Maintaining purple hydrangeas requires special care. To prevent them from fading, you must keep their pH level between 5.2 and 5.5. Incorrect pH levels can result in blooms turning blue or pink.
First, test your soil’s pH level by taking a sample to the local garden center for testing. While bluish hydrangeas may look more desirable, when the soil is too alkaline and its pH rises over 7, plants tend to produce mostly blue flowers – no matter what color was initially planted!
Second, manipulate your soil accordingly with amendments like mulch or compost, which will increase acidity and help lower the pH levels of your soil significantly. Or use an iron chelate solution if you want more of an intense effect.
Third, water regularly but don’t overwater; too much water can cause nutrients to leach away faster, leaving acidic conditions that turn bloom blue quickly! Finally, add a fertilizer specifically formulated for acid-loving plants, such as those containing ammonium sulfate, every three months or so during the growing season to keep nutrient levels up as well as maintain proper balance in requirements for heavier bloom production.