ABG Mix – The Classic Terrarium Substrate (+ Recipe)

ABG mix has been the gold standard in the terrarium and vivarium industry for many years.

First developed by – and named after – the Atlanta Botanical Gardens, it’s a tried-and-tested option that brings a lot of benefits to the table. 

I’ve personally used variations of this classic mix in a wide variety of terrariums with (mostly) great success. So, in this article, we’re going to break down the components that make this mix so special and effective.

Plus, we’ll share the ABG mix recipe so you can make your own!

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For starters, substrate mixes are almost always superior to single substrate choices.

Each element of the mix plays a different role in supporting plants and facilitating a healthy terrarium ecosystem. The ABG mix is particularly effective because it balances each of those elements so well.

• Excellent drainage – In a closed system, drainage is essential to keep your plant’s roots healthy and aerated (and not drowning in a soggy substrate).
• Great water retention – Ensuring your water-loving plants are well supplied, and it also helps to boost humidity to create that tropical environment.
• Retains nutrients – Though the peat moss doesn’t add much in the way of nutrients, it’s incredibly effective at holding onto them.
• Resists compaction – With so much spongy, fibrous material in the mix, it’s able to stay well aerated and resist compaction over time.
• Long lasting – This mix can easily last years before losing functionality.

Surprisingly, it’s actually quite difficult to find the source citation for the ABG mix recipe.

And if you ask any expert what it was, you’re likely to receive a slightly different answer! Though based on my research, it seems the original recipe was as follows:

1. Sphagnum Moss – 1 part
2. Tree Fern Fiber – 2 parts
3. Orchid Bark – 2 parts
4. Peat Moss – 1 part
5. Charcoal – 1 part

Putting this recipe into practice, I believe these ratios are set in volume rather than weight, as weight can vary a lot depending on the material.

And though this is the original recipe, you’ll now see many variations available on the market. So don’t be surprised if the materials list of a purchased pre-made mix doesn’t match this exactly.

So, in the rest of this article, we’re going to deep dive into these materials and show you how to substitute them where necessary.

If you want to grab a bag of classic ABG Mix, here’s one on Etsy

👉 Or, if you’d like to see our take on ABG mix – shop our Terrarium Substrate Mix.

ABG mix is actually classed as a soilless substrate.

Despite using traditionally fibrous and chunky base ingredients, the mix is designed to be quite light and fluffy (and it pulls it off).

This is partly thanks to the addition of several materials chosen for that very purpose but also due to each of the materials being used at a loose, fine granularity.

It’s designed to mimic the native tropical soil layer of the rainforest environment, so it’s an ideal substrate for bioactive vivariums and terrariums.

So, if you’re making this mix yourself, it’s important to get the right kinds of ingredients to get the ideal consistency.

1. Milled Sphagnum Moss

Of course sphagnum moss features in this list; it’s a true terrarium staple.

It’s fantastic at retaining moisture and boosting humidity, and it helps to create an acid environment that slows the rate of decay.

You’ll typically see “milled” sphagnum moss listed in the recipe, and it’s essentially just sphagnum that’s been ground down to a fine grain.

If you can’t find it at this consistency, I’ve seen forum users recommend just throwing the long-fiber sphagnum moss in a blender or chopping it up with a knife.

In my build for the Essential Guide to Tropical Terrariums – I just ripped it up a bit with my fingers!

👉 Shop sphagnum moss on Etsy.

2. Tree Fern Fiber

Sourced from a variety of tree fern species (often Dicksonia), this versatile material looks like heaps of tiny twigs and really adds an element of natural aesthetic to a mix.

Tree fern fiber is primarily there for aerating the substrate and providing drainage.

The twig-like shapes form irregular frameworks in the mix, supporting the overall structure, resisting compaction, and creating air pockets.

👉 Shop tree fern fiber on Etsy.

3. Orchid Bark

Orchid bark (named for what it’s used for, not where it comes from) serves a similar purpose to the tree fern fiber in providing drainage and aeration.

The material comes in a variety of degrees of “chunkiness” depending on how it’s processed and what trees it’s sourced from (fir bark being the most commonly used).

Ideally, you’ll probably want to find orchid bark at the smallest possible particle size.

👉 Shop orchid bark.

4. Peat Moss

Peat moss is a more controversial substrate element.

It’s often confused with sphagnum moss because, in many ways, they come from the same peat bog source (and kind of share the same name), but they’re very different things.

Peat moss is typically included for its excellent water retention and uniquely powerful ability to retain nutrients. Plus, it has a nice fine texture that’s good for planting in.

But sadly, it’s a non-renewable product, so it’s getting less use over time (we don’t personally use it for this reason).

I prefer to use coco coir, as explained later in the “Substitutes” section.

5. Charcoal

Charcoal is often used in terrariums for its ability to filter any water that passes through it, thus “sweetening” the substrate.

Due to its porosity, it can also help with water retention and aeration too.

Though the recipe doesn’t indicate any one particular kind, horticultural charcoal, and activated charcoal are your best bets from a filtration point of view.

Being the most porous of all (by a large margin), activated charcoal is arguably the most functional, but it’s also the most expensive. Horticultural charcoal sits somewhere in the middle as a happy medium.

Just note not all types of charcoal are suitable for terrariums – so it’s important to choose the right kind. Check out my guide to terrarium charcoal for more help.

👉 Shop activated charcoal.

With any good substrate mix, the sum is greater than its parts

Each element plays an important role, but the interaction between them is critical to success too.

In this case, consider how the tree fern fiber framework might support the chunkier bark pieces and finer fibrous elements. We can begin to see why this mix is so effective at aeration and drainage.

That’s why adapting a mix isn’t always quite as simple as it may seem.

However, with a variety of the original recipe ingredients being either expensive, hard to find, or unsustainable, it’s worth exploring ways to do it.

I always recommend ABG mix as a starting point, but I’ve never actually used the original recipe.

For me, peat moss is a definitive no, and tree fern fiber is too difficult to source sustainably (or at least without spending a fortune). Plus, as good as the ABG mix is, it can always be fine-tuned to better serve your desired setup.

So, shall we jump to my recommended material substitutes?

*Wait, hold up. I just want to make one thing clear before I’m flamed into oblivion. These are not 1-1 replacements, and they do fundamentally change the mix as a whole.

 I’m not saying these substations are perfect, but they’re the best fits that I can think of – so let’s see them.

Peat Moss -> Coconut Coir

With excellent water retention properties, coconut coir can be a good substitute for peat moss.

Peat moss decays over time, which on one hand, is a good thing as it releases nitrogen into the substrate (which can help support plant growth). But, on the other hand, you have an organic component that is eventually going to fully break down and spoil (normally in a few years).

Coconut coir overcomes this as it’s a completely inert, very stable material. So it won’t degrade for a very long time, but nor will it support plant growth in any way.

Adding in some earthworm castings can substitute some of the nutrients, too.

👉 Shop coco coir.

Tree Fern Fiber -> Pumice or Lava Rock

Tree fern fiber is often the most difficult component to source and, frustratingly, the most difficult to accurately replace.

Though pumice and lava rock are both completely different in appearance and structure from tree fern fiber, they’re also very effective at adding aeration substrate and improving drainage.

So, even though it’s going to significantly change the consistency of the mix (rocks and twigs are very different things), they’re arguably the most capable substitutes for performing the function of tree fern fiber.

Do you use ABG mix in your terrariums or vivariums? I’d love to hear from you!

Particularly if you’ve substituted any ingredients or come up with your own recipe.