This blog post is contributed by Sarah Gerrard Jones, an expert on houseplants.

A closed terrarium is a sealable glass vessel containing soil and plants.  Once water is added, and the container sealed, the terrarium becomes a self-sustaining mini eco-system. It is very low maintenance and perfect for people who can’t keep indoor plants alive.

Table of Contents:

Terrarium materials

To make your own mini jungle in a jar you will need:

  • Glass vessel – A Terrarium can be made from any glass vessel that has a lid but I would suggest that it’s best to use one made from clear glass, rather than coloured.
  • Gravel – Any washed gravel or pebbles will do.
  • Activated charcoal – This is optional but I suggest using it as it purifies the water inside the terrarium and helps remove odours. Activated charcoal can be found in Aquatic Shops or online.
  • Weed membrane or sphagnum moss – You can buy a weed membrane or sphagnum moss (used to line hanging baskets) from most garden centres or online.
  • Soil – Shop bought house plant potting soil, not soil dug up from the garden.
  • Plants – Be very careful when choosing your plants, not all plants like being in a humid environment, especially not Cacti and Succulents. These only do well in an open terrarium. Tropical ferns enjoy living in a closed terrarium as do Fittonia, Creeping Fig, Begonias, Moss and Baby Tears. Make sure and buy small varieties that stay small, so they don’t outgrow your terrarium in a few months. Ask advice from your local garden centre or plant shop.

How to make a terrarium

  1. Add your gravel or pebbles to the bottom of the glass vessel. This acts as a drainage layer, keeping the soil and roots of your plants away from the water which will gather at the bottom.
  2. Cut your weed membrane (or use sphagnum moss) so it fits snugly inside the vessel and place it on top of the gravel. This will ensure that the soil doesn’t fall through the gravel and create a bog at the bottom of the jar. 
  3. Add a thin layer of the charcoal
  4. Spoon in your soil on top of the charcoal. Think about how you would like your landscape to look?. Do you want it flat, sloping or perhaps add a hill to vary the height of the plants?
  5. Decide on where your plants will go and dig small holes in the soil. Remember to give each plant enough room to grow, so don’t place them too close to the glass. Next, remove each plant from its pot and gently massage the soil off the roots. Once you have removed most of the soil from the roots, place each plant into the soil, ensuring that the roots are completely covered with soil. Press each plant down gently so it stands upright.
  6. Add found objects like bark, twigs, pebbles and gravel
  7. Use a small paintbrush to gently clean the leaves of any soil
  8. Add water. This is best done with a spray bottle. Spray the leaves, the soil and the inside of the glass with just enough water that you start seeing the top 1-2cm of soil darken with moisture. Wipe the inside of the glass (to remove any soil) and put the lid on.

Caring for a terrarium

  • Water – observe your Terrarium, if it looks very wet, remove the lid for 24-48 hours to let it dry out a bit. Condensation should form on the inside of the glass – that’s a good sign that everything is working as it should. If you don’t ever see condensation forming you may need to add a small amount more water. 
  • Light – Your Terrarium needs light but never place it in direct sunlight. Go for somewhere that receives a medium amount of light, not too dark or too sunny.
  • Maintenance – If plants start to grow too tall, just nip the tops off with scissors. If you notice any leaves which have fallen on the soil, take these out to prevent them rotting and causing mould. If you do notice mould on the glass wipe it off and leave the lid off for a few days to dry it out. If you notice mould on the soil, use a fork to aerate the soil to improve drainage. Every few weeks take the lid off your Terrarium to allow fresh air to circulate.

Tips and takeaways

  • Choose a glass vessel with an opening wide enough to get your hand in. This makes it easier to make and maintain.
  • Rotate your Terrarium once a month to ensure the plants don’t start to lean towards the light
  • Don’t put your terrarium near a radiator or you’ll create a plant sauna which most plants won’t tolerate.

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Have you ever made a small terrarium of your own? What kind of plants did you put inside? Let us know in the comments below!

  • Last update: January 13, 2020

Posted in Garden Advice, Plants in the UK

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