Carnivorous plants exist in fascinating shapes and forms, all having evolved carnivory as a means to cope in low-nutrient environments. Not surprisingly, carnivorous plants appeal to many people as houseplants. Because they often have strict light and humidity requirements, terrariums offer a way to display carnivorous plants while meeting their needs.
Carnivorous plants grow in a variety of habitats found around the world, so a single environment cannot meet the needs of all species. However, terrariums allow the carnivorous plant enthusiast to control light, temperature and humidity in order to grow species that have requirements beyond what can be provided in the open as a houseplant. Terrariums also make it easier to flush and siphon salts from the growing medium.
Terrariums have clear covers that allow access to light and can be opened or closed to ventilate the inside. The carnivorous plant nursery Botanique recommends including a small well at the back of the terrarium so that, monthly, excess water can be siphoned and salts removed from the growing medium. The type of light and growing medium depends on the plant's needs. Some terrariums may be enclosed in a reflective material on all but the top and viewing side in order to maximize plants' exposure to light.
Barry Rice of the International Carnivorous Plant Society recommends adapting an aquarium for carnivorous plants rather than buying a glass container specifically sold as a terrarium. Aquariums are constructed so that they don't leak, which is not the case for all terrariums. Plants can be planted directly into the growing medium or grown in individual pots. Rice recommends the latter if you plan to propagate your plants because they are easier to remove. If aesthetics concern you, the pots may be buried in growing medium or covered with sphagnum moss.
When planning your terrarium, Botanique recommends choosing plants that have similar needs. Once you've established your terrarium, monitor the temperature and observe whether the glass is fogging up. If it is, it might be too hot and humid. Unless you are growing plants that require those conditions, you might need to provide more ventilation in the lid. Barry Rice also recommends installing a small fan similar to those used to ventilate computers to improve air flow around your plants.
Be careful when watering your terrarium plants, and do not splash water on the leaves. As Botanique points out, the high humidity in most terrariums prevents drying, which increases the chance of disease. If plants are in individual pots, water them individually and with enough water to soak the growing medium and leach out any accumulating salts.