Moss makes the floor of a terrarium

Moss is what gives the woodland-floor impression. Without it, a terrarium stays an assembly of potted plants; with it, the ground becomes continuous and the landscape finds its scale. It also plays a practical part: it holds moisture at the surface, limits substrate splashing onto the glass when you mist, and gives a visual reading of the terrarium's state, moss turning brown says it is short of light or of water.

Our mosses are living and cultivated, never collected in the forest. That is a rule of the house, and it is also what avoids bringing moulds and pests into a closed environment.

Cushion, flat, or mossy stone

Cushion moss forms dense, domed mounds, perfect for suggesting hills or marking a foreground. Flat moss spreads out into an even mat and covers large surfaces; it is what gives the continuous ground. Mossy stone brings relief that is already formed, useful when you want a high point without building a mound. The species and their uses are set out in Mosses for terrariums: a short species guide.

Laying and looking after it

Moss is not planted, it is laid. Cut it to the shape you want with scissors, press it firmly onto an already moist substrate so that it takes hold, and mist. Contact is what counts: moss laid without being pressed lifts away and dries out. The full gesture is described in How to lay moss in a terrarium.

After that, it asks for two things. Indirect light: without it, the moss pales and then browns. And high humidity, so a closed terrarium, in open air it dries out within a few days. If it yellows or takes on a white veil, the causes are covered in Mould in a closed terrarium and Condensation in a terrarium.