I think Ray put it most eloquently in another post - here is his response to wet medium -
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"The important aspect to consider is what effect the water retention of the medium chokes off air flow to the roots. If it's fresh, fluffy, high-quality sphagnum, it is hard to overwater it to that point. Older, poorer quality stuff compresses really well, as does old, decomposing non-sphagnum medium.
Consider that water exists in the medium in two forms (or places)- that absorbed by the medium (and not contributing to root suffocation), and that held by surface tension between the particles. That is known as "bridging water" as it bridges and closes the airflow pathways through the medium, leading to suffocation, death, and rot.
When you let a medium dry between waterings, you're not - as we have all been brainwashed into thinking - doing that because the plant wants to be dry, you're doing it to let that bridging water evaporate or get absorbed, so you stop suffocating the plants' roots! (Hence the reason for a good, open medium .)"
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Ray Barkalow
First Rays Orchids
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