Creating layers in a terrarium is an art that involves careful consideration of various elements. Each layer serves a specific purpose and contributes to the overall health and aesthetics of the miniature ecosystem.

1. The Drainage Layer

The first layer, known as the drainage layer, is essential for preventing waterlogged soil. In the past I have used small pebbles for this layer, but since finding out the many benefits of Leca Clay Balls, I wouldn’t use anything else. But you can use small pebbles or scoria if you wish.

You may already know about Leca Balls being used as a soil-less medium for house plants. However, they are the perfect solution as a drainage layer in your terrarium. If you’re wondering why they are called LECA… it stands for Lightweight Expandable Clay Aggregate.

The benefits of LECA are many:

The clay balls absorb water from the bottom up, yet remain full of oxygen at the same time thanks to all those tiny bubbles of air created when the clay was baked, While allowing for drainage, LECA retains some moisture, contributing to more consistent humidity levels in the terrarium.

As well as being eco-friendly, LECA is very light-weight, so less likely to crack the glass and easier to move your terrarium around.

LECA balls are affordable and reusable. You can use LECA balls over and over again, even forever if you maintain and clean them properly before reuse in a new terrarium. Because LECA does not decompose, it's nutrient system and aeration quality does not change over time.

LECA is readily available in New Zealand at your local garden shops, Mitre10 and Bunnings.

 2. Separation Layer

In a terrarium, a separation layer plays a crucial role in maintaining the overall health and functionality of the ecosystem. The separation layer is typically placed between the drainage layer and the substrate or growing medium.

The primary purpose of the separation layer is to prevent the substrate or growing medium from mixing with the drainage layer. This helps to maintain proper water drainage and aeration within the terrarium, preventing waterlogging and root rot.

The separation layer also aids in keeping the terrarium clean and organised. It acts as a barrier, preventing any debris or organic matter from sinking into the drainage layer. This ensures that excess moisture can easily pass through while keeping the upper layers free from clogs or blockages.

I personally use a black weed mat cut in a circle to the width of the terrarium, but various materials can be used including horticultural fabric, fine mesh screens, or fibre-glass mesh. These materials allow water to pass through while effectively separating the layers.

By incorporating a well-designed separation layer in your terrarium setup, you can create an optimal environment for plant growth while ensuring proper moisture regulation and preventing potential issues associated with poor drainage.

 3. Sphagnum Moss

A layer of Sphagnum Moss serves two purposes placed as your third layer. It benefits by retaining moisture which helps to maintain humidity levels within the enclosure, and also works as another separation layer to avoid leakage of substrate into the drainage layer.

 

4. Activated Charcoal

Activated charcoal is a must in any sealed terrarium. In fact, I add it to all my terrariums, whether sealed or open, on top of the Sphagnum Moss. Its primary function is to filter out impurities and odours, keeping the terrarium environment clean and fresh. Activated charcoal also helps prevent bacterial growth.

Activated Charcoal is available in granule or powder forms, the latter being much messier to apply if not done correctly.

5. Terrarium Substrate Mix

The substrate layer comes next and it’s really important to get this right! Think of it as the heart of your terrarium, that feeds and nurtures your plants needs. The substrate needs to achieve the correct baIance of water retention, drainage, aeration, and provide support to growing plants.

It is essential that you choose a well-draining substrate specifically formulated for terrariums. This will help maintain proper moisture levels and prevent root rot. For best results, your substrate should be soil-less, light and fluffy.

My Preferred Substrate Mix

Coir (Base)

My absolute favourite as the core of my substrate mix! Coir is derived from the husks of coconuts and highly valued for its excellent water retention properties, making it an ideal, natural choice for terrariums. It has the ability to hold moisture while still providing good drainage and aeration, preventing waterlogged conditions that can be detrimental to plant health.

Additionally, coir is known for its natural resistance to pests and diseases, making it a safe and sustainable option for terrarium setups.

Coir blocks are readily available at local garden centres. When using coir, it is important to properly prepare it by soaking and rinsing it thoroughly to remove any excess salts or impurities. This ensures that the substrate is clean and ready for use in the terrarium.

Its natural properties make it an excellent choice for creating a healthy and thriving environment within your terrarium.

+ Pumice (Aeration & Drainage)

Pumice provides the aeration and drainage elements required in terrarium substrates. Pumice is an all-natural,100% ORGANIC growing medium that provides an ideal balance of moisture retention, gas exchange, and draining capabilities. Not only does it come directly from the earth, it stays in its raw form.

Each individual pumice stone has countless microscopic pores that each act as little sponges, storing the nutrient-rich water, later releasing it when the soil needs hydrating.

Using pumice in your terrarium substrate mix brings oxygen to the root zone, allows carbon dioxide to escape, enables air circulation, and makes food and water consistently available for root uptake.

Again, pumice is readily available and affordable at your garden centres, Mitre10 and Bunnings.

+ Sand (Aeration & Drainage)

Sand is a low cost, easy way to add aeration and drainage to your substrate. Course propagation sand is best and definitely not sand from the beach!

Propagation Sand is readily available at your garden centres, Mitre10 and Bunnings, usually in two grades; fine and course. I use the fine grade as it’s more aesthetically pleasing than having larger clumps of white stone in your substrate mix.

+ Earth Worm Castings (Nutrients & Fertiliser)

Because Coir contains no nutrients, you will need to add an an organic element to your terrarium substrate.

Worm castings, also known as vermicompost, are the rich organic matter (poop) produced by earthworms during the decomposition process. They are highly beneficial for terrariums due to their nutrient-rich composition and ability to improve soil structure.

When used as part of a terrarium substrate, worm castings provide essential nutrients such as nitrogen, phosphorus, and potassium that plants need for growth. These nutrients are released slowly over time, ensuring a steady supply of nourishment for the plants.

In addition to their nutritional value, worm castings also enhance soil fertility by improving its water-holding capacity and drainage. This helps prevent overwatering or waterlogged conditions within the terrarium, which can be detrimental to plant health.

Furthermore, worm castings contain beneficial microorganisms such as bacteria and fungi that contribute to overall soil health. These microorganisms help break down organic matter further and aid in nutrient absorption by plant roots.

Overall, using worm castings in your terrarium substrate can significantly enhance plant growth and create a thriving ecosystem within your enclosed environment.

6. Hardscape

Placing larger rocks can provide a center-piece and also help to landscape hills, slopes or stepped layers to create a visual effect.

7. Plants

Now it’s time to add your carefully selected plants suited to a closed terrarium. You will find an extensive list of suitable plants in my last blog 'Selecting the Right Plants for Your Terrarium'.

Ensure that you choose plants that have the same requirements. ie. light, water and humidity. Don't mix succulents and tropical plants together as they have totally different needs. Succulents will not survive in a closed terrarium as they need sunlight, require less frequent watering and won't survive the humidity of a closed terrarium.

I find it easier to place plants on the outer sides of the vessel first and then work in the centre. However, it does depend on the shape of your terrarium vessel.

8. Living Moss (optional)

Living moss looks amazing in sealed terrariums, creating a real forest vibe. There are several different mosses available. We are lucky enough to live in the bush, so I am able to collect my own.

If you do go moss hunting, be sure to bring it home and soak it in water to ensure there are no ‘hangers on’ come home with you! You don’t want to be adding unwanted bugs to your terrarium. Although you can add Isopods and Springtails which are very beneficial to clean up your eco-system. But to be honest, I don’t like seeing bugs in mine.

If you don’t have access to living moss, it is available online and in some garden centres.

8. Decorative Pebbles & Enhancements

Finally, decorative pebbles or small rocks can be added as a top dressing to enhance visual appeal and provide stability to taller plants. These decorative elements also help keep substrate in place. You can mix it up by placing a few larger pebbles in a mound, with smaller pebbles surrounding it. You can also use sand (not from the beach) in some areas and pebbles in others.

You may want to add miniature decorations such as a crystals, park bench, mushrooms, animals, fairy houses, fairies etc. You can find a lot of miniature options on Temu and Aliexpress.

By carefully constructing these layers, you can create an ideal habitat for your terrarium plants while adding beauty and depth to your miniature garden.