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 hydrangeas are forming their buds, they need fast-acting fertilizer if the leaves in the plant's center are turning yellow. Treat the area around the hydrangea with 4 ounces of balanced fertilizer in early spring and again when the flowers appear.