What Is a Terrarium False Bottom? (And Do You Need One?)

I often like to say that a terrarium is a lot like building a house, but truth be told, that’s not entirely true.

You see, both houses and terrariums need a strong and stable foundation with good drainage (like us, plants don’t want to be swimming in water in their homes) but a house should divert excess water away from the foundation, and a terrarium towards.

It might seem counterintuitive, but a reservoir of water beneath our terrariums can provide a host of benefits for the ecosystem.

It’s ideal for plants that don’t like water around their roots, but truth be told, this approach works in all terrariums!

Let’s dig in.

Benefits of a False Bottom

  1. Provides a buffer so that your terrarium can balance any overzealous watering issues.
  2. Facilitates the flow of water around the terrarium – fueling the water cycle and keeping your plants watered for you.
  3. Reduces the risk of root rot and other problems associated with oversaturation of substrate by allowing water to effectively drain.
  4. Increases humidity by creating a supply of water to saturate the air. Great for tropical plants.

How to Create a False Bottom (The Drainage Layers)

As art imitates life, on our planet, the natural drainage function is fulfilled through groundwater

Where water seeps down to the bedrock and forms channels through fractures in the rock and spaces in the soil. That water is then channeled away till it feeds into rivers or streams – continuing the cycle.

The false bottom mimics this natural drainage mechanism in a terrarium.

1. Gravel or Stones (The Bedrock)

This layer is the foundation of your terrarium, and serves the purpose of the bedrock in channeling and storing water.

Whatever material you use, as long as they’re large and non-uniform in shape, they’ll naturally create spaces for water to collect. Plus, they should be strong enough to resist compaction and support the layers above it.

Some good choices are:

  1. River pebbles
  2. Glass beads or sea glass
  3. Aquarium gravel
  4. Activated charcoal pellets (more on that later)

You can also use specialised porous materials that are still tough and create space for loose water, but they also retain some. Thereby, increasing the amount of water you can store in the terrarium, e.g. leca clay balls

Finally, you can also use an egg crate – or some other strong grid-like layer – that can lift the contents of your terrarium away from the bottom of the container. 

Be careful not to make this layer too big. You want to create a place for water to pool when it needs to, but you don’t actually want a tonne of water sitting there. Otherwise something unwanted might develop in the stagnated water.

2. Activated Carbon (The Purifier)

As with any ecosystem, over time, toxins and gasses can build up in a closed terrarium if left without a way to deal with them.

It’s totally natural. Things die and decompose, but the resulting compounds can be potentially harmful to the plants… and pretty stinky for us.

That’s where activated charcoal/activated carbon can help. Activated charcoal is used in all kinds of filters and cleansers because it’s super reactive and loves to bind to toxins and impurities.

So, just like those charcoal tablets you can take for an upset stomach, a layer of activated charcoal can help to absorb those pathogens and aid in keeping your plants healthy and happy. 

You can buy activated charcoal in several forms, including fine powders and larger chunks

Activated charcoal for terrariums

So, whether you prefer to sprinkle some powder into your drainage layer or use larger chunks to make up the foundation – either way is effective.

3. Mesh/Screen or Fibrous Layer (The Substrate Barrier)

The final part of the puzzle is a barrier that works to guarantee separation from the substrate layer. 

After all, you don’t want any soil/substrate falling in between the cracks and clogging up your reservoir. Your drainage layer can only work if it’s kept clean and ready to receive water.

There’s generally two approaches to this problem.

  1. The natural approach uses a fibrous barrier of sphagnum moss (or something similar).
  2. The artificial approach uses a thin mesh or screen. There’s a variety of potential materials you can use here, but arguably the easiest and most effective approach is through a fibreglass screen like this one (just don’t choose a metal one that can rust).

There are advantages and disadvantages to both. A fibreglass screen is an unnatural element so it’s not to everyone’s taste visually, but if you cut and place it perfectly then you can minimise its visibility from the outside.

Whereas a sphagnum moss layer is natural, but needs to be much thicker to perform the same function. Plus, adding such a thick layer of absorbent material can significantly alter the flow of water through a terrarium.

Drainage Layers in Different Terrariums 

A false bottom is incredibly useful in just about every terrarium setup, but they can serve a slightly different purpose depending on your setup.

Open Terrariums

In open terrariums (e.g. succulent terrariums) there’s no water cycle to facilitate or humidity to regulate.

In fact, the likes of succulents and cacti typically don’t want any water around their roots, so the only job of that drainage layer is to allow water to freely drain away from the substrate. 

For this reason, false bottoms in open terrariums tend to be much larger and more straightforward. 

Vivariums

On the other hand, when it comes to vivariums, false bottoms can get technical real fast

The truth is, there’s an added level of complexity to keeping animals in a terrarium vs just plants. Often they get watered more regularly (especially if there’s an automatic misting system) and there’s additional needs in refreshing substrates for animals and such.

So, quite often drainage layers must be built with the ability to actually drain the drainage layer…

I say technical, it’s really just a little more hands-on on the DIY front. Here’s a great video by Tanner Serpa on how to create a drainable false bottom.

A Flexible Technique

Honestly, the false bottom process is pretty straightforward right?

Beyond the outlined steps, everything is exactly the same as a typical terrarium build.There’s plenty of flexibility in the model too, so you can adapt it to your needs. 

Realistically, any material can be swapped out, as long as the replacement performs the same function. The only truly consistent requirement is the order of the layers.

Though, as with all terrariums, exploring different options through trial and error is a big part of the process. This isn’t the only way to make a terrarium, but it might be the best way for you!

False Bottom Terrarium FAQ

How do you drain water from a terrarium?

If you have a false bottom in place, it’s difficult to drain a terrarium without disrupting the whole setup. It would be easier to simply open up your terrarium and allow it to dry out naturally. 

What is the best terrarium false bottom mesh?

There are a variety of branded terrarium mesh barriers, but they’re still fibreglass screens. You’re best off just buying a roll of standard fibreglass screen instead.

How deep should a terrarium false bottom be?

There’s no exact formula for the optimal depth of a terrarium false bottom (it depends on the size of your container) but it should be at least 1-2 inches to work properly.

Now it’s Your Turn

Do you follow the same process for your false bottom terrariums?

Everyone has their own ways of doing things and I’m sure terrarium making is no different.

Let me know in the comments.

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Hi! I’m Dan. Welcome to Terrarium Tribe. We’re a collective of people who love to build and care for natural plant terrariums. Join us!

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