! 

Air plants, on the other hand, work really well in the glass containers.  Most local nurseries will carry air plants and there are many online sellers as well.