I’ve never stated that Semi-Hydroponics is the “be all, end all” of orchid culture, or even “the best” was to grow them, but I am thoroughly convinced that it can offer tremendous ease and convenience. That does not mean, however, that it is “an automatic”, as some folks have difficulty with it.
In general, I find that folks that have issues with plants in semi-hydroponics seem to hit one or more of a relatively small range of shortcomings in their application:
Improper timing of transplantation.
The simple fact is that plants must grow new roots that are tailored to the new environment, as we fully expect the old roots – those that were tailored to the old environment – to fail and die. (A subset of this being those that think it’s a way to rescue ailing plants that they don’t know how to grow in the first place.).
It is important that the pots always be filled rapidly to the top to allow the natural flushing action to take place. Merely “topping up” the reservoir is a sure way to accumulate and concentrate minerals and plant waste products in the medium, poisoning the plant.
Letting the pots dry between waterings
Which makes it no longer ‘semi-hydro” at all, just traditional culture in inert media. Unless you flush periodically, minerals will build up rapidly with that type of treatment, again resulting in poisoning the roots of the plants.
Growing their plants too cold.
The open, airy, and moist environment of the pot may lead to evaporative cooling, depending upon the rest of your growing conditions. This is primarily an issue with phalaenopsiss, a genus that folks seem to forget are really “hot” growers, but can be applied more broadly.
Another thing I’ll add – but something that people need to grasp no matter how they are trying to grow their plants – is a thorough understanding of what “orchid culture” truly means, especially understanding all of the aspects it involves, and how they interact. Light levels, humidity, air movement, temperature and its variations (day/night, and seasonal), watering and feeding regimen, and even something as seemingly innocuous as your personal tendencies when it comes to “messing with” your plants, can affect how well you can grow them. ANY change in how you grow requires that you rethink the overall effects and interactions of all of those aspects, and many folks think “S/H” encompasses it all, rather than merely moisture delivery and avoiding medium decomposition.