Growing Germinated Seedlings
Rhododendron ABC's #13
The last discussion focused on germinating rhododendron embryos (seeds) to form new seedlings. Keeping the seeds at about 70° F on moist, milled sphagnum, Nodamp-Off seed starter is really the easy part. The next step can be more difficult. "Growing on" or getting seedlings to the stage where they can be set out and treated as specimen plants can be fraught with a number of pitfalls.
I remove the light barrier from over the propagating case as soon as the first signs of germination occur. Seeds typically split their covers and produce light green sprouts which quickly grow into the germinating medium and produce two nascent leaves (the cotyledons). The transparent cover is left on the case to keep the moisture in. Water need not be added for several weeks. It is extremely important that the seed bed not dry out. Provision for plenty of illumination is thenext step. A fluorescent fixture mounted about a foot above the seed bed gives good results. A "Gro-lux" tube may be somewhat better than an ordinary tube, but the latter actually serves quite well. Some growers believe that a 12-16 hour light period, followed by a dark period, gives better results than continuous illumination. I have found the 24-hour illumination works well and find it more convenient. The important thing is light so that the plants develop strong, chlorophyll containing stem and leaves.
About two weeks after illumination begins, I begin fertilizing with a soluble fertilizer which is a good way to provide the extra nutrients the growing plants need. I have used Miracid with success. Begin applying Miracid at about 20% of the normal strength. Also you may begin uncovering the seedling box and allowing air to enter. Add the soluble fertilizer weekly and gradually increase the solution strength over time.
In about two to three months, these seedlings should have two or three sets of leaves and be ready to transplant. Even though crowded, the germination container has provided a very protective situation. Transplanting is critical and may result in heavy losses if precautions are not taken. The steps and conditions for transplanting, which can be compared to weaning in the growth and maturation of mammals, will be discussed in the next issue. If done carefully, one can have vigorous new plants ready to challenge natural conditions in the landscape in from eight months to a year after the seeds are sown.
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