OAKY,
Great observation. You seem to be very in touch with your plants. Good sign of a great grower.
The production of anthocyanin or the lack of happens to be of special interest to me, most specifically in table grapes.
In Mexico, there is very big problem getting the red or purple color (Anthocyanins) in red, purple or black grapes. Their magnesium is off the charts, with heavy Mg in the water and in their soils and most growers applying more and more since there is none in their leaves...they believe it is trapped in the soil... (I used to say the same thing for more than 20 years). Mg pushes out Ca.
Here in Peru, the problem is exactly the opposite, all the colored grapes (sounds racist) are all too dark.
Anthocyanin is made by the plant to "SPECIFIC STRESSES". Not all stress causes the plant to make anthocyanins.
On a scale of 0-14, the irradiation level here is 15. That is a serious stress. Burns everything.
Here in Peru, naturally occurring there is some 400+ppms of K in the soil. High K makes the fruit darker.
Here in Peru, there is low to medium P, 40 to 80 ppms. Everyone that I help likes 400+ppms of P much better..... and the fruit does not darken as much. Labs are used to reading off charts, not matching K to P. That concept only came from one man, Carey Reams, who in my mind was a genius.
Here in Peru sodium issues are huge, as are carbonates and bicarbonates. Higher pH makes P availability goes down. All the above issues push pH up.
K looks just like Na to the plant, so there is reason to believe that high K and Na vs P levels is highly suspect, not just high K.
Without enough Zn and Mn, plants can have enough P but can't use it correctly.
And then of course there is Ca. And yes, getting Ca up high really seems to help. Where we have high Ca (83-86%) in the colored grapes, the color is EXACTLY as it should be.
Personally, everything that I have ever tried that had purple in it wasn't too good....
