I have a hydrangea that used to have big, blue flowers. While the flowers are still healthy, they are now a dusty pink. Is the plant sick? What happened? Can I get the blue blooms back?
No, your plant is not sick. Your hydrangeas simply need a pH and nutrient adjustment. While the flower color of white-flowering hydrangeas is unaffected by soil pH, that certainly is not true with pink and blue-flowering varieties. In the case of the latter, the flower color is largely determined by the soil pH. In general, hydrangeas planted in more alkaline soils will be pink. The more acidic the soil, the bluer the flowers become. In between, they tend to take on a somewhat “muddy” appearance.
The clearest blues require the minor nutrient aluminum to develop fully. Since phosphorous tends to tie up available aluminum in the soil, one should avoid high phosphorous fertilizers if the bluer flower color is desired. The addition of aluminum sulfate is perhaps the single best way to promote bluer flowers. Use one pound (2 cups) per three feet of height around each shrub in the spring and water thoroughly.