Transplanting Young Rhododendrons
Rhododendron ABC's #14
As we continue our discussion on growing new rhododendrons from seed, we come to the third and probably most critical part of the process. This critical period occurs when the seedlings are two to three months past germination and have developed several sets of leaves. Until this time, they have been grown in a crowded, but still very protective situation. Now they must be weaned and allowed to grow in a less protective environment to the point where they can be set out and, more or less, fend for themselves. The analogy to the weaning and development of children from early childhood through their teenage years is striking.
The new and tender seedlings need to be transplanted into bands or pots and given enough room to expand into sturdy individuals. Several things must be considered for this all important event. Choosing the right growing medium is crucial. I do not recommend the use of prepared commercial potting mixtures, as these may contain enough alkalinity to stunt or even kill the seedlings. I rather prefer to use the two-layers (see ABCs # 12) and make the upper layer of "Nodamp-Off" sphagnum thicker than for the seeds, about 1/2 to 1-inch thick. This allows formation of vigorous roots with little danger of losses due to damp-off and other fungal diseases.
The next important procedure is to "tease" individual seedlings from the germinating mixture. This must be done very carefully, as the rootlets are extremely fragile and it is very easy to break and destroy them. I have found it helpful to use a pointed object, such as a sharpened pencil, to loosen the seedlings from the medium. Care should be taken to try to retain some of the medium on the rootlets, if at all possible. Also remember to block off a section of the seedlings and transplant from the block without any regard for selection. Don't just take the largest. Remember you are playing a lottery and chance is all important! At this point, there is no way to tell which seedlings contain the best traits.
After the seedlings are imbedded in the sphagnum they should be lightly pressed in and watered to settle the new growing medium around the roots. From this point, the seedlings can be treated as new plants. Flats containing the individual containers should be kept warm and provided with good illumination. Don't let the temperature rise too high, 70 degrees F is about optimum and never let the medium dry out. Weekly or biweekly watering with dilute soluble fertilizers work very well. I prefer to use about 20 percent of the strength recommended on the fertilizer container for mature plants. Try to keep a balance between over-watering and letting the mixture dry out.
If everything goes well, one should have sturdy plants several inches high within five or six months after removal from the germination mixture. At this point, the plants can be either transplanted to gallon, or larger, containers or can even be set out to selected spots in the garden. They are now on their own and one can sit back and, using usual maintenance, watch them grow and hope that at least some of them prove worthy of the care that has been lavished on them. Be patient! It may take 2, 5, or even more years for them to bloom but the satisfaction of seeing something brand new is worth the wait. You may even be lucky and grow a winner!
© All Portland Chapter content copyrighted 2011. Content, including photos, may be reproduced only with permission of the Portland chapter of the ARS.