5 Interesting Facts You Didn't Know About Hydrangeas Hydrangeas are a fan-favorite shrub. And there is some rich history behind these cluster flowers we all know and love. Here are 5 things you didn't know about hydrangeas (until now). 1. Meaning Behind the Name This explains hydrangeas' need for lots of water to thrive. 2. Hydrangea Symbolism Ancient emperors would give them to their maidens as a sign of thanks. 3. Are They Poisonous or Not? 4. Cheating the Flower Color The more alkaline, the pinker your hydrangeas will be. Science for the win! 5. Hydrangea Day