Updated/Fact-Chacked on June 1, 2023 by Gareth James
After building my whisky barrel pond last year, I have enjoyed watching this mini-ecosystem thrive. I wanted to create and self-contained ecosystem indoors and then stumbled across terrariums. I was instantly captivated. Some of the
This article outlines the process I used to create a closed terrarium after hours of research, along with a lot of trial and error and testing products I bought online.
I have recently updated this article showing how my terrarium looks after 16 months and discussed some of the problems I have encountered.
What is a Closed Terrarium?
A closed terrarium is a complete mini-ecosystem in a bottle or jar (usually a glass storage jar). Closed terrariums can be entirely self-sufficient if set up correctly; some have not been opened for decades and are still thriving today.
The closed terrarium water cycle mimics that found in nature. Once water is added to the terrarium and the lid closed, it becomes continually recycled. Water droplets form inside the glass container due to condensation and the plants giving off water through their pores (stomates) during photosynthesis. Water then runs down the jar into the soil, and the process repeats.
The plants in a closed terrarium also produce oxygen as a by-product of photosynthesis; this is why many closed terrariums can also support small insects and isopods. This process is reversed at nighttime, allowing plants to get CO2 for photosynthesis; the plants can also absorb carbon from the soil as old leaves and organic matter decay.
What You Will Need to Build a Closed Terrarium
All the items below can be bought from Amazon and Etsy, I found Etsy is best for buying plants with a few dedicated sellers. I have included links to the items I purchased (these are affiliate links, and I will get a tiny commission if you buy the items).
- A glass bottle or container (Amazon)
- Gravel for the base (Aquarium gravel from pet local pet shop)
- Mesh (optional via Amazon)
- Substrate/Soil (Etsy but you can buy in a local plant shop)
- Activated charcoal (Amazon)
- Plants (Etsy)
- Terrarium building tools (Optional, Amazon)
- Decorative items e.g. wood, moss, ornaments
You can get many of these items in a closed terrarium starter pack like this one (plants, soil, sphagnum moss, charcoal, pebbles, black orchid) – this might be easier to start as it’s a pain buying everything separately. I opted to buy everything separately, as I was going to build a few terrariums and needed larger quantities of each item.
Choosing Your Container for Your Closed Terrarium
Any glass bottle or jar can be used to make a closed glass terrarium; it just needs to be airtight. Screw-top jars or jars with clip lids work well, I opted for a 4 litre Kilner jar with stopper-lid from Amazon.
If you use a bottle with a neck, you will need to buy some long implements to move the plants and soil into position. My next terrarium will be in an antique bottle so that it will be tricky to plant through the narrow neck.
These types of cases are named after Nathaniel Ward (1791-1868), who pioneered the transportation of plants in glass cases with his book ‘On the Growth of Plants in Closely Glazed Cases’ in 1842. During the colonial years, many plants would die when shipped over to Europe from around the world; Wardian case terrariums provided the ecosystem with each plant needed to survive transportation.
Steps to Build a Closed Terrarium
Step 1: Check you have all of the above items.
You don’t want to get halfway into this project to discover you are missing an item.
Step 2: Build a false bottom
I have watched many videos on youtube of people experimenting with different setups. The best channel, Serpadesign, recommends using a ‘false bottom’. Often called a riparian layer, the false bottom is the key to building your water cycle. The false bottom consists of a layer of stones separated by a mesh barrier that divides it from the substrate.
If they are not separated, soil can enter the base of the jar and sit in water, making it putrid and rotten – this would affect the whole ecosystem.
For the mesh barrier, a carbon fibre window screen is a good option (see list above for link). You have to buy a roll and cut it to the size of your closed glass container.
Add your gravel to the bottom of your bottle and sit your cut mesh barrier on top. For the stones, I used aquarium gravel to add some colour. You can use sand, but the evaporation is not as good.
Step 3: Add your activated charcoal
Activated charcoal is created by heating organic matter, like wood, and can be bought online or in stores. Activated charcoal absorbs toxins, which is why it is often used in ERs to treat overdoses. Within a closed terrarium environment, activated charcoal helps prevent mould and stops your plant roots from rotting.
As the activated charcoal forms a complete layer, it also cleans the water as it passes through to the false bottom layer. I also added some to by false bottom layer to help clean any water that may sit on the base.
Step 4: Add the substrate layer (Soil)
The substrate you use will depend on what you wish to plant. If you want to add tropical plants to your terrarium, like succulents, it’s best to use a tropical soil mix that can be purchased online – otherwise, general house plant soil will be adequate.
You can make up your tropical substrate mix using: a soil base like potting soil, bark that has not been dyed, sphagnum moss, and horticultural sand/grit.
Add the same amount of substrate to your bottle as you did stones, so you get nice layers. The substrate needs to be deep enough actually to plant the roots, so don’t be too sparing. This is where I initially went wrong.
If you create a native terrarium with plants from your local area, you can use the soil the plants were growing in. Serpadesign recommends baking the soil first to get rid of any parasites, but I will try the natural approach for my second terrarium build.
Step 5: Add Plants
When choosing your plants, you can either go for tropical plants or native plants local to you.
Best closed terrarium plants include Polka dot plants, Peperomia, Miniature English ivy, ferns, and mosses.
Dig a small hole in the substrate and use a tool to carefully place the plant in the hole and cover up the roots.
Below is my completed terrarium. I added a small buddha which totally changes it from ‘plants in a jar’, to a scene.
Closed Terrarium Tips for Success
– Don’t overwater, especially if you are not using a false bottom.
– Water the terrarium by gently spraying down the sides of the jar and letting it naturally run into the soil.
– Think of building a scene, like a Mayan jungle setting. Mine totally changed once I added my Buddha figure.
– Add some other bits you come across to make it visually appealing. I added a piece of driftwood to separate the foreground/background. I also added a large piece of slate to try and resemble a rocky mountain and some sea glass.
Closed Terrarium Maintenance & Problems
Once your closed glass terrarium is set up, it could last years without being opened; the one below was created in the 60s by David Latimer and was last opened in 1972!
Getting the perfect setup may take a few tries to get right. If you see too much condensation building up on the inside and not clearing, simply remove the lid for an hour. You may also find your terrarium getting misty, but this soon clears.
While your terrarium is settling in, check the soil for moisture every week. Stick your finger into the substrate to test for dampness, if it’s totally dry, add some water.
My Closed Terrarium 2023 Update
My meditating Buddha has been lost in his jungle! Roots have grown up the sides of the terrarium on the window side of the container.
I have been taking the lid off occasionally to either wipe excess moisture off the glass or to add water when things look too dry. Sometimes the terrarium is full of condensation for days, and you can’t see anything.
I think at this stage, I need to start trimming everything back, but not entirely sure what to do with the roots (and algae) on the other side. It looks hideous.
Closed Terrarium FAQs
Do closed terrariums need air?
No, they can thrive perfectly well in a closed container with the correct setup.
Do you need charcoal in a closed terrarium?
Ideally yes, activated charcoal helps keep the terrarium clean and free of toxins.
How long can a closed terrarium last?
Years, the oldest terrarium is over 60 years old and never opened.
Do closed terrariums need sunlight?
Yes, they will need some sunlight for plants to make food by photosynthesis.
Can I use BBQ charcoal for a terrarium?
No, BBQ charcoal is full of nasty chemicals. Look for pure activated charcoal.
Can you use activated charcoal powder in a terrarium?
This is more for human consumption, sold as supplements. You really want large chucks as they will help to filter your water.
How much light should a closed terrarium get?
The plants will need at least 2 hours per day of sunlight, but you don’t need to add direct sunlight. My plants are thriving in a north-facing window.
How much water should I put in a closed terrarium?
Add enough to dampen the plants and soil (around 5-8 mist sprays) then check the soil weekly.
How often should I mist my terrarium?
You will only need to mist your closed terrarium again if the soil feels dry.
Do succulents do well in a closed terrarium?
No, succulents prefer open terrariums, they don’t do well in a sealed terrarium. Consider buying a fishbowl type setup.
Can you open a sealed terrarium?
Yes, you can open it regularly to make sure the soil is damp enough and to move things around.
What is the difference between charcoal and activated charcoal?
Activated charcoal has been heated.
Can you put lights in a terrarium?
Yes, you can create a more elaborate setup with lights, this will also give you more options for plants.
What animals can live in a closed terrarium?
Isopods like woodlice and worms can thrive in a closed terrarium. They will become part of the ecosystem producing waste that will get broken down to feed the plants.
How do closed terrariums get carbon dioxide?
The terrarium plants will produce CO2 during the night.
Why are my plants dying in my terrarium?
The most common reason is lack of moisture.
What plants can I put in a terrarium?
Small house plants work best, but make sure you buy miniature versions e.g. Polka dot plants, Peperomia Miniature, Miniature English ivy
Why does my terrarium fog up?
This is perfectly natural, it’s just condensation building up which will clear in a few hours
What’s the difference between a vivarium and a terrarium?
Terrariums are made for plants, while vivariums are built to house animals, though both may have the same environments.
Can I put a jade plant in a terrarium?
Jade plants do well in closed terrariums, if you are asking about jade stones, these can also be placed in your terrarium to add colour.
Can worms survive in a closed terrarium?
Yes, worms can serve in a closed terrarium with the correct setup, these can be used in terrariums built from local habitats.
What bugs can go in a terrarium?
Isopods can thrive in closed terrariums.
Does a closed terrarium need air holes?
No, the plants create oxygen in the terrarium.
Should you remove dead leaves from the terrarium?
No, these ideas leaves will be broken down over time and provide essential nutrients to your plants.
Gareth is the owner of Plantsman Media. Gareth lives in the North East of England and is obsessed with flowers. He has just started RHS level 2 certification.