Answer: All spirea japonica greatly benefit from hard pruning in early spring. Well established shrubs can and probably should be pruned to 6-8", younger ones should be left at 10-15" at least for a couple of years.
Prompt pruning/shearing of about 1/2 to 1/3 of the height right after initial bloom will result in rebloom within 45-60 days.
It's too late in the season to do much pruning now so hold off until spring. A 10-10-10 is a good general purpose garden fertilizer. Apply in the spring.
Best wishes with your landscape!
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