JARS v41n3 - Pruning For Bushy Growth

Pruning For Bushy Growth
Weldon Delp
Harrisville, Pennsylvania

Reprinted from "The Rhodo Rooter", Great Lakes Chapter Newsletter. First published in the Great Lakes Chapter Study Group Newsletter, #8.

For the past three years I have been doing research trying to produce bushier plants in a shorter period of time. Now that I have succeeded in doing this I would like to share my findings with you.

Rhododendrons, as is true with other plants, have an inner power called restorative regeneration. This means that a plant is capable of restoring a lost part. A good example of this is the rooting of a rhododendron from cuttings.

This is the reason timing is so vital in the taking of cuttings for propagation, and each variety of rhododendron has its own prime time. The best time to take cuttings is from juvenile wood when differentiation is able to take place. In other words, a chemical growth substance known as Auxin-IAA passes from the leaf (primordial in a basipetal (downward) direction so as to promote root formation. This is why, when timing is not just right some cuttings may delay rooting, some may produce weak rooting, and some may not root at all, even with the use of IBA. Keep in mind that there are leaves (primordia) on the cutting itself. We can use the above information to great advantage to produce bushier plants in much less time.

A single shoot.
A single shoot.
Photo by Joe W. Jones

Apical dominance is prevalent in rhododendrons since they want to continue to grow up, and there is competition for nutrients between apical and auxiliary buds. Usually the apical buds win out. To control this dominance we have to take action.

Short stub pruning.
The short stub will help force multiple dormant bud breaks.
Photo by Joe W. Jones

Branching results from development of lateral or auxiliary buds - those present in the leaf axils. If we cut off, leaving approximately two inches of the juvenile stem without leaves (primordia) instead of cutting at the base, certain conditions will occur. Translocation occurs in the remaining stem. Auxins and cytokinin are transported downward to the auxiliary buds on the entire plant and nutrients from the roots travel up to the auxiliary buds and in a matter of days they respond and start to develop. You now realize complete breaking of dormant auxiliary buds.

If you are involved in tissue culture, you can get best results by pinching out the tips of lepidote rhododendrons the same way, and after five days remove the juvenile wood, strip the leaves, and make a new cut on top and bottom after sterilization. The auxiliary buds will break much sooner than the required four months in starting medium.

If you are rooting deciduous azaleas and are having difficulty getting the auxiliary buds to break then try the following: Four or five days before you want to stick your cuttings, pinch the tender tips from the cuttings. Leave cuttings intact on the plant. In four or five days remove the cuttings from the plant and stick in your rooting bed.