A blue hydrangea is the jewel in the crown of any British garden; however, certain varieties can change colour if certain conditions are not met. This can spell disaster if the last thing you want creeping into your garden is a frothy pink or purple bloom.
If you want to keep your plant beautifully blue, rather than pink, you need to maintain high levels of soil acidity. To keep a hydrangea blue, you need a pH of less than 5.5. If the pH rises to between 5.5 and 6.5, the blooms will turn purple, and if it goes above a pH of 6.5, the flowers will turn pink.
