Answer: Hydrangeas should do well if given a top dressing of good quality compost along with a general purpose fertilizer for acid loving plants such as Hollytone in the spring. Read and follow the directions on the fertilizer label for how much to use.
Blue hydrangeas should show a good blue color in soil that has an acidic pH. In your area, the soil should naturally be acidic enough to give a good blue. For this reason I do not think you will need to use the aluminum sulfate.
Aluminum sulfate is sometimes used as a soil acidifier. But if used to excess, it can cause toxicity problems. Also, any changes in pH should be done gradually.
If your hydrangea blooms pink, indicating an alkaline soil pH and/or a lack of aluminum in the soil, please work with your local county extension to run some basic soil tests and then based on the test results, work gradually to amend the soil to encourage blue colored flowers.
In the meantime, you can apply bone meal in fall or spring. It is slow acting, so you should still use the general purpose fertilizer.
Q&A Library Searching Tips