When the roots are developed enough to support the end of the branch, usually in 2 years, the rooted-branch is cut from the parent plant and transplanted.
Grafting: Grafting was the standard propagation technique prior to the s, and is still popular in Europe where acidic soil is not common and plants that are hard to grow can be grafted onto rootstocks of plants that are easy to grow like R.
The big advantage of grafting is the use of disease resistant, soil tolerant rootstocks. Also, some hybrids don't produce good root systems, so if the plants are grafted onto a good rootstock, this is no longer a problem. There are two basic techniques of grafting, one involves grafting onto rooted rootstocks and the second involves grafting and rooting the rootstock at the same time. Then the scion is grafted to the rootstock and secured with an elastic band. See the referenced articles below for detailed instructions.
The cuttings for the rootstock and the scion are taken at the same time. The scion is side grafted to the rootstock cutting and secured with raw cotton string which rots naturally. The top is left on both cuttings. The rootstock is rooted immediately after the graft is secured.
After the rootstock has rooted, its top is removed immediately above the graft. It doesn't matter if the scion forms roots but the rootstock must not form shoots. Any such shoots are removed. Tissue Culture: Tissue culture or micro propagation is a popular method of producing large numbers of rhododendrons for commercial production. Over simplified, it involves taking a small vegetative shoot section from the parent plant and putting it into a test tube.
Through the use of agars and auxins, absolute sanitation, proper temperature and lights, the vegetative shoot is induced to grow into multiple "seedling-like" growths with no roots.
This tiny juvenile vegetative shoot is then rooted. Needless to say, this method is not for the general home gardener, though some "kitchen tissue culture" is being done see reference article. American Rhododendron Society P. Plant Culture and Care. Landscape Use. Plant Selection. What To Plant Where. Weather Protection.
Remove the bottom leaves at least 1 inch up from the bottom of the stem. Use a sharp knife to make a small cut in the bark on each side of the stem at the bottom of the stem. Dip the bottom of the stem where the cuts were made in a rooting hormone. Any rooting agent from a nursery will work as long as it states that it can be used to promote root growth on semi-hardwood plants.
Place the stem in the soil mixture 1 to 2 inches deep. Lightly pack the medium around the stem to hold it up. Water well. Place the two dowels in the medium, one on each side of the stem, but at the edge of the container.
Place a plastic bag over the container and the dowels. This will make a greenhouse for rooting the plant stem. This provides the essential constant conditions and allows the gardener to take a holiday once in a while. The frame is covered with Netlon mesh on sunny days and with sacking in cold weather to retain the heat.
A great many small and medium-sized species have been rooted by this method, including: R. The height of the case has been increased by a light wooden framework 12 inches high, surrounded by polythene, in order to insert a mist jet.
The mist supply can be worked by hand according to the weather or, if it has to be left unattended for a week or two, by a time clock which gives a few seconds of mist every hour. At first a layer of peat was put over the heating wires, but this tended to encourage moss, liverwort and even ferns to appear; it has now been replaced by sharp sand on which pans of cuttings are placed and which has proved entirely satisfactory.
Species raised in this frame include: R. It may be of interest to know that all the equipment described above is obtainable from horticultural suppliers. Compost The next point to be decided is the material in which the cuttings are to be rooted. Many materials have been recommended, such as peat, sharp sand, pumice, vermiculite in various combinations: e.
Whatever is chosen should be adopted as standard. It is a great mistake to chop and change, for then nothing can be learned from failures, If the variables are kept as few as possible, the difference in behaviour of various species may be understood. The mixture adopted here is 1 part peat to 1 part sharp sand.
This is varied slightly as required. A softer type of growth might like a little more peat, a harder one a little more sand, but this will be a matter of experience and it is better not to be in a hurry to make changes. Pots The modern plastic pots save a lot of time but are more difficult to manage water-wise than clays. More drainage is required and they do not need as much watering since there is no evaporation through the pot. On the other hand, for long-term use the clay pots, in the writer's experience, have the advantage that if they are sunk in a well moistened peat in a glass-covered box or frame they will survive a surprising amount of neglect because they will soak up moisture from the damp peat and this has the effect of keeping the humidity constant.
Taking The Cuttings So far we have not touched the most important point of all for successful propagation - the time to take the cuttings. Unfortunately this is a most difficult thing to decide, for there are few reliable guides. Some say that the smaller the leaf of the rhododendron, the later in the year the cutting should be taken, but this can be no more than a generalization.
The most important thing is to take the new wood just when it is ripe enough, which takes years of experience and many failures to learn. For a beginner who has some plant he is specially anxious to propagate, the best way is to take one or two cuttings each fortnight of each month over a wide period until he finds the time at which they root the best. He can then note the results for future reference. Some rhododendron seem to root better without heat and without too much moisture; amongst these the types with thin, small leaves appear to fall.
The larger-leaved and softer types seem to prefer close conditions. One is constantly having surprises and disappointments, as when two apparently similar cuttings are given identical treatment and one thrives while the other fails. Possibly the two shoots had not ripened at the same time; even cuttings from different aspects of the same parent bush might not be in comparable condition. This illustrates the complexity and difficulty of standardizing propagating techniques. Now for the cutting itself.
How long and how big should it be? There are different opinions as to what constitutes a good cutting, but on the whole thinner, longer cuttings seem to take more easily than thick, short and sturdy ones. On the other hand, they must not be spindly and weak; very often the most suitable shoots will be found away from the vigorous front of the bush.
The length of the cutting varies according to the type.
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