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Aerial stem – A stem with an erect or vertical growth habit above the ground.

Layering is a means of plant propagation in which a portion of an aerial stem grow 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 utilised by horticulturists to propagate desirable plants. Natural layering typically occurs when a branch touches the ground, whereupon it produces adventitious (appearing in an abnormal or unusual position or place) 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 more complicated than taking cuttings, but has the advantage that the propagated portion can continue to receive water and nutrients from the parent plant while it is forming roots. This is important for plants that form roots slowly, or for propagating large pieces.

Ground layering

Ground layering is the typical propagation technique for the popular Malling-Merton series of clonal apple rootstocks in which the original plants are set in the ground with the stem nearly horizontal, which forces side buds to grow upward. After these are started the original stem is buried up to the tip. At the end of the growing season, the side branches will have rooted, and can be separated while the plant is dormant. Some of these will be used for grafting rootstocks, and some can be reused in the nursery for the next growing season’s crop.

Air layering

In air layering (or marcotting), the target region is wounded and then surrounded in a moisture-retaining wrapper such as sphagnum moss, which is further surrounded in a moisture barrier such as polyethylene film. Hormone rooting powder is often applied to encourage the wounded region to grow roots. When sufficient roots have grown from the wound, the stem from the parent plant is removed and planted.

Adventitious – Appearing in an abnormal or unusual position or place, such as a root.

Plant propagation, a term gardeners use when describing everything from producing new plants, to specifically using a plant propagator to help new plants along. But what does it actually mean?

Plant propagation is the process of artificially or naturally distributing plants. This doesn’t necessarily mean you use a ‘propagator’ despite most people using the term to infer they will. There are two ways this can happen, sexual propagation and asexual propagation:

Sexual propagation is the process of an organism reproducing using another organism.

Seeds and spores can be used for reproduction (e.g. sowing the seeds). Seeds are typically produced from sexual reproduction within a species, since because genetic recombination has occurred plants grown from seed may have different characteristics to its parents. Some species produce seed that require special conditions to germinate, such as cold treatment.

Asexual propagation is the process of a single organism producing a new organism alone, that is identical to itself.

Plants have a number of mechanisms for asexual or vegetative reproduction. Some of these have been taken advantage of by horticulturists and gardeners to multiply or clone plants rapidly. People also use methods that plants do not use, such as tissue culture and grafting. Plants are produced using material from a single parent and as such there is no exchange of genetic material, therefore vegetative propagation methods almost always produce plants that are identical to the parent. Vegetative reproduction uses vegetative plants parts or roots, stems and leaves. Therefore, propagation via asexual seeds or apomixis is asexual reproduction but not vegetative propagation.

Techniques for vegetative propagation include:

• Air or ground layering
• Division
• Grafting and bud grafting, widely used in fruit tree propagation
• Micropropagation
• Stolons or runners
• Storage organs such as bulbs, corms, tubers and rhizomes
• Striking or cuttings
• Twin-scaling

We will discuss the different methods in a future blog post.

Some information courtesy of Wikipedia.