Hold off on the Holly-Tone until fall. Your Hydrangea will spend this season adapting to its new environment and recovering from any transplant shock. Any fertilizer besides those specifically labeled for transplanting may push the plant to put on new top growth at a time when it needs to focus on establishing its root system. After this first season, fertilize your Hydrangea once a year in either spring or fall.
Used coffee grounds are good for plants and soil. Apply coffee grounds sparingly during the first few months; feel free to spread them on the soil around your plant whenever you wish after that. Both Holly-Tone Fertilizer and coffee grounds will lower the soil pH, producing blue blooms on your Endless Summer Hydrangea.