1. It is only the H. macrophylla and H. serrata that do this
2. H. paniculata and H. arboescens will not change color with changes in pH.
soil that contains no aluminum, will never have blue flowers, no matter what the pH
Thank you
@Gemini for taking the time to post this information, much appreciated.
I have been researching Hydrangeas for several years now, partly because my Mum grows them so I am able to have case studies but also because I was curious as to why they are able to change from pink to blue.
What I have read quickly in your post (I have not watched the videos yet) runs true to what I have found. I did not know that the colour change was limited to only some of the species, but I was aware that the acidity or alkalinity of the soil was what dominated the colour that the flowers bloomed in. Again, I was aware that Aluminium Salts were also a contributing factor to the colour of the blooms.
So why was I interested/concerned in why the plant was able to change the colour of its flowers?
I have always been interested in growing a purple coloured cannabis plant. Because of this, I researched what it was that made the flowers change colour. Hydrangeas are probably one of the most obvious plants to be able to do this, so I used them as my basis for the research. Quickly I learned about the pH of the soil/medium and the Aluminium Salts. On a trip to my local grow shop, I explained to them what I had discovered and we looked at the ingredients of many of the flower boosters on the shelves.
The only product which held claim to bringing out the purple in strains that already had the purple phenotype was "Purpinator". PH neutral with a pH of 6.0 and contains no Aluminium.
With what I have learned and with my limited experience the best natural way to bring out the colour in cannabis is to lower the nighttime/lights off temperature. Previous to this I would keep my nighttime/lights off temperature within a few degrees C of my daytime/ lights on phase. By keeping the nightime/lights off temperature so close it to the daytime/ lights on phase it promotes bushier plants with closer nodes and they experience less stretch during the first 2 weeks of the 12/12 lights phase. I also continue to use my metal halides durinng these first 2 weeks as the lack of red also lessens the "stretch". However, if you do try this method I would suggest turing on one high pressure sodium light for 30 minutes before the lights extiguish. The 30 minutes of the red spectrum that the plant recieved will help it "go to sleep quicker" enabling the plant to utilse more of the nightime/lights off phase.
For more information on this strategy research,
Emerson effect
en.wikipedia.org