Answer: For hydrangeas with coloration that can be influenced by soil pH, adding acid would usually make the flowers blue. A pH closer to neutral or an alkaline pH would tend to make them pink. If your flowers look green after adding an acid ferilizer, that is probably the plant's response to the pH being reduced by the acid. If you stop applying acid and allow the pH to naturally drift back closer to neutral, then the flowers should turn pink again in the next year or two when the acid has leached away.
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