When I was younger, my great grandmother used to have a number of hydrangeas in her yard in Savannah, GA. Some of my other family members had hydrangeas in their yards but they were all different shades of blue, purple and pink. I was told that you put rusty nails in the soil around the bush, the flowers would turn blue. To get pink flowers, one was supposed to put lime in the soil around the bush.
Yesterday, I was outside enjoying the great weather, when I noticed a group of flowers in my front yard. They were in one group but I noticed that a couple were a light pink while the rest were dark blue. They didn’t look like hydrangeas, but I thought they might share similar color characteristics.
I did not find what species these flowers were, but I did find more about hydrangeas. The process by which these hydrangeas change is cited by a couple sites to operate in a couple ways. A couple sites said that the color change was on account of the pH, while a couple said that this color change was due to the concentration of aluminum in the soil. Three colors, pink, blue and white, can be seen with hydrangeas. White hydrangeas, according to the sites I found, obtain their colors hereditarily, and soil conditions cannot change flower color. It was also noted that intensity cannot be changed, that this related to genetics and general soil quality.
For pink hydrangeas, the plant should not intake any aluminium. Adding lime will help this by keeping the pH around 6.1. The lime discourages the uptake of aluminum. Also, fertilizer with phosphorus helps prevent alumium as well.
For blue hydrangeas, the plant should be in soil that has plenty of aluminum present. This can be done by adding aluminum sulfate. The pH should be in an ideal range for this, so adding coffee grounds around the hydrangea will give a pH of about 5.3. Fertilizer should be applied that has high potassium and low phosphorus.
Note that in this picture, there are several colors in one plant. This was what I observed in the flowers in my front yard. Could this be from differences in pH from different places around the roots or some other factor?
If you were to plant these to obtain a certain color, it was advised that you first preform soil tests and get an idea for the pH of the present soil. It also suggested that you don’t plant these plants near sidewalks because of the concrete material that may dissolve and runoff into the soil, which i thought was interesting.
So, the advice of my great grandmother was not far off. By adding rusty nails to the soil, which are aluminum, it makes the flowers blue. I was told that the color was achieved because of the pH, but the pH only regulates intake of the vital micro nutrient, aluminum.