ABG Mix – The Classic Terrarium Substrate Recipe

The ABG mix, first developed (and named for) the Atlanta Botanical Gardens has been the gold standard substrate in the terrarium and vivarium industry for many years.

If in doubt, this is a tried-and-tested option for tropical terrariums of all kinds. 

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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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 terrarium ecosystem.

The ABG mix is so effective because it balances each of those elements so well.

• Excellent drainage – so your plants are not drowning in soggy substrate.

• Great water retention – so your water-loving plants are well supplied, and it also helps to boost humidity to create that tropical environment.

• Retains nutrients – the peat moss doesn’t add any nutrients, but it’s incredibly effective at holding on to 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 – it can easily last years before losing functionality.

Surprisingly, it’s actually quite difficult to find the original 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!

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

These days you’ll often see coco fibre (coir) as part of the mix too, but we’ll cover substitutes at the end of the article.

If you want to grab a bag of accurate ABG Mix, here’s one on Etsy (via Glass Box Tropicals).

ABG mix is a soilless one.

Instead, it uses a variety of natural materials to mimic the native tropical soil layer of the rainforest environment.

Despite using traditionally fibrous and chunky base ingredients, the ABG mix is designed to be quite light and fluffy. This is partly thanks to the addition of several materials for that very purpose, but also due to each of the materials being used at a loose, fine granularity. 

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

Milled Sphagnum Moss

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

It’s fantastic at retaining moisture, 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-fibre 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!

• See dried sphagnum moss on Etsy.

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.

• See tree fern fiber here on Etsy.

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.

• See orchid bark on Etsy.

Peat Moss

The peat moss substrate is often confused with sphagnum moss because in many ways they come from the same source (and kind of share the same name).

Both come from peat bogs, where sphagnum moss loves to grow. The peat moss substrate we’re talking about is the decomposed organic material and sphagnum moss is the preserved fibrous filaments of the moss itself.

Make sense?

Peat moss is a bit of a wildcard material in the terrarium industry. Some people swear by its consistency and properties, hailing it as a fantastic terrarium substrate. Whereas others argue that the degradation rate of peat moss and unsustainable sourcing (peat bogs can take decades to renew) make it unsuitable for use.

Either way, in the ABG mix peat moss is included for its excellent water retention and uniquely powerful ability to retain nutrients.

Though I prefer to use coco coir (as explained later in the “Substitutes” section) as peat moss is so controversial and hard to source.

Charcoal

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

The recipe doesn’t indicate any one particular kind, but horticultural charcoal and activated charcoal are your best bets.

Activated charcoal is significantly more expensive but is more effective. It also comes in a relatively small particle size so it’s easier to mix into a susbtrate.

• See activated charcoal on Etsy.

It’s important to note that the interaction between these different components is important too. When it comes to the ABG mix and many other substrate mixes, the sum is indeed greater than its parts.

When you consider how the tree fern fiber framework might be supported by the chunkier bark pieces, and filled with fibrous filaments – we can begin to see why this mix is so effective at aeration and drainage.

If you’re struggling to get your hands on any one of these components (some are increasingly difficult to come by) then there are some more readily available options to try.

Plus, substituting the organic components (mainly peat moss) for inorganic options can make your substrate mix more resilient and last longer.

Just note, that although these substitutes mimic their replacements function, they are often structurally and chemically different. They’re not a 1-1 replacement, and they do fundamentally change the mix on a whole.

Coconut coir for peat moss

With excellent water retention properties, coconut coir can be a 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 which 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.

As far as substitutes go, this is the material most like its original and I much prefer it.

• See coco coir on Etsy.

Perlite for tree fern fiber

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

Though perlite is completely different in appearance and structure to tree fern fiber, it is also very effective at aerating substrate and improving drainage. 

So, even though it’s going to significantly change the consistency of the mix, it’s the most capable substitute at performing the function of tree fern fiber.

• See perlite on Etsy.

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 came up with your own recipe.