Question about trimming Rhododendron and Japanese Yew ??

I live in the mountains at 4200 feet above sea level. I have many Rhododendrons that are about 30 years old, and I also have four Japanese Yews of the same age. All of these plants are very healthy.
Last summer, I decided to trim four of the Rhododenron, and two of the Japanese Yew. All of these plants were getting so tall that it was getting very hard for me to lightly trim the tops of them. I would say that I cut about 1/3 off the top of these plants. The trimming was done last August.
Now, two of the Rhododendron are dead. I have cut back the bark, looking for green, but they are totally dead. I have read, and I have had others tell me, that you can trim these plants down to just 12 inch stubs off the ground, and that they will survive.... But such was not the case for me.
On the Japanese Yew, they almost died, but had some signs of greenery in some branches. I have babied them back to life, so they are going to be ok. However, I am now afraid to trim more than the new shoots of these plants in the future, for fear they will die, but in several more years I will not be able to reach the tops for trimming !!
Any thoughts, or ideas ??
Thanks !!
James
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"James Nipper" wrote:

You should have done your research before the fact... I bet it never occured to you to ask questions *prior* to NIPing into those plants. http://www.rhododendron.org/v47n2p79.htm Well, they're dead now, move on.
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Hi James,
Some people do that and have no trouble. However, the director of Tyler Arboretum here in SE PA said that experience has shown him that it only works on plants that are healthy and in a fair amount of sun. Those plants in more shade sometimes do not respond.
Rhododendrons have dormant buds. A healthy plant in a partially sunny location will usually sprout some of these dormant buds when you severely prune them. However, since light seems to be the main stimulator to this new growth, plants in more shade don't get enough light on the dormant buds to stimulate them.
Plants that are diseased or in more shade also may have black insect scat, mold, lichens, and other stuff covering the dormant buds preventing them from getting stimulated by light and sprouting.

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Thank you Stephen !!
James
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