Good name, Ray--the Goldilocks Principle, neither too wet or too dry. Here is how I would state it: "Healthy roots are critical to orchid plant health. The velamen covering the roots is kept healthy by maintaining an acceptable ratio of air and water at the roots. This ratio may vary between genera or even species in a genus. The variables are the medium, the container and the ambient humidity in the growing space."
As Ray knows, I've been playing around with various plants in Semi-Hydro, and the above is the conclusion I have come to, regardless of medium or growing technique. Orchids are epiphytes and like to have humid air at the roots. The closer we can come to that, the better. So I'm not surprised at the photos of the roots above, particularly if grown in a decaying organic medium (Pinus radiata or Orchiata or similar seems to decay more slowly than most of the fir or Doug fir mixes). But even in S/H there is variation among genera. Some genera (Miltoniopsis is a good example) have fine roots and seem to like to be wet, unlike Catts and the monopodials which appear to like more air at the roots, so for some of them (like Catts) I will do exactly what was illustrated here, except using S/H, and so far the result is good. I think Phals may like this as well (though they also like heat at the roots). I go a bit further with Tolumnias and Vandas, which are placed in an empty plastic net pot surrounded by moss inside another pot (clay or S/H) to keep the humidity good around the roots. So far so good.
As for the top layer of leca in semi-hydro (the advantage of leca appears to be its shape as much as its composition, as it allows more air around the roots). The disadvantage is that the top layer can stay too dry. I'm trying both NZ sphag as well as live moss (I live within sight of Puget Sound, so no lack of this, we aren't called mossbacks for nothing, particularly this winter). I added this layer to my Paphs and Phrags a few months ago, and when I checked themthe other day they really like it with lots of new growth (of course it's also spring here and I use bottom heat until it's warmer). New roots of course come at the top of the transition from root ball to plant and so they like something damp to go into, much as they do in nature.
