To make a small terrarium, layer a LECA drainage base, activated charcoal, and a substrate barrier before adding soil. Select moisture-loving plants like Fittonia, seal the container, and allow the natural cycle of evapotranspiration to sustain the greenery.

As someone who has spent over a decade meticulously balancing the delicate chemistry of nano aquariums, I have found that the transition to terrariums is a natural and rewarding progression.

The same principles of biological balance and aesthetic design apply, but instead of managing dissolved oxygen, we focus on humidity and soil health.

Learning how to make a small terrarium allows you to bring a piece of the rainforest onto your desk, creating a self-sustaining world that requires far less maintenance than a traditional fish tank.

In my experience, the key to a successful build is not just the plants you choose, but the foundational layers you build beneath them.

Much like choosing the nano tank success depends on the right equipment, a terrarium’s longevity depends on its drainage and substrate.

Understanding the Two Main Types of Terrariums

Before we dive into the assembly process, you must decide which environment you want to simulate.

The choice between a closed or open system will dictate every other decision you make, from the species of moss to the frequency of your watering schedule.

Feature	Closed Terrarium	Open Terrarium
Humidity Level	High (80-90%)	Low (Ambient room humidity)
Plant Types	Tropicals, Ferns, Mosses	Succulents, Cacti, Air Plants
Maintenance	Very Low (Self-watering)	Moderate (Regular watering)
Biological Cycle	Relies on Evapotranspiration	Standard evaporation

For this guide, we will focus on the closed tropical system, as it offers the most fascinating biological processes to observe.

The Science Behind a Closed System

A closed terrarium functions as a miniature version of Earth’s water cycle.

Through the process of evapotranspiration, plants release moisture from their leaves, which then condenses on the glass walls and drips back down into the soil.

This constant recycling means you may only need to add water once or twice a year if the seal is tight.

I’ve noticed that many beginners struggle with “cloudy glass,” but this is actually a sign that your ecosystem is breathing and working as intended.

Essential Materials for Your Build

To learn how to make a small terrarium that lasts for years, you cannot skip the specialized materials that prevent rot and stagnation.

The Drainage Layer (False Bottom)

Since a glass jar has no drainage holes, excess water has nowhere to go.

I always recommend a LECA drainage layer (Lightweight Expanded Clay Aggregate) because it is porous, light, and provides a massive surface area for beneficial bacteria.

If you cannot find LECA, small aquarium gravel or river stones will work, though they are significantly heavier.

The Purification Layer

Above your drainage stones, you must include activated horticultural charcoal.

This layer acts as a chemical filter, absorbing toxins and odors that can build up in a stagnant environment.

In my experience, skipping charcoal is the number one reason why small terrariums eventually develop a “swampy” smell.

Pro Tip: When adding your charcoal, use a small spoon to create a thin, even layer. You don’t need a massive amount; just enough to completely cover the drainage stones and act as a barrier.

The Substrate Barrier

To keep your soil from washing down into the drainage layer and turning into a muddy mess, you need a substrate barrier.

You can use a fine plastic mesh, a piece of window screening, or even a thin layer of dried sphagnum moss.

This ensures the drainage layer remains “clean” and functional for the long term.

Step-by-Step Instructions: how to make a small terrarium

Now that we have our materials ready, let’s walk through the assembly process.

Step 1: Preparing the Container

Clean your glass vessel thoroughly with warm water; avoid using harsh soaps or chemicals that could leave a residue.

I prefer using glass jars with a gasket seal, as they hold humidity much better than loose-fitting lids.

Step 2: Building the Foundation

Start by adding 1-2 inches of your LECA drainage layer to the bottom of the container.

Follow this with a thin layer of activated horticultural charcoal.

Then, place your substrate barrier (mesh or moss) firmly over the charcoal.

Step 3: Adding the Growing Medium

Pour in a high-quality tropical potting mix, ideally one containing coco coir, orchid bark, and perlite.

Avoid standard garden soil, which is often too heavy and may contain pests or pathogens.

Pro Tip: Slope your soil from the back to the front. This creates a sense of depth and allows you to see the “ground” even when the front of the glass is partially obscured by plants.

Step 4: Planting Your Miniature Forest

This is the most creative part of learning how to make a small terrarium.

Use long-handled tweezers to place your plants, starting with the largest species in the back.

Ensure the roots are fully submerged in the soil and gently tamp down the surface to remove air pockets.

Step 5: The Final Mist

Use a spray bottle to mist the plants and the soil lightly.

You want the soil to be moist but never soaking wet; if you see water pooling in the LECA layer, you have added too much.

Choosing the Right Plants for a Small Space

Not every plant is suited for the high-humidity, low-airflow environment of a closed jar.

Just as you would select vibrant small aquatic species for a five-gallon tank, you must choose slow-growing terrestrial plants.

Fittonia albivenis (Nerve Plant) is perhaps the most iconic terrarium plant.

It loves high humidity and its striking leaf veins—available in white, pink, or red—provide incredible contrast.

For a ground cover, I highly recommend Selaginella uncinata, also known as Peacock Moss.

It has an iridescent blue-green hue that looks stunning under a dedicated LED grow light.

Other great choices include:

• Pilea involucrata (Friendship Plant)
• Syngonium podophyllum ‘Pixie’
• Various species of Nephrolepis (Lemon Button Fern)

Adding a Bio-active Cleanup Crew

One of the most advanced “secrets” of how to make a small terrarium is making it bio-active.

In the aquarium hobby, we use shrimp and snails to clean algae; in a terrarium, we use micro-fauna.

Adding a colony of Collembola (Springtails) is essential for a closed system.

These tiny insects eat mold and decaying organic matter, preventing fungal outbreaks.

For larger terrariums, you can also add Isopoda (Dwarf White Isopods).

They act as the primary decomposers, breaking down dead leaves into nutrients that the plants can re-absorb.

Maintenance and Troubleshooting Common Issues

Even a well-built system requires occasional monitoring to ensure the biological balance remains stable.

Managing Condensation

If the glass is so foggy that you cannot see the plants, there is too much moisture.

Simply open the lid for a few hours to allow some water to escape through evaporation.

Conversely, if no condensation appears in the morning, the system is too dry and needs a few sprays of distilled water.

Dealing with Mold

If you notice a fuzzy white growth on your plants, it might be Botrytis cinerea or another common mold.

This usually happens when there is dead plant matter and no springtails to eat it.

Remove the affected leaf immediately and increase the airflow for a day or two.

Trimming and Pruning

In a small container, plants can quickly outgrow their space.

Don’t be afraid to use small scissors to prune back aggressive growers; this encourages bushier growth and prevents the glass from becoming overcrowded.

Checklist for a Successful Terrarium Setup

To ensure you haven’t missed a step, follow this checklist during your build:

Task	Status	Note
Drainage Layer Installed	[ ]	Use LECA or gravel.
Charcoal Layer Added	[ ]	Prevents odors and rot.
Mesh/Barrier Placed	[ ]	Separates soil from drainage.
Tropical Substrate Added	[ ]	Slope for visual depth.
Plant Selection Planted	[ ]	Focus on moisture-loving species.
Springtails Introduced	[ ]	The “Cleanup Crew.”

Frequently Asked Questions

Do I need to use distilled water?

Yes, I highly recommend using distilled or RO (Reverse Osmosis) water.

Tap water contains minerals like calcium and magnesium that will leave unsightly white streaks on your glass as the water evaporates.

How much light does a small terrarium need?

Most terrarium plants prefer bright, indirect light.

Direct sunlight can act like a magnifying glass, overheating the interior and effectively “cooking” your plants.

A simple LED desk lamp or a north-facing window is usually perfect.

Can I add animals to a small terrarium?

In a very small container, you should stick to micro-fauna like springtails.

Vertebrates or larger invertebrates require much larger enclosures with proper ventilation and thermal gradients.

If you are interested in small living things, you might find that keeping small tetras in a separate nano tank is a better way to enjoy animal husbandry.

Why are my plants turning yellow?

Yellowing leaves are often a sign of overwatering or poor drainage.

Check the bottom of your container; if there is standing water above the LECA layer, you need to remove some moisture.

Final Thoughts on Creating Your Miniature World

Learning how to make a small terrarium is a deeply satisfying project that blends biology with art.

It provides a peaceful focal point for any room and offers a unique look into how ecosystems sustain themselves through evapotranspiration.

Whether you are an experienced aquarist or a complete beginner, the key is patience.

Allow the system time to stabilize, watch your Collembola work their magic, and enjoy the slow, steady growth of your indoor forest.

With the right foundation of drainage and charcoal, your small terrarium can thrive for many years to come.