A terrarium is the ultimate, low-maintenance indoor garden. Terrariums can be made out of any clear glass or plastic container, from the humble glass pickle jar to a specially made terrarium case. Their development is credited to Englishman Dr Nathaniel Ward, who invented a glass case – known now as the Wardian case – around the mid 1800s. Ward, who studied caterpillars and moths, was experimenting with a cocoon in a covered jar when he discovered that a fern had grown in the soil at the jar’s base.
Pick a container
Terrarium containers must be clear glass or plastic. You can use fish bowls, glass jars, jugs, vases or special terrarium containers. If you are using a closed container the cover should be transparent. Corks can be used for small openings in jars. Containers with large, uncovered openings can be used, but the humidity will not be as high as that in enclosed terrariums. In addition, unenclosed containers need to be watered more often. The container must be clean, or bacteria, fungi and algae will thrive. (Tip: never over-water a terrarium. It is better to have the terrarium too dry than too wet, as excessive water is very difficult to remove).
- Add a layer of gravel or small pebbles to the bottom of your container to assist with drainage. Cover this with a layer of charcoal (available from your local pet shop), to prevent the potting mix from becoming sour. Place a light layer of sphagnum moss over the top of the charcoal to prevent the potting mix from sifting down into the drainage area.
- The best growing medium for terrariums is a good quality commercial potting mix that has been sterilised. Unsterilised homemade mixes may contain fungi and algae, which will spoil the terrarium. The potting mix should be slightly moist when placed on top of the sphagnum moss. For most containers you will need a minimum thickness of 3.5cm (but go easy – too much potting mix spoils the look of a terrarium).
- You can reduce the root ball of plants in a closed terrarium by nearly half and it won’t harm plants, which can survive in this perpetually moist atmosphere with a reduced root area.
- When using plants of different heights, group the taller plants in the middle of the terrarium. After planting, mist spray to clean any potting mix sticking to the leaves or sides of the container. The water from the mist will be sufficient to provide moisture and settle the potting mix. Keep the container uncovered until the leaves are completely dry, then close it and enjoy your little world.
Many plants are suitable for terrariums. Moisture-loving houseplants from tropical and subtropical regions are ideal. Low-growing plants are preferred, but if using taller plants, pinch back their tips occasionally. Choose plants that have similar temperature, light and water requirements.
Don used African violets (Saintpaulia spp.), baby’s tears (Soleirolia soleirolii), silver net plant (Fittonia verschaffeltii var. argyroneura ‘Minima’), peperomia (Peperomia cv.) and parlour palms (Chamaedorea elegans, sometimes sold as Neanthe bella). Other suitable plants are Pilea spp., sygoniums, begonias, crotons, dracaena, small ferns and the polka dot plant or freckleface (Hypoestes). You can use baby’s tears, bush moss or club moss as a groundcover. Add pebbles, rocks or driftwood as accessories.
Once established, a terrarium will need only minimal maintenance. This simply involves checking that the light and moisture levels are adequate, and perhaps pruning any overgrown plants.
Place your terrarium in a brightly-lit spot. Several feet from a window is ideal, but don’t put it in direct sunlight. If plants appear healthy and are growing straight and symmetrically, then the light level is sufficient. Periodic turning of the terrarium will prevent plants from becoming lopsided.
A closed terrarium may not need watering for several months, as plants recycle moisture. If the potting mix looks dry or plants start to wilt, water with a mist spray. If water condenses heavily on the glass inside the container, you have added too much water. In this case, remove the lid for several days to allow excessive moisture to evaporate.
Fertilising is not necessary for at least a year after planting. If leaves become yellowish and lack vigour, fertilise very lightly with a water-soluble solution at one-tenth the rate recommended for normal houseplants. Terrariums with an open top will require more frequent watering.
Glass terrariums similar to the one Don used cost around $50-$80 from Lincraft. Charcoal costs about $6 for 500g, and sphagnum moss cost about $12-$15 for a 5 litre bag. The plants used in our terrarium are readily available from nurseries, and cost $6-$10 for 100mm (4″) pots. For more tips on terrariums, see Cheryl Maddocks’ article in the August edition of the Burke’s Backyard magazine, available from newsagents and supermarkets for $5.50.