… Bag says 5.5-6.9 so quite a window ...
Not heard of that Plagron stuff. I am using straight PT Horticulture Pro-Mix HP which is sphagnum peat moss, lime, perlite, wetting agents and mycorrhizal fungi.
I went though that same "what's the best pH" and was also a trite confused. So I did my own tests. I grew the same two strains in the same environment (temps, humidity, air flow, nutes, etc …) and the only thing I wanted to change was the pH. So I have tested with pH values of 5.5, 6.0 and 6.5. The 5.5 and 6.0 grows were still very good as far as final effects. But ...
The pH of 6.5 seemed to bring out a little bit more in these strains. The trichomes glisten a little bit more. I am testing some of the LARF and it has a little bit more of a robust flavor. And the chopped flower is just a little more stinky when I'm rolling 'em up.
My source spring water is pretty alkaline at pH 8.9 and 5 ml (1 tsp.) of 18% phosphoric acid in an imperial gallon lowers the pH to 6.5. I did use 7% pickling vinegar to lower the pH until a couple of days ago. That's when I read that both citric and acetic acids will work in a pinch but neither are stable enough to maintain the lower pH for more than about 24 hours. If that ...
I am going into flower now and have only one watering with the phosphoric acid to pH down. In about 3 months, I'll see if H3PO4 helps to further improve the finished product.
