Moss asks for the opposite of most gardening: poor soil, shade, damp and patience. Give it those and it will largely look after itself. Here is how to start.
1. Pick the right spot
Shade and moisture are everything. North-facing walls and beds, the foot of trees, shaded paving and damp stone all suit moss. Strong sun and dry wind are the enemies; a spot that bakes by midday will defeat you whatever you do. If the surface stays cool and a little damp for most of the day, you are in business.
2. Lower the competition
Moss is a poor competitor against grass and weeds, so it wins where they struggle. Clear off existing growth, then firm the surface and, on most soils, nudge it towards acid. Bare, compacted, slightly acidic ground suits moss far better than the rich, fluffy loam we lavish on everything else. Do not add compost or feed.
3. Transplant, or make a slurry
The direct way is to lift fresh patches of moss and press them firmly onto the prepared surface, peat side down, with good contact all over. Keep pieces small and butt them together; they knit in time.
The other way is the slurry, or "moss milkshake". Blend a couple of handfuls of clean moss with enough buttermilk, natural yoghurt or plain water to make a thin paint, then brush or pour it onto stone, brick, pots or shaded soil. The moss fragments regenerate where they land. It looks unpromising for a few weeks, then greens up.
4. Keep it moist while it takes
For the first three or four weeks, mist daily, ideally in the morning or evening rather than the heat of the day. This is the make-or-break stage while the rhizoids grip. After that, in a properly shaded spot, rainfall and shade usually carry it.
5. Then leave it alone
No feeding, no digging, no mowing. In autumn, sweep or gently blow off heavy leaf litter so the moss is not smothered over winter. That is the whole maintenance regime. The cushion thickens year on year.
Choosing the right moss to start with
Match the moss to the job. For fast, continuous cover over ground or a wall, use the creeping carpet-formers, the pleurocarpous mosses such as the plait and feather mosses, which knit together quickly and fragment readily for slurry. For cushiony texture in a terrarium or a moss garden, use the upright acrocarpous mosses such as bun moss and the fork-mosses, which hold a domed shape but spread slowly. The easiest moss to start with is whatever already grows happily in your own garden, because it is proven to suit your conditions; lift a little and propagate from that rather than importing something that may sulk. See acrocarpous and pleurocarpous mosses for the distinction.
Growing on different surfaces
The method shifts a little with the surface. On soil, clear competition, firm it hard and press moss into good contact. On stone, brick and concrete, the slurry method works best, painting blended moss onto the porous surface in shade. In pots and on bonsai, a thin pressed layer keeps the surface cool and finished; see moss for bonsai. On a wall or vertical panel, you need a moisture-holding backing and patience, as in living moss walls. The constants across all of them are shade, damp and firm contact; the rest is detail.
The slurry method in more detail
The slurry, or "moss milkshake", is the workhorse for covering an area or an awkward shape. Blend two or three handfuls of clean moss with enough liquid to make a thin, brushable paint. The classic binder is buttermilk or natural yoghurt, which helps it cling and feeds the moss a little, though plain rainwater works and avoids the faint smell while it establishes. Brush or pour it where you want growth, keep the fragments coarse rather than pureed so more of them survive, and mist daily. It looks unpromising for a few weeks, then greens up as the fragments regenerate. For a whole wall, the same mix can be sprayed, as in spraying moss slurry at scale.
The common mistakes
Three errors account for most failures. The first is choosing too sunny or dry a spot, which no amount of care overcomes; shade and moisture are not optional. The second is enriching the ground, since compost and feed help the competition, not the moss, which wants poor, firm, slightly acidic ground. The third is giving up too soon: moss is slow, and a patch that browns in a dry spell is almost always dormant rather than dead, so water it and wait rather than digging it out. Get the spot right and resist fussing, and moss is one of the most self-sufficient things you can grow.