Moss is close to the perfect material for greening a wall. It is light, needs no soil to speak of, asks for no feeding, and once established lives on shade, humidity and the occasional misting rather than a pumped irrigation system.
Living, not preserved
Be clear which you want. Much of what is sold as a "moss wall" is preserved moss: real moss treated so it stays soft and green but is no longer alive, used purely as decoration indoors. A living moss wall is a different thing, a genuine growing surface that needs the right conditions. This guide is about the living kind.
What it needs
Shade and humidity are everything. A living moss wall wants a spot out of direct sun, ideally north-facing or well shaded, with still, damp air. A bright bathroom, a shaded courtyard or a north wall all suit it; a sunny living room does not. Without enough humidity it browns and you are back to misting daily.
Building one
The usual approach is a shallow framed panel backed with a moisture-holding medium such as a felt mat or a fine substrate, onto which moss is pressed or grown in. Keep the panel evenly damp while the moss grips, using rainwater if you can. The slurry method works for covering an awkward shape: paint blended moss onto the backing and keep it misted until it knits. Once it has taken, the wall largely looks after itself in the right spot.
Indoors, and the humidity question
A living wall indoors lives or dies on humidity. Ordinary heated rooms sit too dry for moss to stay green, so an indoor living wall realistically needs either a naturally humid spot, a bright bathroom being the classic, or some help: regular misting, a nearby humidifier, or a sealed glass-fronted frame that holds moisture like a vertical terrarium. A room hovering around the upper half of the humidity range gives moss a fighting chance; a dry lounge does not. If you simply want green on the wall and not a maintenance habit, preserved moss is the practical answer, covered in preserved moss walls.
Watering without a flood
The trick with any vertical planting is wetting it evenly without water sheeting straight to the floor. Mist by hand for a small panel, or for a larger one fit a simple drip line along the top and let gravity carry moisture down through the backing. Whatever the method, the backing wants to stay damp like a wrung-out cloth, never running, and a waterproof tray or channel at the base catches the surplus. Rainwater keeps the moss greener and spares the wall the limescale that hard tap water leaves.