Structure goes in before the plants

In a successful terrarium, what catches the eye is almost never a plant: it's a root running across the frame, a stone creating some relief, a line of sand suggesting a path. These elements go in first, on the levelled substrate, before any planting at all. Once the plants are in place, it becomes very hard to correct the composition without pulling everything apart.

Driftwood and roots

Wood provides the vertical lines and movement. A root placed on the diagonal makes a small container look bigger visually; two parallel roots flatten the scene. Choose wood that's dry, hard and free of bark: bark breaks down under glass and feeds mould. In a closed, humid environment, a fine white fuzz can appear in the first few weeks on new wood, this is a harmless surface fungus, which the microfauna of a bioactive soil eats away, and which our mould guide teaches you to tell apart from a real problem.

Stones and minerals

Dark, porous stones, such as volcanic rock or lava rock, pair well with mosses, which eventually colonise them. Avoid limestone, which leaches out and shifts the pH. A simple rule of composition: an odd number of elements, clearly different in size, never lined up.

Sands and gravels

A pale sand on the surface marks out a path or a bank and stands out against the darker substrate. Use it on the surface only: mixed into the substrate, it compacts it and blocks drainage. To see the full method applied to a project, take a look at A miniature forest under glass.