Terrarium Soil & Substrate – A Hands-on Guide (+ Best Mixes)

Figuring out the right terrarium substrate may be dirty work, but it’s a critical step in any project.

Think of it as the foundation of your entire ecosystem. It gives your terrarium shape, function, hydration, and nutrients – so it’s important to get the right mix for the job.

Especially considering different terrariums have different needs, just like us.

Thankfully, working with a terrarium soil mix (instead of a single material) gives us the flexibility to adapt to any project. Anything you need, we have a super substitution to create a winning formula.

And for those who just want a surefire terrarium soil mix that’s going to do the job – we have that too.

So buckle up for a complete guide on the optimum blends for your next project (along with deep dives on individual elements, too).

Let’s dig in!

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Like a good cocktail recipe, every ingredient is designed to balance and complement one another.

A certain sweetness to the sour, shall we say? Margaritas, I’m looking at you…

The same is true for a terrarium substrate mix. You’re aiming to achieve the ideal balance of water retention, drainage, aeration, and support.

Naturally, it can be a bit daunting at first, but that’s why we have an easy-to-follow recipe!

Starting with an appropriate base, you can then tailor the choice (and amount) of soil supplements depending on the needs of your chosen plants and environment.

• Base – The base makes up the core of your mix and provides both support and water retention. It typically makes up about half of your overall substrate.
• Structure – These are the more granular materials that provide some much-needed drainage and root aeration for your plants. Some materials can provide boost water retention/availability too.
• Compost – If you’re using completely inorganic components (or you like to give your plants a head-start), you will need to supplement with some organic material.

Fear not; whether you’re a seasoned soil mixologist or you’re new to the indoor gardening game, all will become clear.

I get it; not everyone has the time to formulate the perfect mix for every setup.

Thankfully, some tried-and-tested tropical mixes (such as ABG mix variations) will hit the mark 99.9% of the time. And that’s why we’ve developed our own substrate mix for terrariums and vivariums.

It’s a precise mix of orchid bark, earthworm castings, coco coir, horticultural charcoal, and (optionally) pumice.

The blend of materials provides excellent water retention and drainage, making it a great option for tropical plants of all varieties.

Now, the rest of this article is for all you DIY-ers!

We’ll outline all of our recommended materials for each part of the recipe and how to decide which one is right for you!

1. Coir

Coco coir is a fibrous material made from coconut husks, and it’s my favorite substrate base to work with.

It comes in a variety of forms, from dry bricks (that need rehydrating) to bags of coarse chips and finely ground powders – the latter of which is best in my experience.

The larger chips/fibers arguably provide better drainage, but the powder is a dream base to plant in.

It’s super light and fluffy, which means you’re going to get lots of root aeration and tonnes of moisture retention. Plus, it’s not going to compact over time.

What’s not to love?

Well, coir is also popular as a base for its stability and reliability.

As a refined material, it’s not going to break down in your terrarium (at least not for a very long time), and it’s resistant to pests.

👉 Convinced? Check out the coco coir on our shop.

The one caveat is that it contains no nutrients whatsoever. So, to properly support your plants, you’ll have to add a fertilizing element to your substrate, but more on that later.

Pros

• High water retention.
• Neutral pH and resistant to decay.
• Natural, (more) sustainable product.
• Pest resistant.

Cons

• Contains no nutrients whatsoever.

2. Sphagnum Moss

Sphagnum moss has become a true staple in the terrarium and vivarium industry.

It’s popular in both its live and preserved forms, but preserved is more common for substrates.

Just like coir, this versatile material is fantastic for terrariums thanks to its unparalleled water retention and its fluffy texture.

Though perhaps just as important is the antimicrobial properties of sphagnum moss, which help to reduce bacterial growth. And therefore slow the rate of decay.

A valuable characteristic in a terrarium environment!

Sphagnum is often used on its own as a growth medium, sometimes as a substrate barrier, and often as a supplement to mixes. It’s arguably a base material and a potential supplement, depending on how you use it.

👉 You can purchase bags of preserved sphagnum moss from a variety of shops here on Etsy.

The main caveat with this one is that it’s not an easily renewable product, so you’ll have to do your due diligence to get it sustainably.

Pros

• High water retention.
• Slows decay and improves soil health.
• Pest resistant.

Cons

• Contains no nutrients, so not for use in isolation.
• Will eventually break down (but we’re talking a seriously long time).
• Many sources are unsustainable.

3. Aquarium Soil

Aquarium soil is regular soil that has been baked to produce dry pellets.

It’s an interesting option because it has all the minerals and positive growth aspects of regular potting soil but with much better drainage.

That’s because the pellets are round, so they don’t pack together in a uniform shape. They’re also pretty tough, so they’ll resist compaction for years.

Aquarium soil has become a lot more popular recently, and it’s probably the only substrate that can be used on its own. Though on its own, I find it hard to plant in, so I still think it’s best as a base rather than an all-in-one solution.

👉 Grab a bag on Amazon right here and try it yourself.

Pros

• It’s stable and won’t compact for years.
• Excellent drainage and water retention.
• A great option for a paludarium.

Cons

• The aesthetic of lots of little black balls may not be for everyone.
• The soil pellets are so tough that I find it a little tricky to plant in sometimes. You can’t simply press a plant’s roots down into it like you would a soft substrate.

1. Orchid Bark

Orchid bark is a more natural way to add granularity and aeration to a soil mix.

It’s a chunky mix of bark shavings (named because it’s often used for orchids; it doesn’t come from them) that helps to provide structure and spaces in a soil medium.

Finding a mix that’s small enough for terrariums is the tricky part; it’s often super chunky.

👉 Check out orchid bark on our shop.

Pros

• All natural, sustainable material (that actually looks natural!).
• Great for root/soil aeration.
• Brings some degree of water retention.
• Bioactive material.

Cons

• Arguably more susceptible to rot, seeing as it’s a natural product.

2. Pumice

Pumice is a type of volcanic glass that’s more of a smooth gravel.

Often used in the bonsai industry, pumice has a lightweight honeycomb structure and an open porous exterior, making it an excellent soil aerator and moisture retainer.

A wonderful little rock with a lot of versatility.

There are a tonne of different kinds of pumice in all manner of sizes, colors, and compositions. Some of it can actually be quite soft/brittle, which I wouldn’t recommend if you’re using it to provide structure, too.

👉 I’d recommend a finer grade like this horticultural pumice.

Pros

• Great for aeration & water retention.
• Good drainage.
• Natural looking.
• Lasts indefinitely.

Cons

• None to speak of.

3. Lava Rock (Scoria)

As you might imagine from the name, lava rock is another volcanic horticultural material.

Sharp, dark, and non-uniform, it can provide some real structure to a mix. Though it’s heavier than pumice, it still provides plenty of aeration and water retention.

The large surface area can also help promote beneficial bacteria in bioactive setups. I’ve used lava rock as both a drainage layer and a substrate element, and I’m a big fan.

👉 I prefer aquarium-grade crushed lava rock, which is nice and small in grain size.

Pros

• Great for aeration & drainage.
• Can be used to wick water upwards.

Cons

• Difficult to find small particle sizes. 

4. Earthworm Castings

If you’re running with pure coir as your soil base, you’re going to need to add some nutrients to your growth medium.

I’d be wary of adding any homemade compost that may contain any rotting material, and I’d definitely opt for something packaged where possible.

Earthworm castings are a great, readily available solution.

A nice way of saying “worm poop,” worm castings are compost produced through the feeding actions of earthworms.

It’s an all-natural fertilizer, which is also well-draining and has a high water-retention capacity.

👉 Grab a bag of earthworm castings here.

Pros

• Eco-friendly.
• Slow-release nutrients vs liquid fertilizer.
• Has moisture-retaining properties.

Cons

• None!

5. Charcoal

Charcoal has been a horticultural staple for a long time, but its use in terrariums is a lot more varied.

Thanks to its highly absorptive nature, it’s able to bind to terrarium contaminants – making it an often touted “cleaning” material. Though the effectiveness of this action isn’t easily quantified, it may prove to be a lifesaver.

Plus, charcoal still brings other positive qualities to a substrate mix.

It’s able to retain moisture thanks to its porosity and is often described as being able to store and provide nutrients to plant roots.

It comes in a variety of forms, but horticultural charcoal and activated charcoal are likely your best bets.

Smaller chunks are the easiest to distribute as part of a substrate mix, or you can opt for larger pieces if you’re using them as a dedicated layer.

👉 See the activated charcoal on our shop.

Pros

• Odor and toxin binding capabilities.
• Moisture-retentive.
• Excellent soil aerator.

Cons

• Activated charcoal can be expensive.
• Can spike soil pH in large quantities.

6. Sand

Sand can be an easy addition to your substrate to increase its aeration and drainage.

Coarser horticultural sand will be best, but any sand will do (barring sand from the beach).

Obviously, if you’re going for a desert terrarium, you’ll have a much higher proportion of sand. The same goes for any cactus or succulent mix.

Personally, I prefer to use black sand where possible. That way, it’s less visible in the substrate, and the darker substrate contrasts better with green plants.

👉 Shop black sand on Etsy.

Pros

• Great for drainage and structure. 
• Maintains a nice, fine substrate consistency.

Cons

• Doesn’t offer any other value beyond drainage.

7. Tree Fern Fiber 

Tree fern fiber is an interesting material in that it looks like lots of tiny fine twigs. 

Kind of like how you might stack branches on a fire; it brings a unique structural dynamic to a mix.

Though, despite being a founding member of the ABG mix ensemble, tree fern fiber doesn’t see as much use as other materials on this list.

Mostly because it’s difficult to source (even more so in a sustainable way), but it’s tough to find a good substitute for, too.

👉 I’d recommend Fernwood New Zealand tree fern fiber for a sustainable source.

Pros

• Brings a unique structural quality to a mix.
• Natural product with a natural look.

Cons

• Can be expensive and difficult to source sustainably.

Perlite

Perlite is another type of white volcanic glass that kind of looks like styrofoam balls.

Its light and porous composition could, in theory, bring a variety of benefits to tropical terrariums.

The unique structure allows it to hold on to water on its outer surface without absorbing it internally – making it a solution to provide consistent water to plants without creating a soggy mix.

The granular structure of the material also helps to aerate a substrate mix.

All that said, when it comes to terrariums, I find there are better choices out there than perlite, e.g., lava rock or pumice.

👉 I do find myself using perlite in my potted mixes, though – shop it here on Etsy.

Pros

• Perlite will not rot, degrade or break – making it a reliable long-term soil addition.
• Because it’s so porous, perlite is great at aerating soil and providing better drainage.

Cons

• White styrofoam ball lookalikes don’t look particularly natural in a terrarium (I don’t like the look of them at all).
• Due to being so light, I have heard of them “floating” toward the top of a growth medium. I doubt you’ll wake up one day to find them all on top of your plants, but it’s something to bear in mind.

Vermiculite

Vermiculite is often lumped in with perlite, but it has a very different appearance, structure, and use.

For starters, it’s actually a mineral (aluminum-iron magnesium silicate) and looks like brown, flaky rocks. But it’s surprisingly soft and spongy.

Where vermiculite really shines is in water retention. This stuff can really hold on to a tonne of moisture and, interestingly enough, nutrients too.

It’s not something I personally tend to use in terrariums, but I can see myself potentially using it for super water-hungry plant species.

👉 Check out Etsy to find a range of vermiculite grades (particle sizes) that should be great for terrariums and other smaller pots.

Pros

• Unlike perlite, vermiculite actually retains and provides nutrients for growth.
• Provides one of the highest possible water retention of terrarium soil additives.

Cons

• Doesn’t provide much aeration/drainage.

1. Potting Soil / Potting Mix

Regular packaged potting soil is a universally available option.

Sure, it’s affordable, and it will work for some plants, but it’s just not ideal for terrarium longevity.

The real weakness in potting soil is its poor drainage and tendency to compact too much. We all know what happens to wet soil. It just turns to thick mud…

Not ideal growing conditions for any plant, and many tropical terrarium plants simply won’t tolerate it.

It’s worth noting that “potting mix” can mean a variety of things. It probably includes some of the other materials on this list (which isn’t necessarily a bad thing), but it’s important you know what you’re getting.

2. Native Soil

If you’re making a native terrarium (i.e., using local ingredients), then soil taken from the local area is one option.

Without knowing its composition, it’s a bit of a gamble.

Native terrariums bring in a lot of unknown factors, and the soil may carry things like rot, disease, or pests. But if the plants are thriving outside, in theory, they should thrive in a similar enclosed environment.

SerpaDesign made a great video on how to source materials for native terrariums if you’re interested in going this route.

What’s your preferred terrarium soil mix?

I’d love to hear some specific examples of what mixes you use for different plants. After all, the more we know, the better we can look after our plants.

Share them in the comments below.