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 this approach works in just about all terrariums!

Let’s dig in.

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False bottoms may be a simple concept, but they come with plenty of potential benefits.

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 an 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.

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 terrarium layers above them.

Some good choices are (links to Etsy):

1. River pebbles
2. Glass beads
3. Sea glass
4. Aquarium gravel

You can also use specialized 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 (though it’s hard to quantify just how much). 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 – see it on Etsy.

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

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 are 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 fiberglass screen like this one (just don’t choose a metal one that can rust).

There are advantages and disadvantages to both. A fiberglass 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 minimize 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.

• See preserved sphagnum moss on Etsy.

Ultimately the choice comes down to personal preference.

Though they both have their advantage, when done right they should both serve their function just fine.

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

Open Terrariums

In open terrariums (e.g. a succulent terrarium or cactus terrarium) 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 are additional needs for refreshing substrates for animals and such.

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

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!

In my build for the Essential Guide to Tropical Terrariums, I opted for a drainage layer but as I don’t like unnatural elements in my terrariums (like a mesh screen), I paired it with a substrate with lots of sphagnum moss.

So you don’t necessarily NEED a mesh screen or fibrous layer to have a functioning false bottom if your substrate is super spongy as it won’t fall through the gaps.

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.