Terrarium Substrate & Soil – Which is Best For You?

Terrarium substrates are the well-balanced diet that form the foundation of your system.

There to support form and function, and to provide nutrients and hydration – they’re an (unavoidably dirty, but) essential part to the whole terrarium process.

Ultimately, what you choose to plant in will determine how your plants are able to grow and nourish themselves.

And every plant has different needs…

Get it wrong and you’re at risk of stunted plant growth, rot, bug infestations and more. So, it’s always worth taking the time to consider the best substrate mix.

Oh, you thought it was a one and done deal? Sorry, a mix is always the better choice – so buckle up for a complete guide on how to prepare the optimum blend for your next project (along with deep dives on every individual element).

Let’s dig in!

Terrarium soil & substrates

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The Key Components of a Substrate 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, support and strength.

Which can be a bit daunting at first, but that’s why we have a recipe!

Starting with an appropriate base, you add differing amounts of soil supplements depending on the needs of your plants and environment.

  1. Base – The base makes up the core of your mix (about half overall) and provides both support and water retention.
  2. Structured elements – These materials provide some much needed drainage and root aeration for your plants.
  3. Moisture retaining materials – If necessary, supplement with additional water retentive materials depending on how water-loving your choice of plants are.
  4. 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 mixologist or you’re new to the game, all will become clear.

The rest of this article outlines all of our recommended materials for each part of the recipe, and how to decide which one is right for you!

Recommended Terrarium Soil/Substrate Bases

Coir (Pronounced [Kwoy-uh]… Apparently)

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

It comes in a variety of forms; from a single dry brick (that needs re-hydrating), 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 to plant in. It’s super light and fluffy, which means you’re going to get lots of root aeration, tonnes of moisture retention and it’s not going to compact over time. What’s not to love?

Well, coir is so popular as a base is 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), it’s not susceptible to pests, and you’re able to more easily control moisture and drainage versus using random soil bases.

Convinced? Check it out on Etsy.

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

Coco coir
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

Sphagnum Moss

Sphagnum moss has become a true staple in the terrarium and vivarium industry (in both it’s live and preserved form, but preserved is best for substrates).

Just like coir, this wonder material is fantastic for terrariums thanks to its excellent water retention and its fluffy texture. Though perhaps just as important is the antimicrobial properties of Sphagnum moss, which helps to reduce bacterial growth and therefore slow the rate of decay.

A valuable characteristic in a terrarium environment!

It’s often used on it’s own as a growth medium, sometimes as a substrate barrier, and often as a supplement to mixes. Sphagnum moss is so versatile 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.

Preserved sphagnum moss
This is a batch of long fiber, preserved sphagnum moss.

Pros

  • High water retention
  • Acidic pH and actually slows decay
  • Readily available
  • 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.

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 it’s 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.

Aquarium Soil
These aquarium soil pellets are a tad wet and incredibly hard to photograph…

Pros

  • It’s stable and won’t compact for years
  • Excellent drainage and water retention

Cons

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

Not Recommended (Or At Least Not Ideal) Terrarium Soils

Potting Soil / Potting Mix

Regular packaged potting soil is a universally available option.

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 a 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.

Pros

  • It’s affordable and easily available.
  • It comes full of nutrients for your plants.
  • It’s sterilised, so you can be sure you’re not adding any bacteria or creepy crawlies to your mix that could pose a risk to your terrarium.

Cons

  • Pure potting soil really doesn’t drain well so your terrarium runs a higher risk of rot. 
  • Not good for tropical plants which don’t tend to like soggy soil.

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 it’s 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 terrarium building if you’re interested in going this route.

Useful Terrarium Soil/Substrate Supplements

Now, we get to the list of ingredients that build upon your base, and balance the overall mix.

Many of these materials serve similar purposes, but they all have slightly different pros and cons. So, it’s worth understanding your options before you make a final selection.

Perlite

Perlite is a type of white volcanic glass, that kind of looks like styrofoam balls. It’s light, porous and has a variety of uses in tropical terrariums. 

Its unique structure allows it to hold on to water on it’s outer surface, without absorbing it internally – making it a great 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.

A little bit of perlite goes a long way, see it here on Etsy.

Perlite
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 (perfect for tropical plants).

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” towards 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 very similar to perlite in function, but has a different appearance and structure. It’s actually a mineral (aluminum-iron magnesium silicate) and looks like brown flaky rocks.

It’s even better at retaining water than perlite, and can be a great addition to substrates for particularly moisture-hungry tropical plants.

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

Vermiculite
Who knew vermiculite was so photogenic?!

Pros

  • Unlike perlite, vermiculite actually retains and provides nutrients for growth.
  • Looks more natural than perlite (in my humble opinion).
  • Provides the highest possible water retention of terrarium soil additives, making it the best solution for water loving plants.

Cons

  • Doesn’t provide as much aeration/drainage as perlite does.

Pumice

Pumice is another type of volcanic glass that’s more of a gravel than it’s foamy white counterpart.

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 lots of versatility, I’d choose this if you’re looking for a more natural looking perlite.

Etsy has a wide range of pumice grades/sizes, but I’d recommend a finer grade. See them here.

Fine pumice
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.

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.

Explore the range of orchid bark sizes and mixes here on Etsy.

Orchid bark
A fine grade orchid bark that I purchased.

Pros

  • All natural, sustainable material.
  • Actually looks natural!
  • Great for root/soil aeration.

Cons

  • Doesn’t retain water as well as perlite or vermiculite.
  • More susceptible to rot, seeing as it’s a natural product.

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. Be wary of adding any homemade compost that may contain any rotting material, 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 all natural fertiliser, which is also well-draining and has a high water-retention capacity.

See earthworm castings on Etsy.

Earthworm castings
Earthworm castings are pretty much indistinguishable from dirt.

Pros

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

Cons

  • None!

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, 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.

A fine powder is the easiest to distribute as part of a substrate mix, or opt for a chunky option if you’re using it as a dedicated layer.

See activated charcoal on Etsy.

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

Sand

Sand can be an easy addition to your growth medium 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. 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.

See black sand on Etsy.

Reliable Terrarium Substrate Mixes

I get it, getting a custom substrate mix spot-on can be tricky, and sometimes you might just want to run with a tried-and-tested mix.

This section outlines some of the more popular mixes, or you can also see our Essential Guide to Tropical Terrariums where we make it easy for you by breaking down our signature mix in ratio format.

ABG Mix

Named for it’s original development by the Atlanta Botanical Garden (not an abbreviation for its ingredients as you’d think) ABG mix is pretty much the gold standard substrate for vivariums.

It’s a precise mix of tree fern fiber, peat moss, cocofiber, charcoal, and orchid bark. Though the proportions seem to vary depending on where you see the recipe.

The blend of materials provides excellent water retention and drainage, making it a great option for tropical plants of all varieties. If the above DIY recipe doesn’t work for you, here’s the classic cocktail that’s hard to mess up.

If you’re after a substrate blend, but scared of getting it wrong, ABG mix could be a good starting point for you.

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.

17 thoughts on “Terrarium Substrate & Soil – Which is Best For You?”

  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.

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