Terrarium Substrate & Soil – Which is Best For You?

Terrarium soil and substrates are clearly the least exciting part of a terrarium build (it takes a committed botanist to get excited about dirt) but it’s still a critical part of your terrarium. 

Get it wrong and you’re at risk of stunted plant growth, rot, bug infestations and more. 

Sure, you could just grab a handful of soil from your backyard and hope for the best, but it’s a good idea to at least check what you’re putting in.

In this article, we’re going to cover all the basic questions about terrarium substrates, so you know exactly what you should be putting in your terrarium and where to find it.

(You can also check out my Essential Guide to Tropical Terrariums for a full breakdown on my recommended substrate mix).

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Terrarium Soil/Substrate Bases

Coir (Pronounced Kwoy·uh… Apparently)

Coir is a fibrous material made from coconut husks.

As you might imagine, it’s dry as hell when you get it in brick form, but once it’s hydrated it can retain a ridiculous amount of moisture.

Its advantages for terrariums are due to it being a very stable and reliable material. You’re able to better control moisture and drainage versus using soil bases, and because it’s not found in nature (in this form) it’s not susceptible to pests.

However, it contains no nutrients whatsoever. So unless you’re mixing it with another substrate or adding fertiliser can help to support your plants.

It’s definitely worth a consideration as part of a substrate blend. You can grab a block here on Etsy for pretty cheap.

I like coir when it’s really finely ground like this batch I received.

Pros

  • High water retention
  • Neutral pH and resistant to decay
  • Readily available in brick form.
  • Natural, sustainable product.
  • Pest resistant

Cons

  • Contains no nutrients
  • Prone to compact over time if used on its own.

Sphagnum Moss

Sphagnum moss has become a true staple in the terrarium and vivarium industry (in both it’s live and preserved form).

This wonder material is fantastic for terrariums thanks to it’s excellent water retention and its fluffy texture that allows for lots of aeration.

Though perhaps just as important is the acidic 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 sphagnum moss from a variety of shops here on Etsy.

Sphagnum Moss Pink
Just look at this vibrant pink sphagnum moss! (live)

Pros

  • High water retention
  • Acidic pH and actually slows decay
  • Readily available
  • Natural, sustainable product.
  • Pest resistant

Cons

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

Potting Soil / Potting Mix

Regular packaged potting soil is a universally available option.

It’s affordable and it will work for many terrarium plants, 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.

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.

Grab a bag on Amazon right here and try it yourself!

Aquarium soil I’m trying

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 plant’s roots down into it like you would a soft substrate.

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

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 terrariums. 

If you’re building a tropical terrarium, perlite can be a useful addition to your soil mix.

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. Grab a bag here.

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.

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.
  • 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.

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.

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.

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. 

Earthworm castings have a very fine texture like loose soil.

A nice way of saying “worm poop”, earthworm 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 the range of earthworm castings on Etsy.

Classic Terrarium Substrate Mixes

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 the vivarium industry.

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

Make Your Own DIY Terrarium Soil/Substrate Mix

Even if you use the same plants and materials as someone else, every terrarium is unique. 

Where you live, where you place your terrarium, how you care for it – they all require a slightly different soil solution.

A custom soil mix is sometimes the best approach as no one size fits all, but it can be a little daunting to figure out yourself.

My 4 Step Soil Solution

I see custom soil mixes as a gradient. You start off with a base then add differing amounts of soil supplements depending on your circumstances.

  1. Base – Select a base material according to the type of plants you want to grow (e.g. coir or soil). This should make up to half of the overall mix.
  2. Compost – If necessary for your plants, add earthworm castings or similar. About 10% of your overall mixture should be sufficient.
  3. Moisture retaining materials – Supplement with sphagnum moss, vermiculite or perlite depending on how water-loving your choice of plants are.
  4. Aerating elements – Add where necessary depending on how much drainage your plants need (e.g. sand or orchid bark).

Generally, an effective substrate should be made up of no more than 50% of the base material. Any more can result in a heavy, soggy sponge of a substrate. So you can expect to supplement heavily with aerating and moisture retaining materials to achieve the right mix.

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.

15 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 he pine bark is damp and open it could be that too.

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