Rhododendron

Hi Alexandre,
You want to know what we call the ground in English, we call it soil or earth, I hope that is what you mean.
We only cut back Rhododendrons when they are overgrown, it is a waste of growth when you can layer them. You need acid soil for Rhododendrons.
Hope this is what you need.

No no the grown used for the Rhododendron the acid soil we say in France << Terre de Bruyère >>

I think you are saying that you would not use acid soil for Rhododendrons, you need soil which is below PH4.