If you’ve been wanting to build a terrarium for a while, I have some good news for you: there are really only 5 basic components to a terrarium! Once you put these components together, your terrarium is pretty much good to go.
The 5 basic components of a terrarium are:
- The container
- The false bottom/drainage layer
- The separation layer
- The substrate
- Your plants
There are also some optional materials you may want to consider including:
Now, let’s get into what each of those layers are and what purpose they serve in your terrarium.
Table of Contents
The Terrarium Container and how to choose one
The container is going to be the main structure of your terrarium. Most containers are made of either plastic or glass.
The most important thing that you need from your container is transparency. Sunlight needs to be able to pass through the container so that your plants can absorb it for photosynthesis.
Keeping that in mind, most plastic or glass containers will work so long as they are transparent. So any spare containers you have lying around will work just fine.
The one thing I would advise against is using anything with stained glass. Stained glass will filter out a lot of the light, preventing your plants from benefiting from the full spectrum of visible light for photosynthesis. If you can, try to stick to clear plastic or glass containers.
The other factor you might want to consider when picking a container is the size and shape. Generally speaking, it’s going to be easier to work with a bigger container as well as give you more options when it comes to choosing your plants.
A larger container will also create a bigger buffer in the soil and air chemistry, meaning any problems that might come up with over/under watering, diseases, or mold growth will be milder and easier to deal with.
You also won’t need to have any special tools to handle your plants if your container is big enough to fit your hands in.
With that in mind, if you’re just starting out and want to experiment with terrarium building, a large plastic bin is the way to go.
If you do choose to work with a small container, just be aware that you may need to purchase some tools to reach in and handle your plants.
The False Bottom/drainage layer and what it does
The false bottom (also known as a drainage layer) is a layer of rocks or pebbles that allow water to drain away from the soil. It doesn’t magically provide your plants with any nutrients or healing powers, but simply creates space for water to drain away from the substrate.
In theory, you could get by without one, but I highly recommend including one especially for beginners who might not have a feel for when their terrarium is being overwatered.
There’s a number for benefits this provides:
- This prevents water from pooling around plant roots by facilitating drainage away from the soil, avoiding problems like root rot and mold.
- There’s a bigger buffer against over watering your terrarium
- It leaves space for water to accumulate, allowing for humidity levels to increase with the excess water in the system
The thing I like about the drainage layer is that it gives you a little bit of buffer against over-watering. If you have a drainage layer, excess water will simply collect at the bottom of the container, rather than drenching your plants and causing root rot and mold growth.
When you’re thinking about choosing the material for your false bottom, you have a lot of flexibility. For the most part, as long as you choose something that has a large and non-uniform (or spherical) shape, that’s going to naturally give space to allow water to pass through and collect.
So that could be anything from small rocks, marbles, gravel, or anything in between.
As for the thickness of this layer, you will generally want to aim for roughly one or two inches. Anything larger than that could allow for too much water to collect at the bottom, opening up the possibility of unwanted growth in the stagnated water.
You also want to keep this layer relatively small so that you have more space for the other layers and for your plants in your terrarium. Going too big will reduce the amount of free space you have to build your terrarium.
I have a full article on this that you can check out here if you want to learn more.
Separation Layer: function and requirements
The separation layer serves to keep your plant roots from reaching into the drainage layer while still allowing water to pass through.
This is important because if your roots are growing into the drainage layer where the water is pooling up, defeating the purpose of the drainage layer. That will lead to problems with root rot and mold growth.
It also helps to keep the soil from falling into and mixing with the drainage layer. If you want a very neat looking terrarium with very distinctive layers, that can be advantageous.
The main thing to keep in mind when choosing a separation material is how well it does at performing the jobs above. With that in mind, just ask yourself these two questions:
- Are the openings small/fine enough to prevent roots from passing through?
- Are the openings large enough for water to pass through?
If you can answer yes to those two questions, you will probably be good to use it as a separation layer.
If you want something that “just works”, you can use dried sphagnum moss or a synthetic mesh like the one here.
If you want to go the low budget route, you can use pretty much any thin, plastic bag you have laying around the house. All you would have to do is cut out a section and poke some holes into it to let water pass through.
Terrarium Substrate: which material works best
The soil is where your plants will be growing their roots and getting their nutrients. While there are a lot of options available to you, the soil you choose can influence how your plants will grow long-term and may be a contributor to some problems you might run into in the future.
Since the soil is where your plants are getting their nutrients, if the soil does not have nutrients to begin with, that will lead to plants with stunted growth.
If you’re not careful, there could also be chemicals, preservatives, or unwanted pests hitching a ride in your soil.
For the substrate you have a few options I’m going to recommend for you:
- Native soil
- Sphagnum moss
- Aquarium soil
Using native soil as your terrarium substrate
My go-to option is native soil. There’s a couple of reasons for this:
- It’s free
- It’s likely going to pair up well with any native plants you’re adding to your terrarium.
The only problem with using native soil is you can never be sure what’s going to be in there. It could be a carrier for rot, disease, or pests.
Despite this risk, if you’re seeing plants growing nearby supported by this soil, there’s a good chance the soil will support your terrarium plants just fine. However, it’s always a good idea to check what kind of soil your plant prefers if your plants are not native to your area.
If you want to be extra safe, you can always sterilize the soil by baking it at 350° for 30 minutes. This will get rid of any harmful organisms, weed seeds, and any other unwanted guests.
Using coir as your terrarium substrate
Coir is another option. It’s a fibrous material made from coconut husks. Usually they’re coming in the form of a block weighing a few pounds that will expand to a (much) larger volume when hydrated.
The advantage of using coir is it has really good water holding capacity while still having high porosity and drainage capabilities. It also doesn’t contain any pests since it’s pretty much man-made (from coconut fibers) rather than gathered from the wild.
The only difficulty with using coir is it doesn’t have any nutrients at all for your plants. If you are going to use coir, make sure to add a little bit of perlite in there for nutritional value. You might even be able to find some pre-made mixtures of perlite and coir online.
Using sphagnum moss as your terrarium substrate
Sphagnum moss is also a similar alternative to coir. It also has a pretty high water retention and will be pest resistant.
Like coir, it doesn’t have any nutrients. So you will want to make sure to add some perlite to get some nutrients in your substrate.
The only thing I would watch out for if you’re going to buy some sphagnum moss online is if there are any preservatives or dyes added. If you plan on having any living creatures in your terrarium, there’s a chance that could be harmful for their health.
Using aquarium soil as your terrarium substrate
Aquarium soil is another option available for you. It’s pretty much regular soil that’s been baked into these dry pellets. It comes with a lot of minerals because it uses volcanic granulates.
It’s a great way for your plants to get their nutrients without you having to add anything else into the soil.
Since it comes in the form of pellets, it’s also going to promote a lot of drainage in the substrate. That’s going to be very helpful to prevent root rot and mold growing around your plants.
The only thing to note is that the aesthetics of using pellets rather than traditional soil will not be suitable for everyone.
Terrarium Plants: rules of thumb for choosing your plants
Finally, to put the cherry on top, you have your plants. Your plants are literally the life of your terrarium.
When it comes to picking plants for your terrarium, there are some rules of thumb that you will want to stick to:
- Pick plants that can tolerate high humidity
- Choose plants that don’t grow too big
- Stick to plants that will tolerate low or indirect light
- Pick plants that share similar living requirements with each other
What you don’t want to do is throw any old plant into your terrarium and hope for the best. Not every plant is suitable for a terrarium environment.
If you want my quick top of the head recommendation, I would say ferns and moss will almost always be the to go to plants for any terrarium.
Ferns and moss love high humidity and generally don’t grow too big (with the exception of a number of species of ferns).
The other pretty safe option that you have is to gather plants found natively in your area (while sticking to the rules of thumb). Since these plants have already acclimated to your region, there’s a good chance that they will survive in your terrarium.
This is especially true for any moss or any plants that you see hiding in the shade. Typically, these types of plants will already be used to growing in an environment very similar to your terrarium.
If you choose to gather plants from your area, just be a little bit careful not to bring in any unwanted pests. For this reason, it’s helpful to give your plants a little soak in some water to help weed those pests out.
I have another article with my full list of plant recommendations that you can check out here. I go into a lot more detail on what specific plants will do best in most terrariums and what I like about them.
Charcoal (optional): what it does and why it’s helpful for your terrarium
Charcoal is an optional, but very helpful material you may want to consider adding to your terrarium either as the drainage layer or just above the drainage layer.
Charcoal helps prevent odors from developing in your terrarium. Its basic purpose is to filter the water that passes from the soil into the drainage layer.
Throughout the natural life cycle of a terrarium, you’ll eventually find dying indicating organic material. This is all natural, but this could lead to a buildup of harmful toxins that could negatively influence your plant health and could lead to the growth of mold.
Charcoal can help filter out these toxins by binding with the impurities before they have a chance to interact with your plants.
But before you go throwing your barbecue coals into your terrarium, you might want to check first to see if it’s the right kind to be used with plants.
You definitely want to avoid BBQ charcoal briquettes and charcoal used for stoves or fire pits. These will have a lot of harmful chemicals and microplastics that will be harmful to your plants.
If you’re looking for a safe charcoal to use, look for lumpwood charcoal or horticultural charcoal.
Sometimes when people refer to adding charcoal to a terrarium, they may be referring to activated charcoal. Activated carbon is different from regular charcoal in that it’s been processed to make it more porous. This treatment process allows the carbon to more readily bind with impurities.
Other types of charcoal you may come across might not have this characteristic. This may not be such a big deal, but just note that it may not be as effective as activated carbon, although they can be cheaper alternatives.
Springtails (optional): what they are and what they do
Springtails are another great (optional) addition to any terrarium. These are nearly microscopic, white-ish, gray insects that are commonly found in moist areas. If you have some, you might see them jump around a little bit.
They play an important role in cleaning up your terrarium by feeding on dead and decaying organic matter, fungi, and algae.
Adding springtails to terrarium will help greatly when it comes to avoiding mold growth in your terrarium. When combined with charcoal, they can tremendously help when it comes to keeping your terrarium clean and free of impurities.
You can get a starter kit by buying them online or you can culture your own. If you don’t have any yet, I would recommend buying a starter kit online and using that to create your own culture of springtails for future terrarium builds.
If you want to read more about springtails, check out this article here.
Decorations (optional): how to add some flare to your terrarium
If you want to take your terrariums to the next level, using decorations is the way to go.
Most decorations won’t influence the health of your terrarium, but they’ll do a great job at making your terrarium look more interesting. Pinterest has a lot of cool designs people have come up with.
The sky’s the limit when it comes to picking decorations for your terrarium. You can choose from all sorts of different knick knacks and figurines and various different techniques to create the look that you’re aiming for.
If you want to get some ideas of what you can use for decoration or things you might want to try out, check out this article here.
That’s it, that’s all the layers that go into a terrarium. If you’re looking into building a terrarium of your own, check out this article here.