What are layering and division?
Two propagation methods that avoid the difficult part of taking cuttings, because the new plant stays attached to the parent or already has roots.
Layering. A stem is encouraged to root while still attached to the parent plant, which continues to supply it with water and nutrients throughout. Only once roots have formed is it separated.
Why it succeeds where cuttings fail. A cutting must survive on stored resources while producing roots, and desiccation kills most failures. A layer has no such problem — the parent sustains it, so there is no race against drying out. This makes layering the most reliable method available, and it is how plants that are notoriously difficult from cuttings are propagated.
Simple layering. Bend a low, flexible stem to the ground, wound the underside slightly, peg it down, and cover with soil, leaving the tip exposed. Leave for a season or more, then check for roots and sever.
Serpentine layering does this several times along one long stem.
Tip layering, where the tip is buried, which brambles do naturally.
Air layering, for plants with no low stems — a section of stem is wounded, wrapped in damp moss and enclosed in plastic, and roots form within the wrapping. Used for houseplants that have become leggy, and for trees.
Mound layering (stooling), for fruit rootstocks.
Division. Lifting a clump-forming plant and separating it into pieces, each with roots and shoots.
Why it is the easiest method of all: each division is already a complete plant, so establishment is nearly assured.
When to divide: generally when the plant is dormant or growing slowly — spring or autumn for most herbaceous perennials, with the general guidance being to divide spring-flowering plants after flowering and later-flowering ones in spring.
How: lift the whole clump, separate by hand, with two forks back to back, or by cutting through with a spade for tough clumps. Discard the old, woody centre — the vigorous material is at the outside — and replant the divisions promptly and water in.
It rejuvenates the plant as well as multiplying it, which is why congested clumps flower poorly.