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Substrates – the whys and wherefores

So what do we mean – exactly – when we use the word substrate? According to the dictionary, it’s another word for substratum, meaning what lies beneath.

The substrate, then, is what we put on the floor of our animal’s habitat under the decor. It’s what our animal walks on, where it makes its home, and what it interacts with every time it moves around the space it lives in. It can be loose, tiled, carpeted or bioactive according to species and/or inclination of the owner – but what is the difference, and why should we choose one over another?

The choice is utterly bewildering, and the horror stories bandied about online as to the consequences of choosing badly can be horrific, at best. So let’s go back to first principles.

Why do we need substrate?

Well, we need a floor! This floor covering can serve several purposes: it can affect humidity levels, provide environmental enrichment for the enclosure’s inhabitant, and can add to the aesthetics of the enclosure.

But isn’t it dangerous?

Let’s get this one out of the way right at the beginning! Yes, if an animal eats substrate (a behaviour called pica), it can cause it a problem. And it’s certainly true that if you remove the substrate completely, you remove the possibility of that happening. But in the wild animals run around on, hide in and feed on the dirty ground, and are ingesting foreign material all the time; the difference is in the environmental conditions. They are exposed to the appropriate levels of UV, temperature, and humidity for their species. Everything they are exposed to they have spent tens of thousands of years evolving with, and their systems exist in harmony with their surroundings.

So when an animal exhibits abnormal behaviour (in this instance, pica), we need to look at the entire habitat. Taking this holistic approach will prevent problems occurring in the first place, and will quickly correct any that do occur.

In short, don’t blame the substrate – it’s a symptom, not the disease.

There are so many! How do I choose?

We are often asked which substrate is best. Well, that’s a difficult question!

If we take the holistic approach mentioned above, it makes selection a little easier. Where does your pet live in the wild? Is it a forest species, does it live in dry grassland, rocky deserts, up a tree, down a burrow? Looking at where they evolved to thrive will tell you an enormous amount about what they need to be happy in captivity.

Once we’ve narrowed it down to dry or humid, we need to consider what type of substrate to use. Do we go with a small grain, like a fine sand, or a soil based one, or wood chips? It’s a balancing act between what would be found in the wild and what works for us.

It’s easier for some species than others, of course; bearded dragons, leopard geckos and corn snakes have been kept and bred in captivity for so long that they are extremely adaptable when it comes to the surface they walk on. This doesn’t mean that you shouldn’t choose carefully, simply that you have a wider range to choose from!

So what are my options?

Let’s start with dry conditions. These substrates work for our arid habitat pets – bearded dragons, leopard geckos, corn, rat and king snakes, and desert specialists such as uromastyx.

Beech chip

This comes in two grades, fine and coarse. It’s fairly absorbent, easy to spot pick, and holds heat well. Economical to use.

ProRep Beech Chips Coarse

Aspen and Hemp 

Very good for snakes that like a drier habitat, this is a finely ground substrate that holds its shape and allows them to burrow. Absorbent and with a low dust content.

ZooMed Aspen Snake Bedding 4.4L


Fine, dust extracted wood chip. Very like sawdust, but less likely to cause respiratory problems. Excellent for snakes.

ProRep Snake Life Lignocel Substrate

Desert Sand

The classic dry substrate for arid habitat lizards. Although not many of our pet lizards originate from dry sand deserts, this substrate works well for many of them. Allows digging behaviour.

ProRep Desert Sand

Calci Sands 

Somewhat controversial! Very fine sand that, when used correctly, is perfectly safe – not suitable to be used as a supplement, but absolutely fine when simply used for floor covering.

ZooMed ReptiSand Natural Red 9kg (20lb)SR-20

Ground walnut/Corn cob

Slow to break down, dust free, fine and free flowing. Available in several grades.

ProRep Ground Walnut Sand, 5 Litre

Soil/Sand mixes

Soil based substrates are becoming more popular. They are very natural, and can give a humidity gradient for species that like to dig down – very important for Mediterranean tortoises.

ProRep Beardie Life

What about forest species?

For forest species we are trying to replicate the damper, more humid conditions found on the forest floor. These substrates hold more water, and play their part in maintaining an overall higher humidity in the environment. Each of these can be combined to make a flooring that is more wet, or more dry, or easier to burrow in – the variety is endless!

Bark Chips

Also known as orchid bark, this is slow to break down and holds humidity quite well. Made from softwoods like fir and pine, it can also be used in conjunction with a finer substrate.

Lucky Reptile Eco Bark 10L

Cypress mulch

More popular in the USA than here in the UK, this holds humidity well and is slow to rot.

ZooMed Forest Floor Bedding 8.8L, CM-8

Coco Fibre

Made from coconut husk milled down to various grades – from flat chunks to a fine grain size – this holds water almost as well as moss. Available in several different forms, this makes an excellent base for a bioactive setup, or can be mixed with bark chips to create a forest floor type substrate.

ZooMed Eco Earth Substrate Block


The water holding ability of moss is amazing. Light when dry, it can be used to improve the moisture holding capacity of another substrate, or be used on its own in a moist hide for shedding or egg laying. Amazing stuff that takes a very long time to break down, and sphagnum moss in particular can inhibit fungal and bacterial growth.

ZooMed Terrarium Moss, Large 3.28L, CF-2L


There are several products available at the moment that are suitable to be used in a bioactive setup. They are designed so that you don’t have to make your own mix of soil, moss, coco fibre, and bark chips – just pour these over your drainage layer and you’re good to go!

ProRep Bio Life FOREST Substrate 10 Litre

The subject of substrate is a knotty one. There is a huge choice available – and different species have different requirements. We’re always available to answer your questions, and can help guide you to create the ideal living conditions for your pet!

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