Amey , what do you say to the theory that fertilisers containing urea are useless to epiphytic orchids, because the urea has to be broken down before the plant can utilise it- normally done by soil bacteria which are not present in epiphytic composts ?
I know two orchid fertiliser manufacturers who are of this belief, and consequently use nitrates in their mixes , shunning the much cheaper urea.
It is a matter I could usefully take up with one of those firms - for whom I sometimes act as consultant but if I am challenging their experience and belief I need to be quite sure of my ground, preferably with some references ?