(Pssst. Psssst. - starting out a post by pretty much saying that everyone here is a dunce about feeding will not encourage folks to read more and may piss a few off.)
I find your post to be unhelpful, as you have no factual information backing up your claims and except for what Fred Clarke does, no numbers about what you think is correct.
Here is the logic I have used to come to my regimen:
- In nature, epiphytes get the majority of their nutrition when the rains wash dust, droppings, and canopy tree exudates down onto them. The concentration of those nutrients is minuscule and is only present for the first few seconds after the rainfall begins. After that, it’s pretty much pure water.
- The mass of nutrition captured is determined by the concentration in the throughfall and trunk flow, coupled with the volume of velamen on the roots. Once the velamen is saturated, nothing more is captured.
So the nutrition supply is a tiny concentration, absorbed by a finite volume, but can be taken up frequently. I copy that in my feeding regimen, preferring to feed a dilute solution, frequently, as that is what the plants have evolved to expect.
Then there’s the mass of nutrients required.
All plants, as far as I’m aware, use the same chemical processes to fix carbon. (C3, C4, and CAM may differ, but that has to do with collection and storage of carbon dioxide than the underlying conversion process.)
In order for those processes to add one pound of mass to a plant, it must take in and process about 25 gallons (~200#) of water and only about a teaspoon (~5 grams) of NPK nutrients.
Corn (maize) might gain that much in a week in the middle of summer. A phalaenopsis might add a pound of mass over the span of several years.
If, for the sake of argument, we select a 4-year window and assume the plant will absorb 100% of what is applied (completely fallacious, but bear with me), that would mean that we could feed it about 1 gallon per week of an 11 ppm (TDS) solution. However, if you add that roughly 95% of the water absorbed is lost to transpiration, that means our solution could be only 0.6 ppm concentration!
Thinking back to the exposure time and capture volume, which limits the uptake per watering, and realize that there is also a limited amount of continued uptake from the surrounding substrate, it seems a sure bet that such a regimen would starve the plants. We compensate by increasing the solution concentration and by our feeding schedule.
We can calculate the volume of the velamen on a plant by measuring the total root length, outside diameter, and thickness of that layer, but that’ll vary by type of orchids, size, maturity, etc., and I’m not about to chop off roots to do that.
So, instead, after over 50 years of experimenting, I have settled on the application of a 100 ppm N solution once a week. For plants in moist, water-holding media, that seems to be a pretty good level, and I don’t see a lot of death in my collection. For bare root vandas, knowing they only get fed while being irrigated, I might increase the frequency.
Being that all plants have the same nutritional demand for growth, that suggests that vandas being “hungry” is as much about their uptake capacity per feeding as it is their growth rate.
Hybrid Mode
