Plant propagation is the fundamental process used to create new plants from a parent source. All methods of plant reproduction fall into one of two general categories: sexual propagation or asexual propagation. Understanding the distinctions between these two types allows growers to select the ideal method for achieving their specific goals, whether producing genetically varied seedlings or creating exact copies of a single desirable plant.
Sexual Propagation
Sexual propagation involves the reproduction of plants through the use of seeds, which are the result of genetic material combining from two parents. This process begins with the transfer of pollen to the female stigma, followed by the fertilization of the ovule to form a zygote. The resulting seed contains an embryo, endosperm (food source), and a protective outer seed coat.
The genetic variation present in the offspring is the defining characteristic of sexual propagation. This genetic reshuffling is beneficial for the long-term survival of a species because it helps a population adapt to changing environmental conditions or develop resistance to new diseases. For commercial growers, this method is often the most economical way to produce immense numbers of plants, such as annual vegetables or flowers, and is the only way for breeders to intentionally create new hybrids or cultivars.
Asexual Propagation
Asexual propagation, also known as vegetative propagation, is the process of creating new plants from the vegetative parts of a single parent. This method uses stems, leaves, or roots to generate new individuals that are genetically identical to the original plant.
The benefit of this method is the uniformity of the resulting plants, which perfectly preserves a specific genetic expression, such as a unique flower color or heavy fruit yield. Asexual reproduction is often preferred when a plant does not produce viable seeds, has seeds that are difficult to germinate, or for woody plants that would take years to mature from seed. Propagating a plant asexually can bypass the juvenile phase of growth, allowing the new plant to mature and flower much faster than a seedling would. This technique ensures that specific, desirable characteristics, like the traits of the Bartlett pear or Delicious apple, are maintained across generations.
Practical Methods of Asexual Propagation
Cuttings
Cuttings involve severing a piece of the parent plant and inducing it to regenerate the missing parts. A stem cutting should be taken from a healthy shoot, with the cut made just below a node, where roots are most likely to emerge. To focus the plant’s energy on root development, all flowers, buds, and the lower leaves that would be buried in the medium must be removed.
For many species, dipping the cut end into a rooting hormone (containing synthetic auxins like IBA) speeds up root formation. The cutting is then inserted into a sterile, porous, and well-draining medium, such as a mix of peat moss and perlite or vermiculite. Providing a warm, humid environment, often by covering the pot with a plastic bag, is necessary to minimize water loss until the new roots can support the cutting. Leaf cuttings (e.g., African violets) must form both new roots and new shoots from the leaf tissue, while root cuttings generate a new shoot system from root pieces.
Layering
Layering is a method where a stem is encouraged to root while it is still attached to the parent plant. This process avoids the water stress and carbohydrate shortage that cuttings often experience after being severed.
Simple layering involves bending a flexible branch to the ground, wounding a section of the stem, and burying it in the soil. The accumulation of carbohydrates above the wound encourages root formation, after which the rooted stem is cut from the parent plant. Air layering is used for plants with stiff stems (e.g., citrus) and requires removing a strip of bark (girdling). Moist sphagnum moss is packed around the exposed area and wrapped in plastic film to maintain humidity.
Division
Division is a method for propagating clump-forming plants, such as herbaceous perennials, ornamental grasses, and bulbs. This technique involves physically separating a large plant clump into smaller, viable pieces, each with its own root system and shoot buds.
A plant often signals its need for division when the center of the clump begins to die out or when flowering becomes sparse and less vigorous. The entire clump is dug up, and excess soil is shaken off to expose the root mass. Separation can often be achieved by pulling the root sections apart by hand, but tougher root balls may require a sharp knife or two garden forks to pry the clump apart. Each resulting division must contain a healthy portion of roots and at least two or three shoots to ensure successful establishment when replanted.