Top tips for keeping a terrarium The growing medium, which should be very free-draining at the base, can be layered in textures. Add a little crumbled charcoal to keep the soil sweet. Terrarium gardeners soon learn how to adapt tools for working in confined spaces. Long tweezers without too much spring, tiny forks or trowels taped to bamboo canes, chopsticks, a length of hose and a funnel to add composts and grit, all are simple to obtain or make. Always keep plants which need special conditions together. Don't try mixing drought-loving succulents with moisture-loving ferns, for example. Once plants have established they need little maintenance. In enclosed spaces the moisture should recycle. Trial and error will establish when plants need any extra water. Remove any dead or dying foliage immediately to reduce the chance of fungal diseases. Prevent foliage from touching the glass sides. Ken Marten is a terrarium-maker and founder of Hermetica