What is a terrarium?
A terrarium is a miniature garden laid out in a transparent container, ideally glass. This technique was much in vogue in Victorian times, and remains highly popular.
Depending on the gardener’s imagination, the terrarium can take on the appearance of a woodland scene, a tropical jungle, an enchanted forest, and so on. You can even add water, insects or small animals and turn it into a vivarium.
A small-scale ecosystem
Creating a terrarium is an interesting and educational project, for it clearly illustrates how an ecosystem works, but on a reduced scale. Many different processes occur and interact: photosynthesis, respiration and the water cycle, among them.
Moreover, in a closed terrarium the water is constantly recycled, passing from liquid form to gas. We therefore get to see the water cycle: the moisture sent into the air by leaves during transpiration condenses on the glass walls, returns to the soil and is absorbed by the plants’ roots. And the cycle begins anew.
Growing plants or in a terrarium is an original way of coping with the problem of the dry air in our homes, since it provides a very humid environment for plants, making it possible to grow more demanding varieties such as insectivores.
A terrarium for succulents?
It’s best to avoid growing cacti and other succulents in terrariums (often called “dry terrariums” or “desert terrariums”), although this practice is very popular. As it happens, the conditions that prevail in terrariums (damp and poorly ventilated atmosphere, soil that remains moist for a long time) are not suitable for the needs of these plants from arid environments. Rot is likely to set in, even in an open terrarium.
As well, although most succulents require intense light, a glass-enclosed garden shouldn’t be placed in full sun because the temperature will get too high. For all these reasons, if you wish to compose a small arrangement of succulents, it’s best to use a low container with drainage holes.
Container and materials
The originality of a terrarium depends on the type of container you use, the plants you choose and the way you arrange them.
Any glass container can serve as a terrarium, provided that it is transparent and not tinted. You can recycle a large glass jar, a fish bowl or an old aquarium. For ease of assembly and maintenance of the terrarium, it is preferable to choose a container with an opening large enough to comfortably fit your hand through.
It doesn’t take much to set up a terrarium:
- fine gravel, coarse sand, or clay beads for drainage;
- charcoal chips to help absorb odors;
- a piece of window screen or permeable geotextile to act as a soil separator;
- potting mix appropriate to the plants used;
- decorative elements such as bark chips, stones, moss or driftwood.
Some people omit the drainage layer and the charcoal chips and still get good results.
Commercial potting mixes for indoor plants can be used with most tropical plants.
For the cultivation of insectivorous plants, however, use an acidic substrate. For example, a mixture of equal parts peat moss and a lightweight material such as perlite, Chabasai or Turface is suitable for Drosera and Pinguicula. For Nepenthes, a lighter and airier substrate consisting of sphagnum moss and conifer shavings (such as those used for orchids) is more suitable. Other substrate recipes can also be used.