Terrarium Layers: Our Top 5 Soil Mixes + How to Layer a Closed Terrarium (Guide)
Hello, friends!
Today we will be unearthing the secrets of terrarium layers.
What are they?
What order do they go in?
What’s the best soil mix, and how do I make it?
All these questions and many more will be answered in this deep-dive guide as we will get to the core of every question.
Terrariums are self-sustaining ecosystems made atop a series of substrate layers
I’ve been making terrariums for years and I am constantly refining and perfecting my recipes. I understand how important it is to feel like you know what you’re doing when making a terrarium.
You don’t want to leave things up to chance.
It is crucial to get your terrarium layers in order and soil mixture correct, why?
- To enable proper drainage to protect your plants from root rot
- To filter out any harmful chemicals or compounds inside your closed terrarium.
- To allow for proper water retention – keep your tropical plants hydrated.
- To balance nutrition availability and nutrient delivery – promoting healthy yet controlled growth
- To elevate your designs, e.g. the use of decorative sand layers or terrarium putty
- To enable an active water cycle
So, grab a shovel and let’s dig in.
Quick Guide
1. What Are Terrarium Layers and What Order Do They Go In?
This guide will most specifically discuss closed terrarium layers – this means tropical/sealed terrariums.
Layering a terrarium is more straightforward than it may first appear, and you don’t need loads of materials.
In fact, our essential recipe for terrarium layering only includes three components.
LECA is the foundational and second-most essential terrarium layer - used for drainage.
I will first explain to you the basics and what we use – and then we will discuss any and all extras you might want to consider.
Remember, for a more complete guide to terrariums - check out our beginner's guide.
So, what are the terrarium layers and how do I set up my terrarium?
- Layer 1: Drainage – we recommend using LECA
- Layer 2: Filtration – we recommend using Activated Charcoal
- Layer 3: Substrate – we recommend using a classic Terrarium Substrate Mix.
1.1 The Three Essential Layers of a Terrarium
Layer 1: The Drainage Layer
Terrariums are closed ecosystems – meaning they are highly susceptible to overwatering.
If you have poured any more water than is needed it will sit in the substrate/soil layer and your plants will eventually succumb to root rot.
That is unless you have a drainage layer.
Drainage is your very first terrarium layer and is usually made up of some sort of gravel, sand or stone and serves to allow excess water to drain through the soil layer away from the roots of your plants.
For your tropical terrariums we always use, and recommend you use LECA; lightweight expanding clay aggregate, otherwise known as hydroton clay pebbles.
There are several advantages to using LECA over other drainage mediums:
- It’s lightweight thus protecting your glassware from breakage
- It’s durable and resistant to physical pressure (so much so it’s often used in the construction industry)
- It is water absorptive – a LECA setup can therefore wick water back up to your plant roots if they need it
- It’s affordable, unlike certain processed aquarium sands
- It’s sustainable and undyed
- It comes sterile – you have no risk of mould/bacterial build-up
How much drainage should I put in my terrarium?
It does depend on the size of your terrarium container, but I would generally recommend a layer about half an inch thick up your container.
To give an example, for a 2L container we would use about 300ml of LECA.
For a 10L container, we would use about 900ml of LECA.
Where to buy LECA
UK: Shop LECA with ome
USA: Shop LECA on Etsy
Activated charcoal or activated carbon comes in many forms - including pellets, flakes and powder.
Layer 2: The Filtration Layer
Your second terrarium layer, the filtration layer, has the role of protecting your ecosystem from chemicals and compounds that could harm your plants and moss.
The undisputed queen of filtration is activated charcoal.
Activated charcoal is charcoal that has been treated at extremely high temperatures giving it a massive, porous surface area.
This surface makes it the perfect filter – it can adsorb impurities in your terrarium, such as:
- Pesticides
- Herbicides
- Organic compounds such as benzene, toluene and formaldehyde.
- Chlorine
- Bacterial toxins.
Some argue that a charcoal layer is not ‘essential’ and, arguably, you could probably get away without it.
But, we’ve made thousands of healthy terrariums and they’ve all included activated charcoal – with that in mind we’re not about to drop it from our classic recipe.
The charcoal we use, and supply is environmentally friendly – made from sustainable plant resources and is non-polluting.
Alternatively, you could use BBQ charcoal – however, these are not as effective as filters and are less environmentally friendly, as often other chemicals are used in their production.
How much charcoal should I put in my terrarium?
You could use charcoal as another ingredient in your terrarium substrate mix.
However, I like to use it as a separate layer entirely to further increase the barrier between your roots and any water deposits.
Sprinkle a thin layer of activated charcoal on top of your LECA layer – enough just to cover the layer.
Where to buy Activated Charcoal
UK: Shop Activated Charcoal with ome
USA: Shop Activated Charcoal on Etsy
What our essential combination looks like from outside the glassware
Layer 3: The Substrate Layer
Your soil mix is arguably the most important component when it comes to terrarium layering.
For a closed terrarium you will need a substrate mix suitable for tropical plants.
It must be well-draining yet water retentive.
It must promote aeration within itself and have a healthy mixture of nutrition and mycelium.
Not asking much, huh?
I would generally recommend avoiding standard potting mixes or garden soil – but if you’ve got nothing else – go for it.
Don’t worry – down below we’ve detailed our classic tropical closed terrarium substrate mix.
Make sure to gently compress your substrate layer once placed inside your terrarium.
We also recommend lightly misting your substrate layer at this stage to make it more malleable for your hardscape and plants.
Other soil mixes
Different terrariums may require different substrates. For example, you might need a more putty-like terrarium mix that can easily adhere to your container, allowing you to build vertical moss walls.
Or you may be constructing an arid open terrarium using cacti and succulents. In which case you would need more of a desert mix.
You can find all our substrate mix recipes down below in this article.
How much soil should I put in my terrarium?
You will need more of your soil mix than either of the other two layers.
What plants you use, and how big they are, will determine how much of your soil mix you will need. Typically, around 1/4th of your glassware should be taken up by substrate.
If you’re just using plant cuttings rather than full plugs – you can get away with less substrate.
If you’re using larger houseplants, you’ll need more substrate.
To give you a more specific example, for a 2L container we would use about 600ml of substrate mix.
For a 10L container, we would use around 1800ml of substrate.
And so, you see, layering a terrarium is quite simple, so long as you have the right materials to begin with.
Where to Buy Terrarium Soil
UK: Shop Terrarium Soil with ome
USA: Shop Terrarium Soil on Etsy
1.2 Additional Terrarium Layers
Sphagnum moss can be used as its own layer, mixed in with the soil or used as a top-level decoration.
Sphagnum Moss Layer
Sphagnum moss is a type of peat moss that is widely found in damp, boggy regions across the Northern Hemisphere and is known for its unique water retention capabilities.
It has a soft, spongy texture and a distinct, light green colour, often turning brown as it ages or dries out.
This layer is usually sandwiched in-between the filtration layer and the substrate layer.
Why use Sphagnum moss?
- Moisture Regulation: Sphagnum moss can absorb and retain a significant amount of water (up to 20 times its dry weight), which helps maintain humidity levels within a terrarium.
- Acidity Control: Sphagnum moss naturally has an acidic pH, which can influence the soil composition and is beneficial for growing acidophilic plants such as various species of moss.
- Antibacterial Properties: Sphagnum moss contains phenolic compounds that provide antibacterial benefits, reducing the growth of harmful microbes and promoting a healthier terrarium environment.
Now I know what you’re thinking.
Isn’t this the same as peat moss? Isn’t that bad for the environment?
Not exactly.
Peat moss is sphagnum moss that has died, decomposed and accumulated under the surface and at the bottom of bogs over periods of hundreds and thousands of years.
Peat moss is removed by entire bogs being drained and is thus a highly unsustainable substrate component – despite how effective it is.
Sphagnum moss on the other hand is the live moss that resides on the surface of bogs and regenerates much more quickly.
How much sphagnum should I put in my terrarium?
Just enough to cover your activated charcoal layer. I usually place sphagnum moss in a ‘clump’ in the centre of my layers – as I don’t like how it looks from the outside of the terrarium.
Where to Buy Sphagnum Moss
UK: Shop Sphagnum Moss with ome
USA: Shop Sphagnum Moss on Etsy
Sand can either be used as the drainage layer, or on top of your activated charcoal
Decorative Sand Layer
All of our layers so far have been fielded in favour of their function.
Now, we can talk about form.
Sand art inside glass containers is a thing in itself - however they can also be used to great effect in terrariums.
Sand layers can help break up the brown hues of your layering with something more striking and eye-catching.
You could use any colour of aquarium sand – but for a simple example let’s just use black and white sand.
First, we want clean and crisp lines. We don’t want our sand leaking into our other layers.
So, on top of your filtration layer pour a thin layer of black sand. Only on the outside of the layer (the rim) – it doesn’t need to cover the whole surface area.
We are using black sand to begin as it will be the same colour as activated charcoal and therefore the sand won’t visibly ‘bleed’ into the next layer.
Once you have a complete layer of black sand – you pour on a layer of white sand.
As the sand grains are of the same size, the white sand should sit neatly in a sharp line atop the black sand.
You can now repeat this series of steps as many times as you like and with whatever thickness of sand line you like.
You can, if you’re feeling fancy, create wiggles, waves or shapes within your sand art to make your terrarium stand out.
Where to Buy Terrarium Sand
UK: Shop Terrarium Sand on Etsy
USA: Shop Terrarium Sand on Etsy
Metal Mesh Layer
You don’t need a mesh layer.
One of the most common misconceptions is that it’s essential to have a metal mesh layer separating the drainage layer.
The idea is that you have a fine mesh material cut out into the shape of your container (across its x and z axis, so you have a flat cross-section) and place it above your drainage.
This layer is supposed to separate the drainage layer so that the substrate layer doesn’t ‘bleed’ into it – protecting the function of the drainage layer over time.
While in theory this makes sense, it is much more applicable for something like a vivarium build which will constantly have new water introduced into the ecosystem.
Within a terrarium, you will likely add water incredibly sparingly.
And so, over time, if your soil layer does indeed bleed into your drainage layer it doesn’t matter.
Each layer can be considered separately or taken as part of the whole.
If your terrarium manages to survive long enough for this bleeding to happen it means it isn’t overwatered.
And if your roots are reaching down below the substrate layer – it’s again a sign of a healthy terrarium.
A mesh layer is unlikely to prevent roots from reaching further down your container – and over such a long time there is really little benefit to having your drainage and substrate layers separated.
Additionally, the mesh layer never looks very good, either.
Yes – I know Serpadesign always uses a mesh layer – but this is a practice best reserved for vivariums, trust me!
Leaf litter is a great source of nutrition for your microfauna - make sure anything you use has been sterilised.
Sterilised Leaf Litter
A ‘bioactive terrarium’ is one in which microfauna (or mesofauna) are introduced.
These are living organisms in the animal kingdom which play a role in the functioning of the ecosystem.
Springtails, for example, are a common addition to tropical terrariums.
These detritivores help to break down decomposing organic matter which is in turn converted back into nutrients for the health of the flora.
Sterilised leaf litter is a source of nutrition for your microfauna.
Scrunch up a few handfuls and add it to your terrarium potting mix for a slow-release source of nutrition which can boost your microfauna population.
Where to buy Sterilised Leaf Litter
UK: Buy leaf litter on Etsy
USA: Buy leaf litter on Etsy
2. Terrarium Soil Recipes
I want to run you through a few different options for your terrarium substrate.
- For most closed terrariums, you just need our ‘terrarium substrate mix’.
- The ‘ABG’ mix is historically preferred as an all-rounder, however, isn’t environmentally friendly.
- We have made our own, more advanced, or even ‘ultimate’, terrarium substrate mix, to rival the ABG mix.
- Our Terrarium Putty mix creates a sticky, goo-like putty that allows you to create vertical moss walls and more intricate designs.
- Finally, the Desert Plants Mix is a substrate composition specifically designed for arid plants such as cacti and succulents, if creating open planters or ‘open terrariums’.
We use our classic terrarium substrate mix in the vast majority of our closed terrariums.
2.1 Classic Terrarium Substrate Mix
Ingredients
- 2 parts coco coir
- 2 parts orchid bark
- 1 part black sand
- 1 part worm castings
About the Terrarium Substrate Mix
Coco coir is a wonderful, eco-friendly alternative to peat moss. It is highly water-retentive and has a high cation exchange rate – meaning it is superbly effective and delivers nutrients to your plants.
Meanwhile, orchid bark and sand allow for drainage within the substrate mix. Without them, the active water cycle will slowly compress your soil until the water becomes trapped – and your plants begin to rot.
Additionally, these two additives allow your substrate to aerate, allowing oxygen to continuously reach the roots of your plants.
Finally, worm castings (vermicast) provide nutrition to your plants. Additionally, worm castings include mycelial deposits that can aid in breaking down decomposing organic matter to help protect your terrarium from mould.
Learn more about stopping mould development in your terrarium.
2.2 ABG Mix
Ingredients
- 2 parts orchid bark
- 2 parts Tree Fern Fibre
- 1 part sphagnum moss
- 1 part peat moss
- 1 part activated charcoal
About the ABG Mix
The ‘Atlanta Botanical Gardens’ Mix has been a terrarium staple for years.
In more recent years, however, the recipe has been dropped due to its containing both peat moss and tree fern fibre – two highly unsustainable components.
While I therefore cannot recommend this specific composition – it does highlight an interesting point.
You will notice that the activated charcoal and sphagnum moss are mixed into the substrate itself.
See our recipe below.
2.3 Ultimate Terrarium Substrate Mix
Ingredients
- 2 parts coco coir
- 2 parts orchid bark
- 1 part black sand
- 1 part worm castings
- 1 part sphagnum moss
- 1/2 part sterilised leaf litter
- 1 part activated charcoal
About the Ultimate Terrarium Mix
If you are combining all these components into one substrate, you need simply to have a LECA layer underneath.
Do make sure, as with any mix, that all of your parts are thoroughly combined before use.
Ok this looks kind of suspect. But, trust me, terrarium putty is a lifesaver.
2.4 Terrarium Putty Mix
Ingredients
- 2 parts coco coir
- 2 parts worm castings
- 1 part terrarium clay powder
- Add water to achieve the desired consistency
About Terrarium Putty
This mix has been much requested on our Instagram - and we’re finally releasing it.
After all that, it was quite simple really, wasn’t it?
I’m also happy to announce now have terrarium clay powder available in our online shop.
You can use this sticky terrarium putty to create solid, gravity-defying walls of substrate.
Alternatively, you can use it to rap around plant roots and stick whole plants to your hardscape.
Watch the video below for examples of both!
I usually don't recommend mixing succulents, cacti and terrariums...but if you have to, read on.
2.5 Desert Plants Mix
Ingredients
- 1 part coco coir
- 1 part worm castings
- 2 parts grit
- 2 parts perlite
About the Desert Plants Mix
I’ll be honest – I’m not an expert on Arid plants (yet) however, succulent and cactus terrarium layers are straightforward.
I have provided a simple alternative to the standard potting mix that would provide more ample drainage.
Arid plants don’t tend to fare well in terrariums. First, because they don’t enjoy humidity – and secondly because they need very strong drainage to allow any water to fully pass through the plant.
Planters with a drainage hole are thus ideal. Otherwise, you could simply beef up your LECA layer.
3. FAQs
What are the essential components for a basic terrarium soil mix?
We recommend:
- 2 parts coco coir (water retention and nutrient delivery)
- 2 parts orchid bark (aeration and drainage)
- 1 part worm castings (nutrition)
- 1 part black sand (aeration and drainage)
How does layer thickness affect plant growth in terrariums?
Layer thickness should be proportionate to the container size and plant type. Thick layers can limit your design, while too thin layers may not provide sufficient nutrients or moisture retention.
What is the best way to prevent soil from mixing into the drainage layer in a terrarium?
For a terrarium, you don’t need to worry about this. Mesh layers aren’t essential, but if you have to keep the layers separate you can use a sheet of mesh between the soil and drainage layers to prevent mixing.
Can you use charcoal briquettes as a substitute for activated charcoal in terrariums?
It is not recommended to use charcoal briquettes as they may contain additives harmful to plants and do not have the porosity required to effectively filter air and water like activated charcoal.
How do you properly sterilise the soil for a terrarium to prevent mould and pests?
If you’re using soil from your garden or outside, sterilise the soil by baking it in an oven at 200°F (about 90°C) for 30 minutes, or by microwaving moist soil on high for 2-3 minutes. Allow the soil to cool completely before use.
What role does the particle size of the substrate play in terrarium health?
Particle size affects drainage and aeration. Small particles can lead to compact soil that restricts airflow and water drainage, while larger particles improve aeration and drainage but may not hold moisture well. This is why we have a mix of large and small particles in our terrarium soil mix.
How often should terrarium soil be replaced or refreshed?
If you have a fully-functioning bioactive terrarium you shouldn’t need to replace soil. However, if you think your terrarium needs a top-up you can funnel in a new top layer of soil rich with nutrients as and when it might be required.
Is it possible to create a self-sustaining terrarium without any soil layer?
Technically, yes! You could, for example, use air plants atop a drainage layer for a complete terrarium look without the need for soil. But, this wouldn’t technically be a terrarium – as you would likely need to remove the air plants to water them.
What are the best practices for layering substrates in a desert-themed terrarium?
Use a well-draining mix dominated by sand and perlite, with a lower proportion of organic material, to mimic arid conditions. You can even lay sand on the top layer of the substrate to create a real desert aesthetic!
Do I need a drainage layer for my closed terrarium?
A false bottom creates a space between the drainage layer and the terrarium's actual bottom, allowing excess water to collect away from the plant roots, preventing waterlogging and root rot.
Should I use orchid bark in my substrate mix?
We do! Orchid bark increases aeration within the substrate and helps maintain appropriate moisture levels.
How can you use sphagnum moss effectively in terrarium layering?
Sphagnum moss can be used as a top layer to retain moisture and create a humid microclimate or mixed into the soil to improve moisture retention and acidity.
What are the environmental impacts of using peat in terrariums, and what are sustainable alternatives?
Peat extraction can damage ecosystems; sustainable alternatives include coco coir, rice husks, or recycled green waste. We recommend coco coir, all the way.
How do you adjust terrarium soil pH naturally?
To lower pH, add sphagnum moss or pine needles; to raise pH, incorporate crushed eggshells or small amounts of lime.
What substrate is best for carnivorous plants in terrariums?
Use a mix of sphagnum moss and sand in equal parts, avoiding nutrient-rich soils to mimic their natural, nutrient-poor habitat. Be warned; carnivorous plants don’t tend to fare well in closed terrariums.
Can kitchen scraps be composted directly in a terrarium?
It's not recommended to compost kitchen scraps directly in a terrarium as they can attract pests and cause odour issues. Instead, use pre-composted organic matter. Or, if feeding microfauna, use crushed and sterilised leaf litter
What considerations should be made for terrariums designed for reptiles or amphibians?
Substrates for these terrariums must be non-toxic, easy to clean, and capable of maintaining the necessary humidity and temperature conditions specific to the species. Thoroughly research the specific requirements for whatever creatures you add to your vivariums and terrariums.
How can you effectively layer a terrarium for aquatic plants?
Use a base layer of aquatic soil or clay pellets, covered by a layer of sand or fine gravel to prevent soil displacement in water.
What is the impact of biochar or activated charcoal in terrarium substrates?
Biochar improves water retention, provides habitat for beneficial microbes, and helps store nutrients that are slowly released to plants. It is an excellent filter.
How to create a gradient in substrate layering for sloped or vertical terrarium designs?
Use materials like terrarium clay or wire mesh to support structured slopes, and layer substrates from coarse, drainage-promoting materials at the bottom to finer, nutrient-rich materials at the top.
What substrates are suitable for a terrarium with both aquatic and terrestrial zones?
Combine aquatic substrates like aquatic soil in the water zone with moisture-retaining terrestrial substrates like coco coir and sphagnum moss in the land areas.
How can expanded clay pellets be used in terrariums?
Expanded clay pellets or LECA are excellent for drainage layers due to their lightweight and high porosity, which helps manage moisture levels effectively. We use them for all of our terrariums.
What are the effects of glass transparency on substrate selection?
Glass transparency affects light penetration; clear glass allows more light and may require substrates that protect roots from light exposure, while tinted glass reduces light intensity and heat.
Can recycled glass be used as a substrate in terrariums, and what are its benefits and drawbacks?
Recycled glass can be used as a decorative element or drainage layer. It's aesthetically pleasing and sustainable but offers little nutrient or moisture support.
How do I make my terrarium layers Bioactive?
Simply include microfauna or mesofauna like Springtails, Isopods, earthworms or millipedes. Make sure to include sterilised leaf litter in your soil mix.
Should there be any nutrition in my terrarium soil mix?
We say yes, for healthy and natural growth of your plants. Some argue that removing all nutrition will prevent overgrowth. But, we think it’s much better to manage the quantity of nutrients rather than remove them entirely. See our recipes above.
Is a mesh layer essential?
For terrariums no – it’s not essential and we don’t recommend them. For vivariums yes, it can be useful to have a mesh layer separating your soil layer from the drainage layer.
Mesh layer + for vivarium?
Can I use aquarium soil as a substrate mix for terrestrial/land plants?
Yes! It is a sterile, nutritious, well-draining and well-aerating substrate mix.
is perlite safe for reptiles
No – it is not advised to use perlite in a vivarium set-up.
What soil does moss enjoy?
Many live mosses enjoy a clay-based acidic soil. This means our terrarium putty mix is perfect for moss-only terrariums. Though, our terrarium substrate mix works just as well, too.
They can be used in combination for more complex terrariums.
For example, putty can be used for a rear moss wall, while the terrarium substrate mix is used for the base.
Do you sell tropical terrarium kits and supplies?
Yes! You can find everything you need in our shop, online. Some items may only be available for UK delivery, so we included where to buy USA alternatives throughout this article.
And, that's a wrap! If you have any questions not answered in this article, leave a comment below and we'll add it to the list.
Don't forget to subscribe for updates on the release of our new articles!
- Joe
Leave a comment