Propagation of house plants

Plants can be propagated in two basic ways: sexual reproduction (by seeds or spores) or vegetative reproduction (from cuttings, division, separating plantlets and so on).

Sowing seeds

The size of seeds is the first consideration. Generally speaking, small seeds are sown on the surface, whereas larger seeds are covered with a layer of compost about twice as thick as they are. Press the compost down lightly. Cover the seed tray with a sheet of glass to prevent it drying out. The glass should be turned over at least once a day so that the drops of water which condense on the under-surface do not fall back on the seeds or young seedlings.

A good seed compost can be prepared by mixing sand and peat or well-rotted leaf mould plus some perlite to make it lighter.

Seeds are generally sown in the spring. This allows the young plants to make good growth before autumn and so they are better able to survive the harsh conditions of winter. However, seeds that rapidly lose their germinating power must be sown as soon as they are ripe.

Vegetative propagation

Vegetative propagation is a commoner method for increasing house plants. New plants can be obtained more rapidly and often more simply than from seed. There are several methods, each making use of the characteristic properties of the particular plants. These include plant and root division, taking cuttings from various parts of the plant, and detaching young plantlets or bulbs from the parent plant.

Older plants are often divided when they are repotted. Divide the plants into two or more clumps by gently pulling them apart. If this is not possible, cut them into clumps with a sharp knife. Pot up the separated clumps into suitably sized pots. The ‘new’ plants continue growth immediately because they have both roots and leaves and therefore do not have to expend energy on forming new ones. This method is used to propagate Clivia, Sansevieria and Aspidistra. Many species of orchids are multiplied by dividing clumps of tubers.

Another very simple method of vegetative propagation is by detaching young plant-lets from the parent. Some plants, such as some bromeliads, Ledebouria and Haeman-thus albiflos, produce numerous offsets. In others, such as Bryophyllum tubiflorum, whole new baby plants are formed on the margins of the leaves. Saxifraga sarmentosa and Chlorophytum comosum produce new plants on long aerial runners, stolons. Small bulblets are often formed on old bulbs and these can be detached. Both young plant-lets and bulblets should be potted up immediately into appropriately sized pots and left to root there.

Taking cuttings offers the widest scope for vegetative propagation. Various parts of the plant body, if they are correctly cut off and cultivated, are capable of rooting and growing into new plants. Cuttings of some species will root far more readily than others and some techniques are not suitable for particular plants. For example, cuttings taken from Pelargonium, Tradescantia and Fuchsia root readily and rapidly under normal conditions of growth, whereas those of Ficus, Callistemon and Medinil-la root with difficulty and require special handling. Many species, especially grasses and ferns, cannot be propagated by cuttings at all. Success with taking cuttings depends on the ripeness of the plant tissues and on the amount of natural growth hormone present. This is why it is best to take cuttings in spring and early summer.

External factors, such as the rooting medium, micro-climate and growth stimulators, are also decisive. The rooting medium must be loose and rather on the light side. Sometimes only sand is used. It must also be sufficiently moist and warm. Humidity and temperature are crucial. The latter should be about 25 °C (77 °F). The higher the temperature, the greater the need to provide moisture.

A propagator will provide the optimum micro-climate. It may be heated or un-heated. A heated propagator consists of a glass or ceramic container with an electric heating element underneath. Alternatively, heat may be provided by placing the container on a radiator. The container is covered with a transparent glass or plastic lid. A plastic bag can make a good do-it-yourself substitute.

Rooting may be stimulated by dipping the cut surface in a proprietary hormone rooting powder. Natural growth hormones present in the cuttings may also be activated by well-considered bruising of the tissues. This can be done by severing the main vascular bundles in the leaf or by making a cut in the stem.

The different kinds of cuttings, depending on the part of the plant from which they are taken, are stem, leaf, root and rhizome cuttings.

Stem cuttings may be herbaceous (soft-stem cuttings) or woody (hard-stem cuttings). They are either taken from the tip of the stem, together with several leaves and buds, or else from a lateral shoot. Usually a long slanting cut is made with a sharp knife. In a few species, such as fuchsias and chrysanthemums, the cuttings are broken off or cut with blunt scissors. As a rule, the cuttings should be put in a prepared rooting medium in a pot and a propagator as soon as they have been taken. Only in a few cases, including pelargoniums and some succulents and spurges, should the cut surface be left to dry before insertion in the rooting medium. The cuttings of many species, particularly Tradescantia, Philodendron, Monstera, sparmannia and oleander, root better in water than in a rooting medium. Put the cutting in a container filled with water and pack cotton wool in the neck to slow down evaporation. Change the water after a week. The remaining part of the cut-off stem of the parent plant often puts out new shoots. Hard cutting back rejuvenates Dieffenbachia, Aglaonema, Ficus and many other plants.

Woody-stemmed plants that are difficult to root, especially Ficus, can be propagated by air-layering. To do this, make an upward cut at a sharp angle beneath a leaf stalk, at the point on the stem where you want new roots to form. Do not cut right through the stem. Carefully insert a matchstick so the cut will not close and brush with hormone rooting powder. Wrap damp moss round the cut and secure with wire. Better still, hold the moss in place with a tube of polythene secured with adhesive tape. This will help to keep the moss moist. Maintain a temperature of about 25 °C (77 °F). Depending on the species of plant, roots will appear at the site of the cut within about three weeks. Cut the stem just below the roots and pot it up, together with the moss packing. The best time for this method of propagation is in June and July.

Leaf cuttings are prepared in one of two ways, depending on the species of plant. The simplest method is to cut off a leaf with a piece of stalk and insert it in a moist rooting medium or in water. Cover the pot with a polythene bag secured with a rubber band. New roots and shoots appear at the base of the stalk. This method is used to propagate Saintpaulia, Cyperus and Peperomia, for example. The leaves of some succulents, such as Crassula, Pachyphytum, Adromischus and Sedum, are broken off and laid on the surface of the rooting medium. Roots and new plantlets grow from the break.

The second method of propagation by leaf cuttings is to sever the main vascular bundles in the leaves or to cut up large leaves into several sections. Insert the sections in the rooting medium with Sansevieria, or merely lay them on the surface with Begonia. Cover with a sheet of glass or a plastic bag.

Root cuttings of such plants as Cordyline and the cuttings from rhizomes of ferns, such as Phlebodium and Cyrtomium, should be left to dry and then inserted in the rooting medium. Each root cutting and section of rhizome must have an adventitious bud which will develop into a new plant.

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