If you look up a list of hygroscopic materials, you might find wood, salts, honey, and all other kinds of things involved in growing orchids, but not clay. That's because relative to everything else, clay is dense, and absorbs less moisture than any other kind of orchid medium. Salts absorb moisture due to them being ions; but clay is inert.
If the air could pull moisture out of clay, then the air could pull moisture out of roots before clay. However, orchids have air roots with no problems. If the moisture gradient in LECA media is wider than the zone off of a mount, then that proves that air "desiccates" materials faster than clay could.
So I don't want to say anyone is wrong, but I'll personally stick to my intuition until I see some cited facts, like maybe from a scientific review or a textbook or something.
But to answer the original question, I think LECA would dry out more under 50% RH than orchiata, sphagnum moss, Hygrolon, coco husk, etc. That's because clay gives up moisture, and absorbs it less readily than any of these materials do, in my opinion. Clay drying out does not mean it causes other things to dry out, it's the opposite. Maybe in a closed environment and over a long period of time, every non-living unregulated material would achieve the same equilibrium moisture, but certain things would take longer getting there.
Last edited by katsucats; 08-02-2021 at 12:30 AM..
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