[JLu]

LouisW, you have opened a never ending controversy. There are believers on all fronts of this issue and you will get all kinds of replies to your question. No one has all the necessary data to prove their position.

So my belief (and I think it's mainstream thinking)....plants use a lot of nitrogen so they need enough for optimum growth. Personally, I use 50-75 ppm nitrogen at each watering. There are some excellent orchid growers who use 125ppm and I can not say that's wrong. At least one Paph authority says Paphs need no fertilizer whatsoever. I don't buy that. However...nitrogen promotes foliage growth and too much (whatever that is) can result in lots of foliage and no (or reduced) bloom. This effect (foliage with reduced bloom)is widely believed across horticultural interests and I believe it.

Phosphate is a more controversial and potentially dangerous issue. Even though P is a macro nutrient, it is needed in smaller quantities than nitrogen. You can actually kill plants and permanently poison soil with phosphates. Admittedly, this is unlikely with orchids where they are potted and flushed frequently, but absolutely in soil phosphates can be bad if over used because they are not mobile (do not leach) in the soil and accumulate over time. I'm going to say (with expectation of some criticism) that so-called bloom formulas are rip offs and do nothing good with a huge potential downside. I recommend against them unless you know by foliage analysis that you have a P shortage.

Remember, in the wild, most orchids get slight fertilization versus their terrestrial counterparts, so they are evolved in a nutrition poor environment. I think that also suggests not falling for fertilization schemes intended (but not necessarily suited) for regular garden plants.

You'll get every suggestion on earth here. This just mine.