The Ultimate Guide to a Closed Terrarium

Three terrariums
Three closed terrariums in jars

You have decided to build an eternal terrarium and not to buy it ready-made! Your motivation is high and you want to start right now. But you don't know exactly how to build such a closed terrarium. This ultimate guide will take you step by step from start to finish of your finished closed terrarium. Whether you just want to know a few little things, or just about everything.

I'll tell you about my experience with closed terrariums, from choosing your container to finally sealing and admiring your work of art in a jar. For all the more in-depth details and unanswered questions, I'll link you to other resources where you can get more information to make your closed terrarium great on the first try. 

If that's all a bit much for you, you can also reconsider and buy a closed terrarium.

In this ultimate guide I'm going to tell you whichmaterials you need for a closed terrarium and how to choose the best ones for it. After you have everything, we'll get to the actual construction. If you already know enough about closed terrariums, you can also just click right through this materials list here.

A shopping list for you

Here are all products for your closed terrarium summed up into an Amazon shopping list. You can buy them cheaply through the following links.

Which materials you'll definitely need for a closed terrarium

Affiliate note: I receive a small commission for some of the products linked in this article, if you buy them through my links. This won't cost you any more than usual! I recommend all of these products based on my honest opinion and not because of the commission I receive. As an Amazon Affiliate I earn through qualified sales. For more information, please read this affiliate note.


The following materials you will not get around in any case, no matter what your closed terrarium will look like later. What choices you have, I explain below. The following links will give you more information. But you can also continue reading this guide for your closed terrarium. 

Plants and animals are all inclusive

You don't have to put plants and animals in yourself. If you take soil from the garden or forest for your substrate, you certainly already have some with you. You can learn more about animals here. Now then, let's get started!

#1 Choosing your container

Glass containers with screw caps
Glass containers with screw caps. Source: pxfuel.com

In principle, there are no limits when choosing a container for your closed terrarium. Whether large or small. Closed terrariums can take any shape you can imagine, as long as you find a suitable glass for it.

Glass is also the decisive keyword at this point. From a chemical point of view, glass reacts with virtually nothing at all. At least with nothing that will be in your closed terrarium. It itself will forever remain as transparent as on the first day, although deposits can of course form on the inside.

Here are some beautiful container ideas for your closed terrarium.

Avoid plastic if you can

In principle you could also use a plastic container for your closed terrarium. But it's not as see-through as glass and will absorb some of the plants' green color over a long time. If you ever kept tomato sauce in plastic containers, you'll know what I'm talking about. If you ever plan on opening up your closed terrarium to clean or completely rebuild it, glass will be much easier to clean.

Also, if you ever want to open your terrarium to clean it or build a completely new one from it, you can clean glass much easier than plastic. 

#2 A false bottom for your plant's well-being

A false bottom in a closed terrarium
A false bottom in a closed terrarium

Next, you need to decide on a false bottom. You need it so that your plants don't stay under water for too long and drown. It also helps with general water distribution. I explain exactly how such a false bottom works in a different article.

Specifically, it consists of a cushion and a partition. Now you really only have to think about whether you want to use tropical plants or plants native to here.

Do you want native or tropical plants for your closed terrarium?

If you want to use native plants for your closed terrarium (or ones that generally don't need much water, like succulents), you can choose from pebbles, broken porcelain, broken glass, or even plastic balls for your cushion. 

Or some tropical plants?

If you prefer to use tropical plants, or generally those that require a lot of water, you should choose material that absorbs water.

There puffed clay balls offer themselves wonderfully. However, you have to be careful here that you can use them to reach a larger amount of water in your closed terrarium (but then you can't really see it at all) and possibly not notice that your plants are slowly but surely drowning. You don't have to worry about watering for the time being. 

Carnivorous plants and bonsais

Carnivorous plants as well as bonsais can be fitting plants for a closed terrarium. If you want to keep venus fly traps, sundew or pitcher plants, read this article. If you'd rather keep a small bonsai, read this article here.

Active carbon saves the day!

Interesting at this point is still coal, or activated carbon. This helps bind toxins in your terrarium, protecting your plants. Among other things, this prevents mold, which could completely destroy the ecosystem in your closed terrarium. 

I would not use activated charcoal as the only cushioning material, but always mix it with something else. Alternatively, you can also use charcoal, which does not have quite the same effect, but which you probably even already have at home. 

#3 A partition for your false bottom

Fly screen
Fly screen works really well as a partitioning wall. Source: sandid, pixabay.com

Lastly, you'll need the partition between your substrate and the cushion below. For this you can use dried moss, which will decay over time and become part of the substrate. A better option (which I also prefer to use) is a grid, such as a fly screen.

You can cut it from a roll and hide it under your substrate. The only important thing is that it can not rust. Most fly screens are made of fiberglass or other plastics anyway, so you don't really need to worry about it. Felt also makes a good partition. 

#4 The substrate your plants will anker their roots in

Your actual substrate will sit ontop of your false bottom, serving as a breeding ground for plants and animals alike. It largely depends on which kinds of plants you want to have in your closed terrarium. Your best choice will most often be soil from your garden or a nearby forest. It it important, however, that it cannot compact, or else water won't be able to flow through it anymore. You can read how to mix a good substrate here. Many more ideas are over on TerrariumTribe.

A springy effect

Every day, water from the glass panes and the leaves will fall back onto the substrate, flowing through it and dragging some soil with it, so that it becomes firmer and firmer in the long run. Those who still pour their own coffee through a coffee filter already know what I'm talking about.

The firmer your substrate becomes, the harder it will be for your plants to grow their roots there. Also, water will not drain as well and in the worst case drown your plants.

Therefore, it is important that you enrich your substrate with fibers that have a little spring. Again, dried peat moss is conceivable, but also coconut fibers or reeds, for example. You can mix your mixture approximately in a 2:1 ratio of soil to moss/coconut fibers/reeds. An exact ratio isn't important. Just estimate the right amount. 

If your closed terrarium is a little larger, you can also add earth worms. They'll loosen the soil day by day by digging their small tunnels through it. But please ensure that there is enough plants and dead plant material for them to eat! We'll look at some other animals soon. 

#5 Time for your residents!

Still open terrarium
A still open terrarium. Source: piqsels.com

Once you have chosen your substrate, you can start thinking about the plants that your closed terrarium will house. Your closed terrarium will always be at about room temperature in your home, or even a little warmer after a long time in the sun. You will also have a higher but relatively constant humidity than outside. You can choose your plants accordingly.

In general, you can take anything that sprouts in your garden in spring and summer. In my first terrarium, I put in a wild strawberry plant, various moss and weeds, an acorn and two ivy branches.

The ivy branches were actually intended as biomass and should decompose. I was very surprised when new roots and leaves suddenly grew from them.  

Moss, the all-rounder

You really can't do anything wrong with moss. It will grow just about anywhere, however the conditions in your closed terrarium might be. I recommend you read the article about moss. When choosing plants for your closed terrarium, please don't be too focused on a single type of plant. It could one day be suppressed by another plant and disappear completely.

You can read all about different plants for your closed terrarium in this article here.

Insects add some movement

Before you can finally start, you can think about some animals to live in your closed terrarium. This, however, will probably be your least concern. If you don't want any specific animals, you can skip this part. 

Depending on the size of your closed terrarium, you might not be able to add some types of animals. Please keep in mind that they're conscious beings that shouldn't suffer from living in a closed ecosystem for the rest of their lives. 

Beetles, worms and slugs

Different kinds of springtails
Springtails. Source: AJC1 at Wikimedia Commons, CC-BY SA 2.0

Springtails can always be used. They live practically everwhere and it'll be harder not to have them in your closed terrarium if you're using soil from outside. These small guys eat dead plants and turn them into new nutrients for your plants. They'll help your ecosystem a whole lot.

You can buy springtails online or cultivate them yourself quite easily. Other useful animals are beetles, isopods or snails. Keep in mind that your closed terrarium should be big enough!

#6 Time to build your closed terrarium!

Time for a cleaning session

Now we come to the actual construction for your closed terrarium. In the best case you have all your materials together now. To avoid unwanted germs in your terrarium, you should first clean your container.

It is best to use boiling water so that no germs remain in your container. Alternatively, you can use soap and warm water. Wipe your window from the inside and then rinse it again thoroughly with water only, so that no soap residues stick to the window.

Then dry it with a cloth. You can also use a paper towel, but then small pieces of paper may stick to the glass. For particularly small containers that you cannot reach with one hand, you can use pipe cleaners or roll up your cloth as tightly as possible.

Alternatively, you can use a dry eyeglass cleaning cloth and hold it with long tweezers. For more tips on how to clean your closed terrarium, see here.

Add the false bottom first

A false bottom in a closed terrarium
A false bottom in a closed terrarium

Once your jar is clean on the inside, fill it with the padding of your double bottom. This should be about 10 to 20% of the total height. It doesn't matter if it's a little off, though. Make sure your material is evenly distributed before placing your divider over it.

If you are using a grid or felt, the best way to cut it is to use a carpet knife. Compared to scissors, this has the advantage that you can easily trace the outline of your terrarium. Lay your grid flat on your cushion. 

Put your substrate ontop

Place the substrate loosely on your partition. You should not press it down. The plants and the constant water circulation will make it a little firmer over time anyway. You should fill in so much substrate that it is at least twice as thick as your false bottom.

The more substrate you put in, the better your plants can root and your animals can root around in it. Most plants don't really need more than 10 to 16cm depth and will do well with less.

My first terrarium has a depth of just under 4cm and the strawberry plants are still doing great after several months.

Hardscaping: let your imagination run wild

After you put in your substrate, you can start what is called hardscaping. 

Hardscaping means placing stones or other decorative elements into your terrarium. You could, for example, use those to implement different looking sections in your closed terrarium. Elevations can be very interesting. If you plan on looking at your closed terrarium from a single perspective, they can give a sense of more depth and make it seem larger than it really is. Elevations can be formed by natural, linearly rising slopes or by terraces. Stones are quite helpful to give your substrate a little more stability. Without them your substrate would get leveled by the water over time. 

For hardscaping, you can basically use all decorative materials that cannot rust or rot. Certain plants also do not tolerate lime. So if you want to use shells, find out about your plants beforehand.

Plant your plants

Now you can put your plants into your closed terrarium. Moss can easily be placed on top of your substrate and it will grow down over time. For plants with longer roots, you can make a small depression in your substrate, carefully place them in and add some substrate on top.

If you want to fix a plant in a certain position, you can tie it to something else. This can be, for example, a stick or another plant. It usually doesn't take long for them to hold themselves there on their own. You can either use twine to tie them down, which you will have to get out later, or you can use a trick.

As a substitute, longer blades of grass are suitable. Leaves of grass will fall off by themselves after a few days and decompose after some time. This way you don't have to open your terrarium again. 

It won't work without water

If you are satisfied with the appearance of your terrarium, you can now water it. This is unfortunately quite a tricky business. Because of your false bottom you don't have to be quite so precise, but some caution is still required here. Depending on the size of your terrarium, the amount will vary.

If your substrate is already moist, a few bottle caps of water may be enough. If, on the other hand, your substrate is completely dry, you should at least wet the entire surface once. I explain what you can do if you have too much water in your terrarium in this article

Here, too, lime can become a problem. This is found in our tap water. To avoid this problem, use distilled water or simply rainwater.

Closing thoughts (literally)

Modeling clay as a lid
Modeling clay closing up my closed terrarium in a light bulb

Now you can finally close your closed terrarium and you are as good as done! It is important that your closure is watertight. If you have a screw cap with a sealing ring, this is already sufficient.

If instead you have a leaky cap or maybe even just a cork, you can stretch plastic wrap over the opening and then close the jar. If you don't use too much plastic wrap, it will hardly show in the end. Again, the best way to cut off the excess on the outside is with a box cutter. Just be careful not to scratch your glass in the process. 

For more tips and tricks on sealing closed terrariums, see here.

A place to gaze

Voilá! Your closed terrarium is ready! Now you just need a location where you can admire it. Lighting is an important factor here. You should choose a place that gets a few hours of light (preferably sunlight) every day, so that your plants get enough energy.

Note that your plants will face the sun for a long time. So if you put your terrarium in front of a window, after a few days your plants will all face there. You can counteract this by rotating it every few days. 

Optional: Use artificial lighting

Alternatively, you can think about lighting with LEDs for your closed terrarium. This works similar to sunlight if you use white LEDs.

Sunlight contains all the wavelengths that the human eye can see and provides a good combination of the wavelengths that plants need. Note that your monitor, for example, produces white light for you through red, green and blue LEDs, not white LEDs. There are also larger lamps that produce white-looking light in the same way. This causes plants to miss out on various wavelengths.

Instead of LEDs, you can also use halogen lamps, which, like white LEDs, give you a full spectrum. An important cornerstone of lighting is power. Many lamps are simply not bright enough to provide a plant with sufficient light. 

Luckily, there are already special grow lights for plants that you don't have to worry about wavelengths and power. You can learn more about lighting here.

Need a refreshment?

If you've finished building your closed terrarium and want to clean it after a while, I recommend you read this article.

Are you done?

Now you know all the basics about closed terrariums for now! When you've made yours, feel free to send me a picture to jan@terrarium.blog or on Instagram to @terrarium.blog. I'll post the best pictures on Instagram and of course I'll be happy to link your profile! 

If you have any unanswered questions, write a comment under this post and I'll try to answer it as best as I can!

1 thought on “Die ultimative Anleitung für ein ewiges Terrarium”

  1. Ich muss sagen, ich bin begeistert!
    Ich hatte das Glück die Anleitung persönlich zu hören und habe mein eigenes Terrarium nach dieser gebaut.
    Seitdem beobachte ich täglich wie kleine Pflanzen wachsen und wie kleine Insekten den Boden erkunden. Das Glas ist Glühbirnen-förmig also sieht das Ganze auch noch schön aus!
    Lohnt sich und ist so pflegeleicht – perfekt wenn man nicht den grünsten Daumen hat!

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