In my experiences, with this method of soil-less growing, using hydroponics to root hoyas is the easiest way to root those sometimes impossible species. Certainly I am not able to root all my cutting using this method because it would be too laborious to then switch the rooted plants into a mixx for them to go to their new homes. But a select few will be added to this system throughout the year to ensure they root and not rot. As a rule, when I import a bunch of rooted cuttings from Thailand or the Philippines , this is the first place they end up for a few reasons. I feel that when hoyas are in this system, it is virtually impossible to over or under water them since the roots are tucked into some form of media that does not hold water for a longtime and allows for airflow above the plant and below in the reservoir.
This time I am experimenting with using a small form of Growstones which is made from glass but not sharp of shiny. I have medium sized nuggets also but chose to begin with the tiny stones. To the water reservoir I add rainwater, humic acid and Super Plant Tonic, which is an organic feed from Blue Mountain Organics. I run the pump 24 hours day and 7 days a week and I have the system near the T5 grow lights but not under them. It is positioned near a west facing window and has a heat pads underneath the tray that it is sitting on. Although the cutting appreciate light, I feel that being directly under the lights would mean they may dry out and become dehydrated since until roots have developed, humidity is their only form of hydration. I mist them at least twice per day being careful to not let the water sit on the leaves because too much moisture will still lead to rot.
If you are wondering which hoyas I have in this system they are: Hoya lacunosa ‘Langkawi Island’, Hoya platycaulis, Hoya linusii, Hoya lockii, Hoya lacunosa ‘Thai Clone’. I hope to follow up in a couple of weeks when these have roots and I am ready to add another tough bunch to the system for rooting!