Layering is the process where stems that are still attached to the parent plant form roots at the point where they touch a rooting medium (soil / compost)
When the rooted the stem is severed from the parent plant and becomes a new plant.
This method of vegetative propagation usually gives a high success rate because the cutting is still part of the parent plant as it roots, and is not subjected to the stresses that other types of cuttings may undergo.
Some plants layer themselves naturally, whereas others may require some manual intervention.
Simple layering;
Select suitable strong shoots / stems and bend them down to the ground.
Form shallow holes in the soil where they are to be pegged down.
Fork up the base of the hole then place some sharp sand or grit in the bottom.
Make a shallow incision on the underside of a leaf node with a sharp blade and dust the wound with hormone-rooting powder.
Peg the shoot down, cover with compost and keep the area moist.
Alternatively; use a sunken pot / tray filled with compost as opposed to layering into a hole.
Serpentine layering;
This is basically the same as 'simple layering but as opposed to pegging down one leaf node, you can peg down as many nodes as you can along the same stem.
Tip layering;
Often used with fruit trees such as blackberries.
In late summer select healthy shoots that have been produced that season and that can be readily bent down to a convenient spot beneath the plant.
Excavate a 150mm (6”) deep hole with a hand trowel; make one side sloping towards the parent plant.
Secure the shoot tip (snoot) with a wire peg or stone before filling in with soil.
The layer/s should be well rooted by winter.
After rooting sever it from the parent plant leaving about 300mm (12”) of old cane still attached, over-winter it in a cold frame.
Transplant severed layers in early spring.
An alternative method is; do all as above, but layer into a pot of compost as opposed into a hole.
Compound layering;
Often used to propagate Rhodendrons and Azaleas.
Choose low-lying stems and remove any leaves that would be buried when they are pegged down.
Make a shallow incision on the underside of the stem with a sharp blade and dust the wound with hormone-rooting powder/gel.
Loosen soil below the shoot and add lime-free sand to aid rooting.
Peg the wounded section of the stem down into a shallow hole, and then carefully tie the tip as upright as possible to a support stake without snapping the stem.
Cover with soil and keep moist.
Alternatively; layer into a sunken pot filled with compost rather than forming a hole.
Mound (stool) layering;
Often used when propagating gooseberries and apple rootstocks.
Cut the plant back to 25mm (1") above the soil in the dormant season.
Mound soil / compost over the emerging shoots in the spring to enhance their rooting.
Air layering;
Air layering is used to propagate some indoor plants with thick stems, or to rejuvenate them when they become leggy as described 'here'