Propagation is the term used to describe the process of plant reproduction. There are two categories of propagation, i.e. seminal and vegetative. Seminal propagation results from sowing seeds. Plants grown from seed are entirely unique and may differ from each other and from the parent plant. Vegetative propagation embraces all other techniques of reproduction such as cutting, grafting and layering and plants propagated in this manner are identical to their parents i.e. they are clones.
The terms softwood, semi-ripe and hardwood are to plant life the equivalent to the stages of infant, teenager and adult life in humans.
Softwood – is taken very early in the growing season, before there is any sign of hardening of the new shoots. They are green, both at the tip and base.
Semi-ripe – is taken at the end of the growing season when the tip of the stem is soft and green, but the base is hardening, going brown and starting to become woody.
Hardwood – is taken in the winter when the stem has become hardened and woody throughout its length.
Other terms used in cutting jargon are heel, stem and tip. These refer to the part of the stem that is being used for the cutting.
Heel cutting – the stem is torn off in a way that retains a portion of the parent branch – a heel – at its base. Heel cuttings are most often made from softwood or semi-ripe wood. They are normally about 3 to 15 cm long.
Stem cuttings – most often used for hardwood cuttings. They normally include 20 to 30 cm of the stem to provide a reservoir of nutrients so that the cutting can survive through the winter until growth begins in spring.
Tip cuttings – short portions 3 to 15cm long taken from the tips of the stems. These parts are used for softwood and semi-ripe cuttings.
The reason for the different types of cuttings is that some species will propagate more readily from a stem cutting than a root cutting. There are, however, many plants that will reproduce from more than one type of cutting.
Cuttings are encouraged to grow roots and to this end they require moisture, light and a clean, free draining soil. A dusting hormone in the form of rooting powder may be used to help cuttings take root. It is advisable to strip most of the leaves from the cutting in order to reduce the amount of moisture lost through transpiration, while the remaining leaves will add to the food reserves through photosynthesis.
This is the quickest way to increase perennials that have a spreading rootstock and produce new shoots annually from the crown. Division is best carried out when the plant is dormant. Lift the parent plants and shake off excess soil from the roots. Separate the plants into sections using a garden fork, a spade or a sharp knife. Ensure that each plant has a good root system. Discard old or damaged pieces and replant the segments at the original depth of soil. Examples of this type of division include Agapanthus, Clivia, Iris, and Shasta Daisy.
Most seed is best sown as soon as ripe. If necessary, soak fruits in water first, then extract seeds by rubbing the flesh and leave to dry. Hard-coated seeds may need soaking or scarification before germination. Soak in recently boiled water from between 10 minutes to 72 hours, depending on the species. Viable seeds will swell and should be sown immediately in situ or in a tray or seedbed. Soil should be kept moist. Lightly cover the seeds with compost or soil. As a general rule, cover seeds with about their own depth of soil. Mix fine seeds with a little dry river sand, trickle them over the compost and do not cover. Ensure that the seeds are kept moist.
Stored in a dry place most seeds remain good for 2 to 3 years but germination rates gradually decline.
Layering, suckers and grafting
Layering is a simple method for increasing plants with stems that will produce roots if wounded. The stem is pegged into the ground and left to form roots, while still attached to the parent plant.
Suckering plants, such a Tecomaria, Wisteria and Plumbago, naturally produce suckers that may be detached and inserted as ready-rooted plants.
Grafting involves taking the stem of one plant and uniting it with the rootstock of a closely related plant. Roses and fruit trees are propagated in this way. Grafting is best left to the specialists.