Answer: Potentilla shrubs bloom on new growth, and pruning is intended to promote increased bloom. It also tidies up the silhouette of the plant. Most gardeners trim these back quite hard, sometimes removing as much as half to two thrids of the branches, in early spring, a byproduct of this is creating a neat profile at the time. After the main flush of blooms, some people will shear them off again -- but only a light shearing this time. This promotes rebloom and also tidies the plant a little bit. As far as height, the plants seem to attain their mature height each summer despite the early hard pruning. I hope this answers your question.
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