I hope she won't mind if I jump in on that question...
I have been doing a lot of research into orchid nutrition lately, looking at it from the role of the individual nutrients, how they interact within the plant, how well they are stored by the plant for redistribution to other parts of the growing tissues, and how available they are in the ecosystems in nature.
To summarize - most plant nutrient research has been done on food crops like rice and corn, which grow orders-of-magnitude faster than orchids, and originate in totally different natural ecosystems, so have different (much greater) nutrient demands. The fact that the vascular fluids of orchids tend to be much more dilute (on the order of 25%) is another indicator that the nutritional demand ought to be lower.
The extremely small amount of research on epiphytes suggests that the nutrient supplies in their natural environments are 1) meager, 2) more-or-less constant, 3) far less balanced than that terrestrial plants see, favoring N over P & K, and 4) calcium and magnesium - taken together - are very important. There is supposed to be an article in the March AOS magazine on this subject - not mine, but I have contributed.
So based upon that, I have surmised - and am using fertilizer almost every time I water, but at a concentration of at most, 50 ppm N. I have been feeding my plants at that rate for over a year now ( K-Lite formula), and am quite pleased.
If you divide 4 by the %N on your fertilizer label, the result is the teaspoons per gallon to mix for 50 ppm N. for you metricated folks, 5.2 / %N = ml/L.
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