As Semi-Hydroponics seems to be catching on, I want to make an observation from my own experiences after reading of some people’s trevails with the method on some of the online Hoya forums. I don’t think that it is possible to overwater in semi-hydro, but I do think you can easily underwater. I am currently watering all of my s-h plants daily even when kept in a humid environment. I do not really believe that hydroton will wick up from the resevoir all the way to the top of the substrate. If your plant’s roots do not extend far into the hydroton, and you are watering less than once per day, I do not think you are watering enough.
In true hydroponics, a nutrient solution is being pumped, or sprayed many times per day on to the substrate. I do not believe there is enough wicking power to get the moisture from the resevoir to the upper medium unless your roots extend all the way into the resevoir. I also have real concerns that S-H will not work well with central heating systems in the winter. I believe that the environment will be too dry, and unless you have the ability to water more than once per day, your plants will suffer. Here is a photo taken two days ago of Hoya praetorii growing in semi-hydro and watered once per day.