Like many other types of flowers, hydrangeas are available in various colours. When you plant roses, for example, you will either select the plant or seeds based on the type of rose as well as its colour. The colour of the flower is already determined in most plants. However, when it comes to hydrangeas, this is not the case.
When it comes to the colours of different hydrangeas, pH plays a significant role. Everything in our environment and even the human body itself has a fluctuating pH level and there are many factors that influence these levels. Most of which being environmental. Soil pH levels range from 0 to 14. Acidic soil measures between 0 and 7 while alkaline soil measures between 7 and 14. In general, the ideal pH level for any plant is around 6.5.
Blue hydrangeas are associated with a greater presence of aluminum whereas aluminum is absent in pink hydrangeas. If the colour is in between pink and blue, then there is some aluminum found but not a large quantity.
Aluminum levels and pH levels of the soil are very much connected. This compound is usually found in greater quantities in acidic soil. Which is why we always associate blue hydrangeas with acidic soil and pink hydrangeas with alkaline soil.
There are certain types of hydrangeas that will not change colour but, for the most part, you can manipulate the pH of the soil to encourage the plant to produce specific colours. You will need to measure the pH level of the soil in order to determine what colour flowers the plant will produce (if you have not already seen it in bloom). To raise the pH of the soil, you will need to add powdered garden lime or wood ash. If you want to lower the pH and make the soil more acidic, you can add ammonium sulfate or shop around for a soil acidifier or aluminum sulfate. You should monitor the soil over a longer period. The pH levels will not change immediately and it will take time for any changes to come into effect.