How to make a mini terrarium

*This guide was first released on Alice Magazine. You can find the original article in Danish here. All photos are taken by my sister Amalie Olofsson.

Terrariums are like small green houses with high humidity, and therefor the perfect climate for many tropical plants. They are decorative and actually very easy to care for as long as you find the right plants.

There are three types of terrariums; they can be closed, part closed or open. Closed terrariums create their own mini eco-system by reusing water and oxygen. You only need to add water a few times a year. In this guide I will show you step-by-step how to make your own closed mini terrarum.

What plants can I use?
First step is to find the right plants. Not all plants like it humid. Cacti for example don’t thrive in closed terrariums as they like it dry. However, tropical and sub-tropical plants are ideal plants as they love humidity. Plants that are small and slow growing, also thrive better than big and fast growin plants.

Always remember to choose plant of same needs. Do not put any succulents together with ferns. If in doubt it is always a good idea to ask your local plant pusher about what plants will thrive in closed terrariums.

What container can I use?
You can use any container you like. Only requirement is that they are clean, waterproof and light can shine through. A visit to your local second hand shop will give you lots of options for finding the perfect container. But keep in mind that containers with small openings are harder to plant than containers with large openings. To make a closed terrarium you will need to seal it.

Terrarium layers step-by-step

Step 1: Pebbles

Because terrariums don’t have drainage, you will need to make a layer of pebbles of 3-7 cm in the bottom. Drainage layers help ensure excess water doesn’t stay in the soil and cause root rot. Pebbles can be bought in most plant shops or in aquarium stores.

Step 2: Activated charcoal

Next layer is 1,5 cm of activated charcoal, which filters the air and water and keep the terrarium clean. You can buy activated charcoal in every aquarium store.

Step 3: Moss

Now you make a layer of moss for preventing soil moving down to the drainage layer. You may need to trimm the moss time to time if possible as it can grow several centimeters tall.

Step 4: Potting soil

25 % of the terrarium are now filled with drainage material and the next 25 % should be filled with potting soil. You can buy potting soil in every plant shop or in some grocery stores depending on the season. I have used soil mixed with perlite as it increase air circulation around the root system.

Step 5: Plants

At last you plant your terrarium. Make sure your plants are not sick, and remove any yellow or dead leaves. Trim the plants to the right size if necessary for them to be in the container.

How to take care of my terrarium?

Watering
After you finish planting your terrarium, water the plants and the potting soil with a spray bottle. If the opening is too small, add water with a teaspoon. The water must not go into the drainage layer, so you don’t need more than a few sprays. It is very important not overwatering, or the roots will rot.

How do I know if I have given the right amount of water?
If you see condensation on the glass the day after, you know you have given the right amount of water. If you can’t see the plants in the container, because of too much condensation, you might have overwatered.

You don’t need to water your closed terrarium more than a couple of times a year. Water only, when there is no longer condensation or if the plants are drying out. If you have given too much water, you need to take of the lid or open the sealing to increase air circulation.

Fertilizer
You don’t need to fertilize your terrarium un less your plants shows signs of nutrient deficiency, and you can see it is not because of need for water. Yellow leaves are often a sign of nutrient deficiency.

Light
Terrariums thrive best in indirect light. Don’t place your terrarium in direct sunlight as the increased temperature will overheat the plants and kill them. Always remember to choose plants with same need for light for your terrarium.

Trimming
Most terrarium plants will sooner or later need to be trimmed or removed, either they have grown too big or they have died. Before you trim, research your plant on how to trim it. Sometimes it is necessary start all over if the plants cannot be trimmed or be removed without breaking everything inside the terrarium.