Answer: In my experience, potentilla shrubs perform best when trimmed back quite hard each spring, by about half or so. If you find that the center of the plant is very crowded, you could also trim back some of the oldest thickest stems to closer to the ground and thereby thin it out a bit. They bloom on new growth of the season, so the early spring trimming stimulates blooms. It also allows you the opportunity to remove any winter damaged stems and to shape the plant. After the first heavy flush of blooms, another lighter trim just removing the tips can help bring on another fresh set of blooms later in the summer.
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