When irrigation water is applied it immediately soaks the roots without any buffering from the substrate. So having the fertilizer water the proper pH allows the roots to absorb the nutrients efficiently quickly.
It takes roots under a minute to become fully saturated. No potting medium is ābufferingā the applied solution that quickly, so they always absorb at the chemistry that is applied. The pH effect within the pot comes in over time and reaction with the substrate, not instantly.
In the case of my rockwool phrag example, above, one can look at this scenario:
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 āfight against itā as the plant is trying to add to the negative ion concentration, and nature āhatesā 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 plantās efforts.
That process is not instantaneous; it takes time to have an effect. In pH-neutral substrates that are kept wet and flushed frequently, the accumulation of excessive ions, + or -, takes a very, very long time, if it occurs at all, and the use of a fertilizer solution at pH 6 or pH 8 is inconsequential, unless the particular plant has a special affinity for one ion over the other.
At high pH many nutrients are not available easily to the plant.
Unless the pH is so out-of-whack that it is likely damaging, thatās just plain untrue.
pH is a measure of the ratio of H+ and OH- in solution. If one solution contains 100 H+ and 1 OH-, and another contains 100-billion H+ and 1-billion OH-, the pH values are identical at 6. The first isnāt going to do anything negative to the plant while the second one might - due to the concentration, not the pH value.
I don't grow using the S/H method. I do use containers with side hole drainage about 3/8" up from the bottom to create a slight reservoir. I water 4-7 times per week with fertilizer. Never need to leach with pure water.
Sorry to burst your bubble, Lance , but that is THE definition of semi-hydroponics, as I conceived of it some 25-30 years ago.
If you have a decent pH meter or even sensitive test strips, I urge you to test the liquid in the reservoirs at various times after watering. If you water in the morning on a nice, sunny day, try it midday, just before sunset, and again just after sunrise the next day. I think youāll find that your carefully adjust solution pH isnāt as stable as you believe.
When I did that decades ago, I was astounded at the swings, whether I had irrigated with a pH-adjusted fertilizer solution or the same solution without adjustment. Thatās when I grasped that the plant, the substrate, and I suppose, the microbes that live in them affect the rhizosphere pH far more than do the solutions we apply, so simply stopped being overly concerned about it.
I guess maybe that is part of the challenge, I want to try to figure it out. Perhaps someday I will throw in the towel and return to bark culture but I am not there yet. I will take another look at the micronutrients and also the ph and see if I can find something that should be tweaked.
