Root. In the computer world, root refers to the top-level directory of a file system. The word is derived from a tree root, since it represents the starting point of a hierarchical tree structure.
Use a fertilizer with high levels of phosphorus. Phosphorus helps to prevent aluminum from creeping into the system of the hydrangea. Choose a fertilizer close to the ratio of 25/10/10 (Phosphorus is the middle number).
Hydrangeas have cyanide in them, and just two spliffs can be lethal. I'm not sure what it is about them that gives the high, and if cyanide has anything to do with it though. Apple pips also have cyanide in them too.