An Introduction to Bioactive Terrariums

A naturalistic way of keeping reptiles, amphibians and invertebrates with live plants

If you’ve been following our articles or blog, you will have heard us use the term ‘bioactive’ – usually followed by ‘but that’s too large a subject to go into here’. So we thought it was about time that we went into more detail about this exciting, naturalistic way of keeping reptiles and amphibians that’s finally seeing a lot more popularity – and rightly so!


So what do we mean by ‘bioactive’?

The dictionary definition of bioactive is: ‘(of a substance) having or producing an effect on living tissue’.

What we take it to mean is a system that resembles the living ecosystems that the ancestors of our pets first came from, and that their wild relatives still inhabit. It’s a way of using the entire environment to provide a home for our pets that’s as close to nature as possible, and one that takes care of itself to a greater or lesser degree.

The biggest element of the bioactive environment is, of course, the substrate. Get that right, and the rest of it works well from the very beginning.


Where do I start?

Assess the housing that you are about to start assembling your living substrate in. What animal is going to be living in it? Is the housing wooden or glass? Wooden vivariums are somewhat more problematic, as by its very nature the substrate needs to be damp, and wooden vivs do not like to be damp.

This problem is not, however, insurmountable. You can either seal the wood using something like waterproof yacht varnish – works well but do make sure it is thoroughly aired out – or line the vivarium with something waterproof. Glass, perspex, or even pond liner can be used; if fixed with aquarium grade silicone sealant, this will effectively and safely waterproof your wooden viv.

Be warned: a glass lined vivarium is astonishingly heavy!

We will use, as an example, a glass terrarium being assembled for tropical forest geckos – Crested, Gargoyles or day geckos, or a colony of mourning geckos.

Certain areas of the internet like to use glass aquariums, and these can certainly be pressed into service. Unfortunately, as they were designed to hold water, they do not allow for very good ventilation at the bottom. Damp + poor ventilation = problems! Anaerobic bacteria can get hold at the bottom of the damp area, nothing can live in it, and you begin to get an area that not only smells bad, but can be a threat to the health of your pet. So no aquariums, please – in this day and age there are far better alternatives to use!


OK, I have a well ventilated glass box. Next step?

The most important part of the living system is the substrate – your forest floor. This is the powerhouse that will turn waste into plant food, keep your plants and animals healthy, and regulate humidity.

We don’t want our plants to be sitting with their feet in water (this can cause rotting), but ideally we want a small reservoir under the substrate to keep it moist. To achieve this, we use a drainage layer, in the same way that when you put plants in a pot you include bits of broken plant pot to help the soil drain.

This drainage layer can be gravel, any other granular substance that doesn’t rot, or expanded ceramic balls. These are lightweight and provide a huge surface area for bacteria to colonise, which will help to detoxify liquid waste that trickles down to the bottom. These ‘good’ bacteria turn harmful compounds into harmless ones that plants can use as food, in exactly the same way that the filter on a fishtank does.

Layer your drainage material fairly generously, then lay a barrier on the top of it to prevent substrate working its way down between the grains and clogging the whole system. Terrarium fleece or  mesh allows liquid through freely, but is fine enough to prevent substrate getting through.

Once your drainage layer is installed and sealed, then it’s time to add substrate. 

You want to replicate tropical forest floor, so you need a good base. If you don’t want to mix your own, there are some excellent pre mixed substrates out there these days; they are probably the best way to start if you haven’t gone bioactive before. The ideal substrate holds water but is free draining, has a variety of grain sizes to prevent compaction, and is slow to break down.

This can be achieved by mixing coir fibre, orchid bark, cork bark litter and moss in varying quantities – or you can just buy a bag of ready mixed substrate!


We have our base layer, right?

On top of this, if you can, should go a generous layer of leaf litter. You can buy Pete’s Bio Active Leaf Litter, or collect your own; oak, beech, magnolia, sweet chestnut, horse chestnut, mulberry, hawthorn, birch, poplar and sycamore are all commonly used. If you collect your own, take them from the ground after they have fallen – the tree has removed everything it needs from them, making them safe to use. Make sure you are away from roads, and any areas where unwormed dogs and cats might have used them for a toilet!

As these leaves rot down they will add important substances and micronutrients to the soil that both your plants and your clean up crew will very much appreciate. If you are collecting from the wild, you will also be adding beneficial bacteria from the forest floor that will help the natural action of your substrate.

Now it’s time for the next step – introducing the clean up crew.


What’s that, then?

Your clean up crew do all the heavy lifting in the bioactive system! They break down solid waste into a form that allows the beneficial bacteria to get to work on it, reduce your piles of leaves to the lovely rich humus that your plants will appreciate, and are an interesting spectacle in their own right.

Springtails, woodlice – tropical and native – earthworms, small millipedes, and even mealworms are all used.

Springtails are tiny, pale coloured arthropods that live in and feed on decaying matter. They are instrumental in keeping your substrate in good order; if you turn over a clump of decaying leaves in the woods, they’re the tiny creatures that bounce away from the light. They will break down waste matter, and help to stop moulds and fungi from taking over the substrate.

They can be bought as cultures ready to add, and you can also buy extra food for them to help build their numbers up when they are first introduced.

Earthworms keep the substrate turned over and aerated, as well as taking their own share of leaves and other waste matter.

Woodlice, again, eat decaying matter (especially wood and leaves), and should your vivarium inhabitant eat them they won’t be harmed – in fact, as the shell contains a high level of calcium, it can be very beneficial!

Mealworms are omnivorous, and have a bad reputation for nibbling on vivarium inhabitants. However, when they are part of a living substrate there is plenty for them to eat, and they do appear to prefer to eat whatever they can find that isn’t moving.

If you have collected your leaf litter from the wild, you may well find that you have introduced other small invertebrates to the system – tiny snails, millipedes, and soil mites. These will all take their place in the soil community you have created, and really contribute to the effectiveness of your living substrate.

Once you have added all your clean up crew, you’re ready to start planting and adding branches – which we will cover in the next article!

Animal Information

We have been using bioactive set ups in our shop for a number of years.