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 the 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!

terrarium substrate

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The Key Components of an Effective Terrarium Soil Mix

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.

fluffy tropical substrate in hand
Light, fluffy, and well-aerated is the name of the game!

TL:DR – The Best Terrarium Substrate Mix

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.

👉 You can find our premium terrarium substrate on our shop!

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

Our Recommended Substrate Bases

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.

coco coir in terrarium
I like coco coir when it’s really finely ground like this batch.

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.

dried sphagnum moss fibers
This is a batch of long fiber, dried sphagnum moss.

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.

aqua soil pellets
These aquarium soil pellets are as versatile as they are hard to photograph…

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.

Useful Terrarium Soil/Substrate Supplements

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.

orchid bark chunks
A fine-grade orchid bark that I purchased.

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.

fine pumice chunks
Fine pumice just looks like lots of tiny stones.

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.

crushed lava rock chunks
I think I got “crushed red lava rock” to be exact.

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.

earthworm castings pile
Earthworm castings are pretty much indistinguishable from dirt.

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.

horticultural charcoal chunks
Here’s what you can expect from horticultural charcoal in terms of particle size.

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.

black terrarium sand
Sand like this can work as a standalone drainage layer too!

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.

tree fern fiber
Tree fern fiber kind of looks like a twiggy version of coir.

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.

perlite chunks in pile
Perlite really just reminds me of rice puffs.

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.

vermiculite chunks
Who knew vermiculite was so photogenic?!

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.

Not Recommended (Or at Least Not Ideal) Soil Materials

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.

Terrarium Substrate FAQ

Would you recommend buying a terrarium soil kit?

If you’re only ever planning on building a single terrarium, then sure. Getting the exact right amount will cut down on waste and make the build simpler. However, they are expensive for what you get, and you can’t always identify the source of each material or judge its quality.

What’s the best terrarium soil recipe?

There is no single best terrarium soil recipe, it will depend on your plants and other terrarium conditions.

What is bioactive terrarium substrate?

Bioactive terrarium substrate is designed to promote the growth of beneficial bacteria and fungi that help to support natural decomposition cycles and other biological processes.

Now, Over to You

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.

24 thoughts on “Terrarium Soil & Substrate – A Hands-on Guide (+ Best Mixes)”

  1. Hi ! We are are making our substrate with 1/3 bark, 1/3 potting soil, 1/3 sand and also add some activated charcoal.

    However we can not get a hold of spaghnum moss and we also feel like the sand is a little bit too much.

    Any advice :)?

    1. Hi Cedric, the sand and the bark should help a lot with aerating the potting mix, but you might find your substrate to be a little heavy with that ratio. If you can’t get a hold of sphagnum moss, coconut coir would be a good substitute to keep the mix a little lighter and fluffier.

  2. Hey! I’m working on my first terrarium build after finally deciding what to do with an antique Edwardian case I have, and I discovered some greenhouse frogs that made their way from my grandmother’s backyard, to my closed patio via an epidendrum orchid with moist soil. Theyre so tiny, and I think they’d like the finished product and getting as many bugs as they can handle. So, I’ve waterproofed the wooden case and decided to use Hydroballs and larger pebbles, charcoal (of course), and aquarium soil. I chose aquarium soil because of the clean compact pellets. Now that I just discovered ABG mix, I wonder if I should purchase a bag, or maybe add coir for some softness?

    1. Hey Brittany, your first terrarium sounds like an amazing project! I’ve been experimenting with aquarium soil for the same reason, I really liked the idea of a uniform soil solution but personally I found it quite awkward to plant in on its own. I’m looking to make it into a custom mix for my next build, and coir is definitely on my list to add to it. I’m afraid I can’t speak too much on creating a good habitat for frogs as I’ve no experience of keeping animals, but I do know that ABG mix is pretty much the go-to substrate for vivariums, so I would imagine it’s a much better fit for animals than aquarium soil.

  3. 1/4 coir, 1/8 compost, 1/8 topsoil. 1/10 or less of: charcoal, sand, spagnum moss, vermiculite, worm castings, hay. Suspend that mix on gravel, separated by screen. Cypress mulch and shredded leaves on top of the mix. What do you think? Any suggestions?

    1. Overall this sounds like a great mix for a vivarium, but if it’s just for plants there’s a few things I’d probably remove. The compost and mulch are both going to rapidly decompose, and if you’re already using worm casting you won’t need that level of fertiliser (or any at all really). Everything else sounds just fine, you’ll have plenty of water retention and drainage with a mix like that. Not sure on the hay now that I think about it. Hope that helps!

  4. I’m thinking of integrating live plants into my corn snakes tank. The plants being used aren’t super water-loving. This is the mix that I was told to make: 50% top soil, 25% sand and 25% coir, sphagnum moss, and vermiculite. Would you add/change anything to this mix for the most effective plant growth?

    1. Hey Kelly, I can’t comment on how suitable it is for animals, but it’s a reasonably balanced mix that should be fine for more drought resistant plants. Personally, I’d reduce the % of top soil as it can compact over time.

  5. Hey! I’m starting a 70 liter paludarium with a mixture of ferns (maiden hair etc) and emersed aquatic plants (anubias, java ferm, mosses).
    It will have about 2inches of water at the bottom under a drainage layer and a filter and fogger.

    Was thinking 1/3 to half of aquarium soil (oliver knott), 1/3 spagnum moss and the rest orchid bark.
    Does that sound ok?
    Thanks!

    1. Hey Sarah! Aquarium soil is a good all rounder – both terrestrial and aquatic plants can grow in it – so it’s hard to go too wrong with a mix using that as a base. Assuming the sphagnum and orchid bark are only being mixed in with the dry aquarium soil above the water line, they should hold up well.

  6. I am going to make my first terrarium. I have read so much it has only serviced to confuse me. What do I need to mix in with the store bought potting soil. I am going to purchase 10 terrarium plants from esty. Ferns, a dwarf palm, polka dot plant, etc. Please spells things out for me. I guess my main concerns are adding the proper mixture for nutrients, drainage and whatever else is needed. I feel totally confused from all I have read. Can you help me? 🙂

    1. Hey Des, I’m sorry to hear you’re struggling with your terrarium plans. If you’re set on using potting soil, you’ll likely want to add something like coco coir and sphagnum moss to “fluff up” the mixture, plus something like orchid bark for drainage and root aeration. Feel free to join the Facebook group if you have more questions! 😀

      1. You have a FB page? 🤩 I’ll join 💯
        Thank you for all your advice. It’s great 👌
        I’m a beginner in infant stage when it comes to terraniums but I am determined and have read so much on the topic, I dream about it 😂😂
        I found your advice in this forum the best and easiest to understand so far 👌
        Birgit from Melbourne, Australia

    2. Hi Dan! Thank you very much for this interesting article.
      I made some terrariums using potting soil, sand, pine bark and sphagnum moss. The texture is fine but I got the substrate flies in all of my closed terrariums, and it’s becoming quite difficult to get rid of them.
      I’ve been reading that potting soil is not ideal for closed terrariums. Do you think that this could be the reason why I get this black flies?
      Thank you!

      1. Hi Gustavo, yeah I’d say it’s most likely the potting soil – particularly if it has been open for a while. That being said, if the pine bark is damp and open it could be that too.

  7. Hello! I just created my first closed terrarium, and would like to add springtails to it soon for mold control on some driftwood. I used aquasoil leftover from a planted aquarium. Will springtails do all right in that kind of substrate?

    Thanks for all the helpful articles! This site has been an awesome resource so far.

    1. Hi Adrienne, I’m so glad you’re finding the site useful. 🙂 Springtails and aquasoil have been fine in my experience. The way the round pellets lie seem to leave plenty of space for them to maneuver.

  8. Hi Dan. I’m a very new (but very keen) terrarium creator and your site looks fantastic with lots of clear, balanced and useful advice.
    I want to create an (Arizona-ish) red dessert setting for an open cacti, succulent and mini scorpion terrarium and would love to cut up red house bricks as miniature rock formations (and the smaller bits to mix with my substrate). Are old, red house bricks safe to use for these plants in this situation?
    Thanks
    Nathan

    1. Thanks so much for the kind words Nathan! As far as I know, house bricks are just fired clay and should be absolutely fine with plants.

  9. Hi!
    I am SO glad I found this site! so much helpful info.
    I am a complete NEWBIE, never ever done a terrarium before and while working on a centerpiece for a fundraiser I fell in love with succulents, moss and something I would never have thought was so cool. Lichen. I bought British Soldier and Pixie Cup Lichen and have NO clue how to set up a terrarium to keep them alive. Is this something you can help with?
    Robin

  10. Wondering when you might choose to use coco coir vs sphagnum, or both? They seem to accomplish a very similar purpose in the mix

    1. They’re both super water retentive, but coir has the consistency closer to a typical planting medium so it’s better as a base for a mix.

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