Propagation from Stem Cuttings
For the past several weeks, some Master Gardeners of Cochise County have been attending an advanced training course on the techniques of plant propagation where they have been learning the secrets of making new plants from old ones. The most recent class, propagating plants from stem cuttings, was presented by Elizabeth Davison who teaches the subject at The University of Arizona, Tucson. Her lecture inspired me to hit the cyber surf and see what the Web has to say about the subject.
Most of us have had some experience rooting herbaceous houseplants from stem cuttings but many people don't realize that you can propagate all types of plants from cuttings, including trees and shrubs. One of the advantages of this method of propagation is that you know that the new plant will look just like the "parent." You can't have that assurance with seeds. Although the "mother" may have all the characteristics you want, you generally have no idea what the "father" was like.
According to the Arizona Master Gardener Manual (http://ag. arizona.edu/pubs/garden/mg/), "a cutting is a vegetative plant part which is severed from the parent plant in order to regenerate itself, thereby forming a whole new plant." Cuttings may be taken from roots, leaves, or stems. As the name suggests, stem cuttings are taken from a piece of a growing limb or shoot. The basic techniques for propagating a plant from a stem cutting are fairly simple. Cut a piece of stem from a plant, stick it into a rooting medium such as coarse sand, keep the medium moist until the new roots appear, and transplant the rooted plant.
Understanding the underlying science will help improve your success rate.
? There are only certain places, called meristematic areas, where plants can generate new roots. Meristematic areas occur at the tips of shoots, buds and roots. In order to successfully root a stem cutting, you have to wound a plant near a bud and make sure that the wounded area is in close contact with the rooting medium.
? Rooting occurs in response to a hormone called auxin which is produced naturally by the plant. In order to insure that there is enough auxin to grow new roots started, most horticulturists dip the cut tip into a product containing either indolebutyric acid (IBA) or naphthalene acetic acid (NAA). These products are generally sold in powder or liquid forms. Trade names include "Rootone," "Dip 'N Grow," "Hormonex," and others.
Since roots are the plant organs that are responsible for providing water to plants and new cuttings have no roots, it is necessary to take extra care that the cutting does not dehydrate before the new roots develop. This is done by surrounding the leaves of the cuttings with highly humid air to cut down on the loss of water by evaporation from the leaves and removing all but a few leaves from the cutting. Moisture can be trapped around the leaves by enclosing the cutting in a transparent or translucent covering such as plastic wrap or a plastic container. Replenish the moisture inside the covering by misting with a spray bottle. Remember, however, to remove the covering briefly at least once a day to allow fresh air to enter.
? Before roots develop the cuttings also have no way of getting nutrients. This means that they must subsist off the sugars that were stored in their tissues when they were cut. To generate the maximum energy for root formation remove all flowers and flower buds from the cutting that would divert the limited energy supply to the formation of fruit and seeds.
Other considerations.
* In order to cut down on the risk of transmitting a disease to your cutting, sterilize your cutting blade with rubbing alcohol or a dilute solution of bleach before making a cutting.
* Do not use ordinary soil as a rooting medium. Instead use sand, vermiculite, perlite, or peat moss which do not contain potentially pathogenic organisms.
* Keep the temperatures of the rooting medium and air around the plant fairly constant - 55-65?F air temperature and 65-75?F for rooting medium temperature.
* Keep the rooting medium constantly moist but do not submerge the tip of the cutting in water. Submerging the tip deprives the cutting of oxygen.
* Do not place the cuttings directly in the sunlight. Too much sun light will cause the temperatures to rise to lethal levels inside the covering.
Some useful Web sites for propagation include:
o This site from the Cooperative Extension of the University of Florida provides a general introduction to the subject of propagation from cuttings (http://edis.ifas.ufl.edu/scripts/ htmlgen.exe?body&DOCUMENT_MG275)
o This is a commercial site sponsored by a company that makes a rooting hormone. In addition to product information, however, it also includes an extensive collection of articles on propagation techniques (http://www.rootinghormones.com/SITEMAP.HTM) This site from the University of California at Davis provides a database showing propagation data for an extensive list of plants, including the type of cutting, time of year, rooting medium used, rooting hormone, temperatures used, percent of success achieved, time to root, and other data (http://telework.ucdavis.edu/root/pchome.htm) Until next month, happy surfing!