Why are my blue hydrangeas pink this year?

For the past few years at easter time we get a blue florist hydrangea to brighten up the house as winter draws to an end. After a few weeks the flowers die off and we store the plant in the cold room in the basement until it warms up enough outside to allow us to plant the hydrangea.

These hydrangeas will bloom steadily from year to year and even when the flowers dry they add interest to the garden. One fascinating aspect  about the hydrangea plant is that the flowers can change color from year to year. They plant is very sensitive to it’s environment, especially the pH of the soil. Actually it is based on the amount of aluminum in the soil. The more aluminum, the more blue the flower will be. The less aluminum, the more pink the flower will be. Sometimes the plant can’t make up it’s mind and you get pink and bluish flowers on the same plant.

To get hydrangea to be pink increase the pH of the soil (more alkaline) so the plant will not take up aluminum from the soil. This can be done by adding dolomitic lime a few times a year or by using fertilizer with high levels of phosphorus.

To get the hydrangea to be blue then decrease the pH of the soil (more acidic) by adding aluminum sulfate to the soil or by adding organic material that tends to be more acidic such as pine needles or even coffee grounds.

So the reason our blue hydrangeas where pink this year is that our soil became “sweeter” and less acidic. I had assumed that with the hydrangeas so close to our woodland that the large evergreen trees would make the soil more acidic and that I wouldn’t have to add a lot of organic material this year. I guess this was a bad assumption because we have a lot of pink hydrangeas.