Hydrangea Color Magic
Unlike other flowers that are bred to be a certain color, the shades of pink, blue or purple on some varieties of hydrangea are determined by the chemistry of the soil in which they are growing. But if you are trying to grow a certain color, it’s not just a simple matter of adding the correct fertilizer. If you want to change the color of your blossoms or keep the color you have, you will first need to check which cultivar of hydrangea you have planted. Some, such as oakleaf hydrangea and all of the white-blossomed varieties, will not change color no matter what soil they are grown in. Hydrangea blossom colors are affected by the pH of the soil and by the aluminum levels in the soil. Since these elements can change over time, you will need to keep up on maintaining them at the level you want, as often as several times a growing season. You can test your soil's pH with an easy at-home kit or with litmus strips. Keep in mind that you won’t see an immediate change in the flowers when you change the soil, and the process of adjusting your soil’s nutrient contents should be done gradually so you don’t shock your plants. It is easiest to control the soil conditions in a container than it is in the native soil. For container plants, use potting soil for blue flowers, but soilless potting mix for pink flowers, as many potting soils contain some aluminum.