 "Hydrangea paniculata" is reportedly sometimes smoked as an intoxicant, despite the danger of illness and/or death due to the cyanide.The flowers on a hydrangea shrub can change from blue to pink or from pink to blue from one season to the next depending on the acidity level of the soil.Adding organic materials such as coffee grounds, citrus peel or eggshells will increase acidity and turn hydrangea flowers blue, as described in an article on Gardenista.