>> Lab Introduction and Overview
Despite the usefulness of the World Wide Web as an instructional tool for this course, hands on learning is an irreplaceable part of the learning experience. This is true, I believe, not only for learning the art and science of grafting in particular, but also the field of horticulture in general. Hence, the goal of this section of the course is to provide students with a hands-on opportunity to apply the principles of grafting learned elsewhere in this course to the practice of three different grafting and budding methods. These include include T-budding, Chip Budding, and Top Wedge Grafting. There are, of course, many other methods worth learning, but these three were chosen because they are relatively easy to learn by beginners, and/or because they are commercially important. Once you have become familiar with these methods, you should have the ability and confidence to learn many others on your own.
A. Why hibiscus? Hibiscus as a model system for learning how to graft.
1. Why not other species that are more commonly grafted in this part of the world?
For many years, the author has taught hands on grafting skills using several different temperate woody plant species, including apple, spruce and juniper. Using these temperate species to teach grafting was seasonally limited by their natural cycles of active growth and dormancy. For example, T-budding of apple, which requires that the bark be slipping, could not be taught after late summer. Furthermore, success in grafting these relatively difficult-to-graft species required a level of skill which many students do not develop without considerable practice, resulting in initial failure, frustration and a less-than-positive learning experience.
2. Hibiscus has advantages over other species as a system for learning grafting.
- It grows actively year round in a suitable greenhouse. Hence there is no problem of seasonal dormancy. Grafting skills can be taught at any time of year.
- It is relatively easy to graft so students tend to have a more positive learning experience.
- It makes a nice "souvenir" of the class. Several different colored flowers on the same stock can be a big hit at home.
B. About Hibiscus. The biology and horticulture of this species.
1. Hibiscus and its relatives
The tropical or Chinese hibiscus, Hibiscus rosa-sinensis, is a tender (not winter hardy) woody perennial which originated in the vicinity of the Indian Ocean. Hibiscus is in the mallow (Malvaceae) family which includes the genus Hibiscus and several other genera. For example, Okra, cotton, and hollyhock are members of the Malvaceae family .
- This U.S. Forest Servcie factsheet describes the related ornamental hibiscus species, H. syriacus (Rose-of-Sharon) , which is hardy, and occasionally found in NY landscapes.
The genus Hibiscus is characterized by single flowers with typically have five petals (except "doubles") and a 'staminal' tube consisting of 60-70 stamens appressed around the style which bears five stigma pads at its apex. Flowers also have a five cell ovary, five teeth on the calyx, and five to ten bracts. Because of its intolerance of frost, unprotected culture of tropical hibiscus (outdoors) is limited to Zones 9-10, which, in the US, includes much of Florida, the southern most extremes of Louisiana and Texas, southwestern Arizona, and the Central Valley and much of southern California, and Hawaii. In fact, hibiscus is the state flower of Hawaii, and the national flower of Malaysia. The unselected species, Hibiscus rosa-sinensis, has a bright red flower, but breeders have hybridized this species with several other hibiscus species and selected a wide range of flower colors including reds, pinks, oranges and yellows, and even blue. Recently, many hybrid polyploid selections have been made, creating plants with multicolor and/or double blooms.
- Color photos of the cultivars you will be using for these lab exercises.
- Color pictures of some of these varieties are displayed on the Web site of the American Hibiscus Society. If you are interested in pursuing hibiscus culture further, this site is a good source of information.
- Lists & Lists...Hibiscus Species, Varieties, and Cultivars & Trade is a Web site that lists modern hibiscus cultivars in various categories including the "garden" varieties which are typically rooted from cuttings and the hybrids which are typically grafted.
2. Commercial propagation of Hibiscus (or the relevance of this lab to the "real" world).
Because hibiscus is quite genetically heterozygous it does not come true-to-type from seed, so selected varieties and interspecific hybrids must be clonally propagated. The unselected species H. rosa-senensis and the so called "garden varieties" are relatively easy-to-root and subsequently perform well when propagated from cuttings. This is not the case with many of the large flowered interspecific hybrids. This is one reason that many commercially available hybrid hibiscus varieties are grafted, but the other reason is that even if they are successfully rooted and grown from cuttings, they do not grow as vigorously on their own roots as they do when grafted to more vigorous varieties of H. rosa-sinensis. Marcottage (air layering) and tissue culture are alternative, but not common, methods of vegetative propagation of hibiscus.
- Ganmor Gardens, in Australia, has an excellent tutorial on grafting hibiscus, which is similar to the hibiscus grafting you will be doing in these HWWG lab exercises.
C. Materials you will use in the Hibiscus Lab Exercises
1. Grafting / Budding Knife
2. Wrapping materials
D. Sharpening your grafting knife
There several different methods for sharpening a grafting or budding knife. These include the use of a sharpening stone (wet or oil) and leather strop, emery cloth, or a diamond sharpener. Here is a great link about knife sharpening: Ron Hock's Sharpening Notes.
The knives provided for your lab are very sharp. Please exercise caution.
F. If you are ready, proceed directly to the Laboratory Exercises: