Own Root Only? Not so fast!
John H. Barbour, President, Bold Spring Nursery
In recent decades traditional seedling propagation of ornamental trees has given way increasingly to the use of cultivars through clonal propagation. Many seedling-grown trees display significant genetic variation and the resultant lack of uniformity in a population can be, for some, troublesome in mass planting in a modern landscape. The desire for uniformity in the commercial landscape and the selection of superior varieties has contributed to the demand for cultivars. Through propagation techniques such as grafting, budding, rooted cuttings, and tissue culture, the inherent qualities of a single specimen can be genetically replicated and displayed predictably in the landscape.
However, clonal propagation in and of itself must not be considered the end-all solution for tree production. When thinking of the long term health of the urban forest, here seed-propagated trees offer advantages. Biodiversity is an important aspect in controlling widespread damage due to constantly evolving pest problems in any given ecosystem. The use of seedling-grown trees insures the broadest gene pool to offer resistance to insects and pathogens. For this reason alone, seedling production should and will remain an important segment of our industry.
Still, it is that very diversity that provides the opportunity for selecting cultivars which seem to stand out from the rest. The need for improved selections varies between species. Many oaks offer very good uniformity when grown from seed and may be effectively substituted for clonal trees in many situations. Yet Acer rubrum, our native red maple, from seed, exhibits great genetic elasticity and provides a dramatic array of characteristics among seedlings, but, in fact, many representatives are not the most attractive landscape trees. Superior selections of Acer rubrum have been made and, when the clones are used in mass, they offer a powerful visual effect of repetition of color and form in the landscape. The success of outstanding red maple cultivars such as October Glory® has led to a wave of cultivar development within a number of species. It is to be hoped that new cultivars are chosen carefully to offer characteristics superior to their species. The creation of a clone should be a means to that end and not, of itself, the end goal.
At Bold Spring Nursery we grow trees from a variety of propagation techniques: rooted cuttings, seedlings, tissue culture, budding, and grafting. Though the majority of our trees are produced from rooted cuttings, we are constantly evaluating the pros and cons of various techniques in order to optimize the quality of each tree in our inventory. There are no absolute rules.
Depending on the tree, the results are varied. Some species, such as Acer palmatum (Japanese maple) cultivars, have been grafted successfully for hundreds of years. We have produced them from grafts and also from rooted cuttings and, in most cases, grafts have proven to be more vigorous. Several other species, Carpinus betulus (European hornbeam) and Zelkova serrata (Japanese Zelkova) for example, have shown similar results, with budded plants out-performing rooted cuttings. A few species, such as Nyssa sylvatica (black gum), rarely produce good root systems from rooted cuttings but perform very well when budded. Occasionally, as with red oak types and our native red maple, graft incompatibility problems preclude that method and rooted cuttings become the technique of choice. Even in those cases there are many exceptions and, sometimes, a variety is so difficult to root from cuttings that the root system is insufficient to provide long-term stability. In such cases rooted cutting propagation does not make sense; the benefits offered by that particular cultivar are outweighed by the need for the best possible root system.
The advantages of grafting and budding were, perhaps, illustrated most inspirationally by the late Dr Frank Santamour, Harvard PhD, and renowned research geneticist at the National Arboretum. Dr Santamour was recognized as the worlds leading authority on the genetics, breeding, and development of superior landscape trees. He once described the three methods for making a better tree for the world. The first method is “to find” a better tree. This method has been exemplified often in the nursery trade with such introductions as Red Sunset® maple and Athena® Classic elm resulting from the fortunate observation of a discerning plantsman. The second method is “to breed” a better tree. Although landscape trees have not been bred nearly to the extent of shrubs and herbaceous plants, there have been many outstanding breeding success stories, none more brilliant than the series of tree-form crapemyrtles bred by the late great Dr. Don Egolf during his career at the National Arboretum. The products of his work, including 'Natchez', 'Muskogee', and many others, extended the use of crapemyrtles by improving their cold hardiness, disease resistance, and ultimate stature. The third method is “to build” a better tree. This method has been utilized extensively by the fruit industry for centuries. Long ago fruit growers recognized that the best top of a plant, in some cases, might not produce the best root system. They learned to select root systems for different purposes: dwarfing effect on apples and root-rot resistance on grapes, for example. Through the techniques of grafting and budding the growers refined their ability to combine the best rootstock with the best top. Because of the economies of scale in the fruit industry, they have far surpassed the ornamental industry in this regard and they have enjoyed the long-lasting benefits on millions of trees for hundreds of years. The landscape tree industry is only beginning to explore the potential of this next frontier.
The choice of a particular method of propagation is not simple. We are fortunate to have many methods at our disposal. At Bold Spring Nursery we will continue to optimize all viable methods of propagation to offer the best possible mix of trees to the landscape trade. Each tree has unique propagation needs and we are on a quest to know each tree and grow each according to its unique needs.