Vegetative Propagation
By Frances Batcheller
May - June 1964, Gesneriad Saintpaulia News, pages 16-17
The Gesneriad family has a remarkable capacity for vegetative reproduction. Only two other plant families — Crassulaceae and Begonieae — have similar abilities. This characteristic is a large factor in their popularity, with the home grower who likes to share favorite plants, with the commercial grower who needs rapid multiplication and with the hybridizer who wants to perpetuate sterile hybrids. Gesneriads can be propagated from single leaves, auxilliary shoots, offsets, stolons, or tip cuttings as well as by the normal methods used by the plant for propagation with scaly rhizomes, propagules or tubers. With all these methods to work from, successful propagation can be achieved by any one willing to devote time and effort to the project.
The single leaf method is extensively used with Saintpaulia and Sinningia. The leaf may be rooted in several ways. It will generally root in water. Wax paper or metal foil should be placed over the top of the container and held down with an elastic. Holes are punched to allow the stem to reach the water. The water level must be kept high enough to reach the end of the stem during the rooting process. The main advantage of this method is visibility and being able to check on progress.
It also uses materials readily available to anyone. The main disadvantage is that the roots which develop are apt to be weak and clump together when the leaf is transferred to a pot.
Another method is to use a shallow container filled with a porous rooting medium such as moss, vermiculite or perlite. The stems are inserted in this medium which is kept damp. This method can be used for short-stemmed or stemless leaves. The roots which form are generally much stronger than by the water method and are far easier to transplant. The rooting medium should be kept loose and well aerated.
A third method is to put about two inches of damp vermiculite in the bottom of a plastic bag and insert the stems in this medium. A coat hanger will hold several bags fastened with clip clothespins. This method saves space and requires little attention. If the vermiculite is too damp, there may be some rotting of the leaves. It should be checked carefully for the first week. Leave the top of the bag open if it seems too damp.
A terrarium or large plastic box can also be used to start leaves or cuttings. An aquarium covered with a sheet of plastic can be very useful for this purpose. Some air circulation must be provided. If a large quantity of water condenses on the top and sides of such a container, the rooting medium is too damp and the cover should be left off for a time to enable it to dry out somewhat.
To increase the yield from Sinningia leaves, the stem may be split and usually a tuber will form on each half. Also the leaf may be cut in sections, taking wedge-shaped pieces from the area surrounding the main or large lateral veins. Sometimes these leaf cuttings will form only fibrous roots. After potting up new growth may appear or the mother leaf may gradually die back. In this case, a small tuber is usually found in the soil. After a resting period, this will start in with new growth.
Any large leaf, such as Sinningia, Rechsteieria or Streptocarpus is difficult to root, and results are frequently better if the leaf is reduced in size by a half or more. Generally this is done in a V cut, parallel to the lateral veins. Any cutting should be done on a flat surface with a razor blade, as this bruises the tissue far less than a knife or scissors. With these methods involving cutting, it is a good idea to practice on easily available varieties, rather than trying it for the first time on a particularly choice variety.
Another method that can be used for large flat leaves is the one frequently used for Begonias. This involves making cuts across the large veins on the underside of the leaf. The leaf is then pinned down, right side up, on damp rooting medium. New plantlets will appear around the cut area.
Offsets, or suckers, frequently form around the base of rosette-type Gesneriads, such as Saintpaulia, Petrocosmea and Boea. These may be cut off and rooted in the same manner as individual leaves. Streptocarpus plants have a tendency to progress in a straight line, rather than in a circle, and a plant can be divided by cutting between the plantlets and potting each one up separately. Extra shoots that form on Sinningias or X Gloxineras can also be cut off and rooted, as these plants are generally preferred in a single crown, as is Saintpaulia.
Stolons, long shoots produced from the leaf axils of Episcias, may be cut off and rooted, or rooted while still attached to the mother plant, as the analogous strawberry runner.
Tip cuttings, the terminal end of a stem with several pairs of leaves, are the traditional way to multiply most house plants. They will root easily in either water or rooting medium. Old woody growth is more difficult than younger growth, but very new growth is generally unsatisfactory. Any of the trailing or bushy Gesneriads do well by this method, especially Columneas and Aeschynanthus. Tip cuttings or Kohlerias frequently make better plants than those started from rhizomes.
Scaly rhizomes are a natural method of vegetative propagation for some Gesneriads. These storage roots generally form toward the end of the growing season. They resemble small pine cones, although some rhizomes, such as Kohleria, may grow to considerable length and wind around inside the pot. The rhizomes are harvested when the top of the plant dies back after flowering. This is easier if the soil is allowed to dry out so the rhizomes break quite easily, but pieces or even single scales can generate new plants. In Achimenes especially, one plant grown from a rhizome will produce fifteen to twenty new rhizomes by the end of the summer. The rhizomes should be planted horizontally and covered by not more than an inch of soil.
Scaly rhizomes may also appear in the leaf axils, usually at the end of the growing season or in protest of poor cultural conditions. These are termed propagules and can be separated off and planted. Titanotrichum has a curious whiplike growth covered with small scales which can be rubbed off and planted like seed.
Sinningias, X Gloxineras and Rechsteinerias grow from tubers. These generally do not multiply, only increase in diameter with age, therefore single leaves or shoots are used to multiply these plants. The tubers should be planted just below the surface of the soil and the pot should be shallow but large enough in diameter to allow plenty of growth room.
The ends of cuttings can be dusted with a rooting powder, but this is not particularly necessary as Gesneriads root so easily. However, a fungicide is frequently beneficial in preventing rot. If rotting does occur on a cutting, sometimes it can be saved by cutting out the bad section and dusting the cut with sulphur. Rotting generally indicates too damp conditions and poor air circulation.
Labeling cuttings or leaves is always a problem. Adhesive or marking tape can be used on leaves, but it does not always stay on in a damp atmosphere. The stem can be put through a hole in a slip of paper marked with heavy pencil. With luck this will remain legible until the leaf can be potted up. If plastic bags contain only one item, the slip can be put on the outside. If the material is rooted in a flat, each piece can have a small plastic label, which can be transferred to the pot at the proper time.
The important points to consider in propagation are to keep the material in an atmosphere of adequate humidity to keep the leaves from drying out and to keep the rooting end of the cutting in a damp medium which permits air circulation. Adequate light is necessary to keep the chlorophyll in working order to feed new growth. Strong sunlight and overheating will be damaging, however. The temperature should be kept between 7O~75 degrees if possible. Bottom heat will usually speed rooting, if it can be provided. Trial and error will demonstrate the best results in your particular conditions. Some are more successful with one method than another.
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