I have made many mistakes with potting mediums over the years. I once lost half of my collection to a change over to a “new miracle” potting mix. That particular mix relied on a material called Turface mixed with bark fines. It was so heavy that is became impossible to determine when to water by picking up the container. The top inch would be bone dry, and below would be soaking wet, which rotted off all of the roots in no time. I also tried out the “semi-hydro” method of growing with very limited success. Feel free to experiment, but do it in a very limited way. It is hard to argue with my success with the medium that I use on almost everything. If you live in an area similar to mine, I would try to model your “soil” after mine.
My mix is comprised of four parts #4 perlite (large sponge rock), to three parts fine orchid bark, to two parts peat-based potting soil (I use Pro-Mix). To this mix, I thow in a handful of powdered limestone, and a couple of handfuls of horticultural charcoal. That is my chunky mix that pretty much works for everything. It allows quick draining, and retains enough moisture and oxygen for the plants to thrive.
**UPDATE**The formula has slightly changed since I first wrote how I make my original mix. Now I have added Tree Fern Fiber, but you really can’t go too far wrong with either potting mix. The main thing to keep in mind is to keep the mix chunky with lots of aeration. I also have warmed considerably on the semi-hydro method of growing Hoyas for many of the difficult ones. Here is a new video of my mix with all of its various components: http://youtu.be/_VQAnhFAHUg
A note on potting mixes: All potting mixes fail over time; they begin to breakdown and they hold far to much moisture, which can quickly rot the roots. I feel strongly that almost every Hoya needs to be repotted at least every two – three years. Many will need repotting annually. When re-potting try to hose off as much of the old mix as possible.