Terrarium Substrate & Soil – Which is Best For You?

Terrarium substrates are the well-balanced diet that forms 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!

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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, 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!

Coir (Pronounced [Kwoy-uh]… Apparently)

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 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, and 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 fertilizing element to your substrate, (but more on that later in the article).

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 its 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 help 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.

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 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.

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 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 sterilized, 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.

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 its 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.

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.

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 its 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.

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.

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 fertilizer, which is also well-draining and has a high water-retention capacity.

See earthworm castings on Etsy.

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.

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 (check out my succulent terrarium guide for more info).

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.

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.

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.