Are Rhododendrons roots poisonous?

Moved into a new house a year ago which has a wonderful established beech hedge fronting the road.  It is in the deeds of the house that we have to keep it maintained and at a certain height, etc.  Indeed the road is Beechway and was named after the hedge!

Between the house and the hedge there was a 4ft area of grass with nothing growing. I have planted 5 rhododendrons which look wonderful but now am worried that they may affect the beech hedge which would be a disaster!!!  My husband says he thinks he has read that their roots can contain chemicals poisonous to other plants.  Any advice gratefully received.

Yes, they do - if you see them in the wild, then nothing will grow underneath them.

In your situation, it rather depends how large they are compared to the beech hedge, and how large you intend to let them grow. If you intend to keep them smaller than the hedge you should be OK, but planting them so close they may not thrive because of the hedge's roots and its demands for water.

Nothing will grow under them but I have never heard that they are poisonous.  I have known them grown as mixed planting with trees with no detrimental effect on either, including planted very near to a beech hedge.  Just remember to make sure there is enough room to trim the beech hedge, it will have to be done at least once a year.

Sorry, I meant that they are poisonous to other plants in the sense that they prevent things growing near them.

As far as I understand it, Rhododendrons do not secrete anything that is poisonous or toxic.

Nothing will grow beneath Rhododendrons, simply because of the dense shade they create. This will be especially true with groups of Rhododendrons which merge together, and create a dense shade cover over a wide area. Everything beneath them will die.

This monoculture also has the effect of depleting some of the mycorrhizal bacteria in the soil, and that makes it difficult to establish other plants after Rhododendrons have been cleared. It takes time for bacteria to reestablish themselves.

One or two Rhododendrons shouldn't be a problem.

That's interesting, Gary, and makes perfect sense.