I would try a standard lawn fertilizer with a 3-1-2 ratio of nutrients. About a quarter cup sprinkled evenly around each shrub in a 4 foot circle would be fine. Then water it in well. I would not fertilize it now but wait until late winter. You can repeat the fertilizing in spring to mid summer if you feel it is needed.
Make sure the plant is getting plenty of sun as this could be another cause of lack of blooms.
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