Hydrangeas are very popular both as cut flowers and plants for the garden because of their big, beautiful blooms. The name comes from the constant moisture required to keep the flowers happy, healthy and blooming. In Japan, they are said to be a sign of apology or gratitude because an emperor gave them as apologies to his maidens. Blue Hydrangea flower is a symbol of expressing regret, asking someone for forgiveness and even a symbol of turning down a romantic proposal. These are the meanings you need to be careful about when gifting the blue Hydrangea flower to someone you care about.