Propagation

Plant propagation is the art and science of increasing numbers of plants uti­lizing both sexual and asexual methods. It is not an exaggeration to say that the continued existence of modern civilization depends upon plant propa­gation.

Sexual plant propagation is accomplished using seeds or spores. Many crops grown this way are essential for environmental quality, food, fiber, fuel, medicines, shelter, and myriad other plant-derived substances essential for quality of human life.

Seeds may be harvested from wild plants or from those subject to care­fully controlled cross-pollination, which produces plants known as hybrids. These hybrid plants may have characteristics superior to their parents such as increased protein, better flavor, and pest resistance. Sexual plant propagation begins with seed harvesting and is separate from the creation of the cross-pollination process.

Seeds of most grains and vegetables require specific environmental con­ditions to germinate and grow. For these plants, proper seed harvest and storage to maintain viability and vigor are essential. Once a seed is sown, it can be expected to germinate in a period of time ranging from a few days to a few weeks.

Many seeds require special events or processes to occur before they can germinate. These may include cycles of warm and/or cool, moist treatments (stratification), cracking or wearing away of seed coats (scarification), smoke, intense heat from fire, or even passing through the digestive tract of an an­imal. Seeds of many perennial flowers as well as most trees and shrubs orig­inating in temperate climates require physical and/or chemical treatment to overcome dormancy.

Some natural and human-made plant hybrids will not retain their de­sirable traits if allowed to reproduce sexually, so they must be propagated by asexual means to produce clones. A common technique in asexual plant propagation is stimulating root growth on plant parts such as stems that have been cut off. This is known as cutting propagation and is the most common form of propagation used in ornamental nursery production.

An ancient yet common asexual propagation technique involves joining the top of one plant (the “scion”) with the root system of another. This is called grafting. Grafting allows combinations of desirable root characteris­tics of a plant (such as pest resistance) with desirable shoot characteristics of another (such as flavorful fruit). Often grafting is the only economical means to produce plants with those desirable characteristics. Grafting is a skill commonly employed in the production of fruit and nut-producing plants.

Another asexual plant propagation method is micropropagation, or tis­sue culture. In micropropagation, a very small piece of plant tissue is placed on an artificial growth medium under conditions similar to a hospital lab­oratory. Once sufficient tissue increase has occurred, plants are hormonally stimulated into differentiating to create a plant that can be grown outside the laboratory.

References

Bir, Richard E. Growing and Propagating Showy Native Woody Plants. Chapel Hill, NC: University of North Carolina Press, 1992.

Cullina, William. The New England Wildflower Society Guide to Growing and Propagat­ing Wildflowers of the United States and Canada. New York: Houghton Mifflin, 2000.

Hartman H., et al. Plant Propagation Principles and Practices, 6th ed. Englewood Cliffs, NJ: Prentice Hall, 1997.