Nicholas, you certainly "nailed it" on the "opinions" part, but plant nutrition - especially when it pertains to orchids - is poorly understood and open to a lot of interpretation. Bill Argo, the PhD in this field that invented the MSU fertilizers, told me that "nobody really knows what's going on in this area".

I have been doing a lot of reading in the area, and am licensed to produce fertilizers, so let me share a bit of my take on what I've read:

Orchids roots are very good at absorbing nitrates and ammoniacal compounds, so most orchid fertilizers use those; nitrates more heavily as they tend to promote more compact growth. Roots do not take up urea well at all, so it must decompose to ammoniacal compounds before absorption, something that does not happen efficiently in orchid media. However, urea is preferentially taken up through areas in leaves known as plasmodesmata, while more polar species like the other two nitrogen forms are not. You will find that urea "greens up" plants well, but many of the other necessary nutrients are not well absorbed that way, making foliar feeding less desirable in orchids.

There is a lot of debate over nutrient formulas.

The MSU formula was actually devised to disprove the concept that high phosphorus promotes blooming (plus the need for calcium and magnesium). That myth came about as marketing hype (or misinterpretation of test results). When Mir-Acid (30-10-10) was invented and marketed for orchids, it was noted that they grew beautifully. Unfortunately, it was later noted that they didn't bloom very well. Inexpensive phosphorus compounds were added (diluting the nitrogen level, which is known to quash blooming) and - voila! - blooming resumed. It was then marketed as a bloom booster, even though it didn't boost anything, just stopped stopping blooming.

Grow a plant with excellent overall culture, and it will bloom to its genetically-programmed maximum capabilities; nothing will boost it further than that.

There is some thought that excessive potassium may (and I stress the uncertainty that "may" carries) cause long-term health effects in orchids. I am one of about 200 people worldwide that is experimenting with a derivative of the MSU fertilizer called "K-Lite". So far, so good....time will tell.

And I do mean time - if you feed regularly (you should, more on that later) - changes in the diet will take a VERY long time to become evident, and many nutrients are translocatable within a plant, so even if you are deficient in something, the plant can transfer it to new growth from old. Calcium and boron are exceptions, so they must be provided regularly. By contrast, if you are poor at feeding your plants, almost any change will show results (which is how new fertilizers often get labelled as "miraculous" by folks who are suddenly paying attention to that part of their regimen).

I am convinced that choice of fertilizer formula is the "fine tuning" part of the equation. Of far more importance is regularity of application and a low solids content of the applied solutions.

If you think about an orchid in nature, it gets that vast majority of it's nutrients from the rain cascading though the forest canopy and trickling down the tree trunk. That happens very frequently, but the concentration is very dilute. (I have read some measurements of 15-25 ppm TDS - total dissolved solids.) Also, the concentration is naturally highest JUST when if first starts raining - and Lo! and Behold! the velamen on the orchids' roots has apparently developed a way to trap ionic compounds almost instantly upon their absorption by that spongy layer, preventing them from being diluted or washed out by the rain that follows.

That has led me the following regimen:
  • I always use pure (reverse osmosis) water, to keep my solids content as low as possible.
  • I feed at every watering - 2-3x/week in summer, less in winter, mostly dictated by the weather and light level in my greenhouse.
  • I use a fertilizer concentration of 35-50 ppm N (Divide 4 by the %N on the fertilizer label. The result is the teaspoons per gallon to use; I round down for measurement simplicity and to err on the weak side.) There are several grower I know who use 20% of that, watering daily.
    Even that lowest level is many times stronger than they see in nature, but we ARE trying to grow them better, aren't we?