What is Propagation?

Plant propagation is the process of creating new plants from various sources such as seeds, cuttings, bulbs, and other plant parts. It also encompasses the natural or artificial dispersal of plants.

Sexual Propagation

Sexual propagation involves using seeds and spores for reproduction, typically achieved through sowing. Seeds are the result of sexual reproduction within a species, and since genetic recombination occurs, plants grown from seeds can exhibit characteristics different from their parents. Some species produce seeds that require special conditions for germination, such as cold treatment. For instance, many Australian plants, as well as those from southern Africa and the American west, need smoke or fire to germinate. Certain plants, including many trees, do not produce seeds until they reach maturity, which may take several years. Additionally, obtaining seeds can be challenging, and some plants do not produce seeds at all.

Asexual Propagation

Asexual or vegetative propagation allows plants to reproduce without sexual reproduction. This method utilises parts of the plant, such as roots, stems, and leaves, to produce new plants that are genetically identical to the parent. In contrast to sexual reproduction, which involves genetic exchange, asexual propagation does not involve genetic recombination. Plants can also reproduce asexually through apomixis, where seeds are produced without fertilisation, containing only the genetic material of the parent plant.

Different Types of Propagation

Layering

Layering is a technique where a portion of an aerial stem grows roots while still attached to the parent plant, eventually detaching to become an independent plant. This method is common in natural environments and is also used by horticulturists to propagate desirable plants. In natural layering, a branch touching the ground will produce adventitious roots. In horticulture, the process often involves wounding the target region of the stem, applying rooting compounds, and then burying the stem in soil. This allows the propagated portion to continue receiving water and nutrients from the parent plant until roots are formed. Layering can take several weeks to a year.

Ground Layering

Ground layering is a common technique for propagating clonal apple rootstocks, where the stem is laid nearly horizontally in the ground. Side buds grow upward, and the stem is buried up to the tip. By the end of the growing season, the side branches will have rooted and can be separated for use in grafting or for future crops.

Air Layering

In air layering, the target region of a stem is wounded and surrounded with a moisture-retaining material like sphagnum moss, which is then covered with a moisture barrier such as polyethylene film. Rooting hormone is often applied to encourage root development. Once sufficient roots have grown, the stem is cut from the parent plant and planted. The process typically takes about three months.

Division

Division is a method of asexual plant propagation where a plant, usually an herbaceous perennial, is separated into two or more parts, each with intact roots and crown. This ancient technique is used for bulbs like garlic and saffron and is mainly practised by gardeners and small nurseries, with larger commercial propagation increasingly relying on tissue culture.

Grafting

Grafting involves inserting tissues from one plant into those of another so that the vascular tissues join together, a process known as inosculation. This technique is widely used in horticulture and agriculture. Typically, one plant provides the roots (the stock or rootstock) while another provides the stems, leaves, flowers, or fruits (the scion). The scion contains the desired genes for future plants. In stem grafting, a shoot from a desired plant is grafted onto a different stock. In bud grafting, a dormant bud is grafted onto a stock stem and encouraged to grow after the stock’s stem is pruned above the graft.

Micropropagation

Micropropagation is a modern method of rapidly multiplying plant material using tissue culture techniques. This approach is used to produce large numbers of plants from a single stock plant, particularly those that are genetically modified or do not produce seeds. Frederick Campion Steward pioneered this technique in the late 1950s and early 1960s. The process begins with selecting and sterilising plant material, which is then placed on a growth medium to encourage tissue growth. The multiplication stage involves increasing the number of plantlets through repeated cycles of tissue culture. Pre-transplanting involves acclimatising plantlets to soil conditions, transitioning from a high-humidity, controlled environment to a more natural one. Finally, plantlets are transferred from culture to soil or potting compost for continued growth.

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