Hi Sunnyvalley,
There is lots of growing season left, yes indeed. I usually apply the Epsom Salts monthly during the growing season. It will help to kickstart a new flush of blooms.
You can't really over apply the Epsom Salts. It is not a fertilizer. What it does is help the plant uptake the nutrients. I'm a lazy gardener and apply the Epsom Salts around the rose and let the rain or when watering dissolve and soak it in. It takes a while (several days) for the full cup to dissolve.
