Pale leaves with green veining

[Ray]

If you are open-minded enough and wiling to take definitions to extreme, one might consider all orchid growing to by hydroponic in nature, or nearly so, as for the most part, the substrate primarily provides mechanical stability and temporary moisture storage while the nutrition comes from the applied solutions.

 

[Roots]

I am learning so much from reading this thread. I want to go back to school and study water chemistry.

Sounds like you’re on the right track. Just remember as long as paphs have good moisture they don’t tend to spontaneously die so keep perfecting things but don’t let it freak you out if you’re not 100% right

Thank you for the words of encouragement. I got my first two paphs one year ago this month and am feeling a bit frustrated with what seems like my shallow learning curve. On the other hand, I am finding the challenge highly entertaining.

When a plant absorbs a negatively-charged nitrate ion, it must secrete another negative ion to compensate. Ammonium ion absorption (+) results in a positive ion secretion.

The untreated rockwool has a high pH, indicating the presence of excessive negative ions. If the plant must secrete negative ions, the substrate chemistry will “fight against it” as the plant is trying to add to the negative ion concentration, and nature “hates” imbalances. That resistance can stifle the natural processes within the plant, potentially causing issues. If, on the other hand, the plant, due to it being fed with positively-charged ammonium ions, must emit positive ions to compensate, the substrate will favor the absorption, supporting the plant’s efforts.

This is a beautifully clear explanation of how nitrates and NH3's and 4's (is there a difference between these?-aside from the additional atom) move through the plant and substrate. Thank you.

N is usually provided as around 95% Calcium nitrate/potassium nitrate with the remainder being ammonium. This is due to the lack of CEC of most hydroponic substrates (leca being one) and eliminates the possibility of ammonium toxicity.

I really should quote everyone here. I think I need to experiment with different fertilizer solutions to see which form of N is preferable. Peter's is not high in NH3-4. However, about half of the N in my solution has been coming from additional urea, which when broken down by microbes becomes ammonium and carbon dioxide-I think. I shouldn't have high microbial action in leca but I have been using quantum. So possibly ammonium toxicity?

With coarse leca I cover the surface with moss to reduce evaporation and provide a moist layer to accommodate new surface roots.

I am now moving beyond the nutrient deficiency question but if you have the time, could you talk a bit more about the moss? How do you introduce it to your pots? I am assuming that it survives on the surface because of your frequent watering? I do feel that the surface of my pots is dry and I worry about new root growth. But my N is really too small to comment.