In article ,
Chris Hogg wrote:

Years ago I saw a large rhododendron bed at a NT property that had
obviously been heavily manured with mushroom compost and was sprouting
a good crop of mushrooms. I was very surprised to see it, because
mushroom compost is usually heavily dressed with chalk to make it
alkaline. Perhaps the compost was lime-free in this case. How the
rhodies fared, long-term, I don't know.

There are relatively few true calcifuges and, as far as I know,
most rhododendrons are not among them. What they can't tolerate
is the very low availability of (I think) iron in limestone and
chalk soils. Adding a bit of chalk to other soils won't affect
them.


Regards,
Nick Maclaren.