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).
When to Use Plant Food. In fertile, moist soil, plant food is not normally a requirement for hydrangeas. They prefer a rich, moist soil and do equally well in partial shade or full sunlight. Signs that your plant might need plant food would be poor growth or a lack of blooms.