Layering is a means of plant propagation in which a portion of an aerial stem grows roots while still attached to the parent plant and then detaches as an independent plant. Layering has evolved as a common means of vegetative propagation of numerous species in natural environments. Layering is also utilized by horticulturists to propagate desirable plants.

Natural layering typically occurs when a branch touches the ground, whereupon it produces adventitious roots. At a later stage the connection with the parent plant is severed and a new plant is produced as a result.

The horticultural layering process typically involves wounding the target region to expose the inner stem and optionally applying rooting compounds. In ground layering, the stem is bent down and the target region buried in the soil. This is done in plant nurseries in imitation of natural layering by many plants such as brambles which bow over and touch the tip on the ground, at which point it grows roots and, when separated, can continue as a separate plant. In either case, the rooting process may take from several weeks to a year.

Layering is placing one thing on top of another.

Layering in linguistics refers to one of the five principles by which you can detect grammaticalisation while it is taking place. The other four are: divergence, specialisation, persistence, and de-categorialisation.

Layering refers to the phenomenon that a language can have and develop multiple expressions for the same function, that language, in the “lexical” as well as in the “grammatical” domain, tolerates and permanently creates multiple synonymy. “Within a broad functional domain, new layers are continually emerging. As this happens, the older layers are not necessarily discarded, but may remain to coexist with and interact with the newer layers.” (Hopper 1991: 22)

During the process of grammaticalisation, new layers are added to older ones whereby the functional domain is broadened, i.e. several items may fulfil the same linguistic function.

An example from English: ‘I am going to study’ / ‘I will study’ / ‘I shall study’.

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