I am prompted to ask this question because of Tina's post about Hyacinth color.. Didn't want to hi-jack her thread by posting this as a reply there.. Some years ago I read some 'expert's' blurb to the effect that soil PH affected the color of Hydrangea blossoms; accepted their statement as gospel so never attempted any experiments, as Jerry would do, to verify the statement.. But recently I've come to question that info, soooo, do any of you know for sure if this is true; relative to Hydrangea or any other flower? I am fully aware that soil PH levels are or can be very critical to a plants overall health.. Thanks for your input on this.. Love to all, Hank.
Tis true, tis true. The lower the pH the bluer the flower. The closer to neutral the pinker it is. Soil at 4.5 will produce a deep blue while 7.0 will produce a deep pink. My hydrangea is a light to medium blue as the pH is about 5.3 around the bush. Jerry
Thanks to both you, PiO and Jerry for your replies.. So I can return that bit of info to the 'known facts' list in the horticultural file in my mind.. Hank
Well, the answer to your question is, “yes”. Soil pH has everything to do with Hydrangea flower colour. Simply put, the more acid the soil is, the “bluer” the blooms will be. The more alkaline it is, the pinker it will be. Perhaps it would be helpful to understand why this is so. Naturally, not everything in nature is clear-cut or straight forward; there are other factors, but I will get to those in a moment. For now, let me stick to the soil pH and bloom colour. How it works: Soil pH is not the only factor, there is a missing link: aluminium (or iron to a lesser degree). They are the two most important aspects of this scenario. It isn’t actually the acidic pH that gives Hydrangeas their blue colour, it is the aluminium (or iron). What then, is the relationship here? Why do I mention both these elements in the equation? First of all, the aluminium—this element is not a nutrient that the plant requires to grow, produce flowers or seeds and so it is not taken up actively as are micro and macronutrients. So what IS its role then? The aluminium must be taken up into the plant in a passive manner...per osmosis. Once taken up into the plant’s circulatory system, the aluminium collects in the petals. The pH makes this process possible. In order for the aluminium to enter the plant’s roots, it must be in a soluble state...this is where the pH comes in. The lower the pH, the more soluble the aluminium will become so that its ions will pass into the roots via an osmotic action. The more acidotic the soil is around the roots, the more ions will be moved into the plants system and thus the darker the blueness of the flower petals will become. This subject of Hydrangea flower colour is like a path with a bifurcation. At the bifurcation of “flower colour path”, there is one branch that leads to blue tints and the other leads to a pinkish tint. As far as I know, white Hydrangeas cannot have their colour modified at all by pH and aluminium manipulation. The pink colour: This will occur when the soil is alkaline (has a pH greater than 7). The alkalinity means a high pH, and the uptake of aluminium ions is effectively blocked. Of course; armed with this knowledge, one can adjust the colour of their Hydrangeas to a degree. The change will require the gardener to exercise some patience, as the change will not take place over night, and it is always unpredictable. Trying this technique in a container will be easier to do and perhaps take less time because the gardener will have full control of the root’s milieu. Esoterica: As mentioned above I have a few words to say about other aspects that determine the flower colour in Hydrangeas. pH and aluminium are not the only reasons that determine Hydrangea bloom colour. It is perhaps easiest to look these other factors in a basic way: 1)The genetic make-up of any given Hydrangea plant (its heredity). The genetic makeup can dictate what tint the plant’s flowers will lean towards becoming. 2)Light exposure—Where the plant is situated. How much sun and/or shade. 3)The sun’s radiations will also cause a pigment change. (This is related to nr’s. 3 and 4). 4)The age of the flower—The older a flower is (in terms of the progress of the season) the more noticeable the colour tint change and petal thickness will be. 5)The health of the plant—The healthier the plant is, the more intense the colour. This is why some folks fertilize their Hydrangeas. 6)Weather conditions. The colour intensity can be affected by temperature. 7)An interesting note—I read an article last year about how it is thought that Hydrangeas (and other perennials) can “mutate”, shall we say-- adapt to their soil, light and other milieu factors, manifesting this in their leaf structure, flower colour and habitus. It was a very interesting hypothesis. I wish that I could recall where I saw that. Aside from the effect that soil pH has on bloom colour, it also effects feeding abilities of the hair roots and what micro and macronutrients are taken up by them...or for that matter inhibited. All very interesting to you, I am sure ...but that is off-subject here.
Thanks much, Sjoerd; your reply is exactly the type of information that I like and need.. Yes, indeed, your #7) note opens the possibility of some extremely interesting research and conversation.. Hank
