But do they really like it?
I'm wondering about that! Paphs grow in moss over limestone because it's there already I think. Maybe they would like it better without limestone. There are rupicolous laelias that grow in rocks rich in iron, not because they like iron. And if epiphytes have gone up in trees, it's because they had no choice. That's where they had to go to get fresh air an sunlight. You put them in a pot and they'll be very happy for the most part. The same for me, I grew up in a cold climate, but if I had had a choice, I would have preferred Hawaii. All I'm saying is we must look beyond the obvious. That's why orchids are so tolerant of our cultural practices, houses and greenhouses conditions. They're like the Borgs in Star Trek : they adapt. I wonder if there was ever a serious scientific study about oyster shells effect on paphs. There are orchids of course that are really difficult to grow well like Disas and many Cypripediums. I once bought seeds of Banksia from South Africa and they came with a patch of rose paper bathed I suppose in smoke from brush fires. They needed it for germination. Talk about tough customers!